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ICSS EMAC LLD developers guide

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ICSS_EMAC_LLD Developers guide

Last updated: 09/09/2018

Terms and Glossary

Abbreviation Meaning Abbreviation Meaning
ICSS Industrial Communicatin Sub-System SDK Industrial Software Development Kit
PRU Programmable Real Time Unit INTC Interrupt Controller
LLD Low Level Driver SoC System On Chip. Platforms like AM335x/AM437x etc
EMAC Ethernet MAC RTOS Real Time Operating System
TRM Technical Reference Manual for an SoC. Such as this. DLR Device Level Ring - a redundancy protocol for EtherNet/IP.
Rx/Tx Packet Receive/Packet Transmit Host/CPU/Cortex Used interchangeably and refers to the Application Processor

  • Bold typeface refers to name of function/API/variable/structure.
  • Code snippets are shown as below
Sample code snippet

Document Revision Table

Document Revision
Date Revision Comments
02-Oct-2015 v.1.0 Initial Release
04-Oct-2015 v.1.1 Fixed links and images
04-July-2016 v.1.2 Added Time Triggered Send details


The Industrial SDK release from Texas Instruments enables the use of the PRU-ICSS for ethernet packet processing. This is used to implement several Industrial Ethernet based protocols including Profinet, EtherNet/IP, EtherCAT etc., The SDK contains one example for each protocol. These are available under SDK/public/examples. For more information on protocols, examples, folder structure and information on how to use the SDK, please refer to the Getting Started Guide.

In addition to these, the SDK comes with an Ethernet MAC example. This example uses two PRU's to implement two independent MAC's with two different MAC addresses and two different IP addresses. To provide an analogy, this is somewhat similar to a two port Ethernet PCIe NIC card on a PC, only here, the Ethernet interface is available along with the Host processor on a single SoC.

Since all the Industrial protocols and Ethernet MAC share the same basic software architecture a discussion of Ethernet MAC goes a long way in understanding the implementation of other protocols. This is a recommended reading for anyone trying to develop or use other Ethernet based protocols provided in the SDK.


The guide is geared towards helping developers with starting to build applications using the Ethernet MAC and as such does not contain extensive architectural and design information. Readers are expected to be well versed with PRU-ICSS hardware architecture and peripherals. A description of the PRU-ICSS can be found here.

This guide also assumes general familiarity with the SDK structure and Industrial EVM's. If you are not familiar with this then please go through the Getting Started Guide mentioned previously.

Current SDK release covers both AM335x and AM437x platforms, please refer to the TRM's for details on the SoC. The TRM's can be found here. AM335x/AM437x.

Scope of the Document

This document:

  • Enables a developer to build simple applications using the Ethernet Driver and the sample Ethernet MAC application
  • Explains the components, software organization and architecture of the Ethernet driver briefly. This is only to enable developers to use and debug the modules. A detailed discussion of the architecture is beyond the scope of this document.
  • Explains usage and simple tasks through use cases and examples
  • Helps port another TCP/IP Stack or RTOS for the Ethernet MAC example

The document follows a hands on approach and different aspects are explained through examples and code snippets, these in turn are derived from questions on the forum and field.

To prevent the guide from becoming too big and to limit it's scope a separate debugging guide has been written which covers various other aspects such as Q&A's and Debug examples with screenshots. The two documents must be used in conjunction to utilize them fully.


The code snippets in this guide are only informative, they may or may not compile if taken as it is. Developers are requested to consult the API guide and other relevant user guides for exact coding details.

Software Architecture

The ICSS EMAC consists of driver + firmware implementation. Firmware refers to the code running on the two PRU's which are part of ICSS while driver refers to that portion of code running on host which is directly associated with the firmware. The two PRU's are responsible for reception of packets while Host runs higher level tasks.

Logically the software on host can be partitioned into

  • Ethernet Driver - Copying packet data and providing to upper layers. Managing PRU/ICSS.
  • TCP/IP and other network stack. NDK in this case.
  • RTOS code. SYS/BIOS in this case.
  • Peripheral initialization and management.

Out of these the first three are relevant to this discussion. Only the driver is discussed in depth while NDK and SYS/BIOS are mentioned in passing whenever relevant.

File Organization

SDK Folder structure is covered in the SDK User Guide here. This guide only covers the contents of the folder referred to as os_drivers in the user guide.

The contents of the folder os_drivers are discussed briefly:

  • lld - Refers to Link Layer Driver. This contains the core of the driver which implements the following:
    • Rx - Copying the packet received from the firmware and providing it to the TCP/IP stack
    • Tx - Providing packet from TCP/IP stack to the firmware
    • Learning/Forwarding Data Base - refer here
    • Storm Prevention implementation - refer here
    • Host Statistics implementation - refer here
  • pruss - Refers to the software which manages the PRU. It performs the following tasks
    • Initializing the PRU memory
    • Populating memory offsets, MAC addresses in PRU memory
    • Managing PRU Interrupt Controller
  • ICSS - Contains software related to the NDK (TCP/IP) Interface.
    • TCP/IP stack related initialization
    • Configuring IP address
    • ARM interrupt management

EMAC and Switch

It is important to differentiate between the two different types of implementations in SDK context because this keeps coming up while discussing SDK and it's components. An EMAC example implements two independent Ethernet MAC's using PRU 0/1, they have two different MAC, IP addresses and two different instances of the TCP/IP stack while a Switch presents a single IP and MAC address for any external entity. Another important difference which is obvious from the name is that an EMAC does not forward a packet from one port to another like a Switch.

SDK only provides a separate EMAC example, right now there is no example in the SDK for a standalone Switch on the lines of EMAC. The example that comes close to it is the EtherNetIP adapter which is a standalone Ethernet Switch running a EtherNet/IP protocol stack. Instructions on how to remove the EtherNet/IP part of it are given here.

There are some important differences between an EMAC and Switch

Differences between EMAC and Switch
EMAC Ethernet Switch

(Profinet and EtherNet/IP)

Two interface MAC addresses Single interface MAC address
PRU0 transmits on Port0 and PRU1 on Port1 PRU0 transmits on Port1 and PRU1 on Port0
Two TCP/IP instances and two IP addresses One TCP/IP instance and one IP address
Two Rx interrupts, semaphores and tasks for two ports Single Rx interrupt, semaphore and task
Two ICSS EMAC Handles Single ICSS EMAC Handle
No collision handling (independent MAC's) Collision buffer with Collision Handling

Collision refers to Queue Contention

No forwarding of packets Packets forwarded depending on forwarding rules

Ports in Driver context

Before beginning it’s important to explain the conventions used in this document, although there are two physical ports for every ICSS for the sake of convenience the Host is considered as a third port. In fact for some protocols this is the logical partitioning used. The convention used here is two physical ports and one host port.

The ports are referred to as

  • Host Port - ICSS_EMAC_PORT_0
  • Physical Port 0 - ICSS_EMAC_PORT_1
  • Physical Port 1 - ICSS_EMAC_PORT_2

This convention is followed throughout the document as well as inside the driver and firmware.

Driver Architecture and Memory Map

A detailed discussion of the architecture is beyond the scope of this document. A brief summary is provided below to explain where the data is copied to, how and why.

While discussing the ICSS Switch we are mainly concerned with 4 types of memories.


This is the memory from where ARM core operates. It's not on the SoC and hence has a lower performance. This is cached.

This contains

  • TCP/IP Buffers.
  • Learning/FDB tables.
  • Host Statistics.
  • Control structures and variables.


This is where the actual packet buffers or queues are located. There are 15 queues (Switch) or 12 queues (EMAC) in total. 4 queues for each port (including host) and 1 additional queue for each port to handle collision. This is covered later in QoS section. Developer needs to know that firmware copies the packet data here after receiving them and this is where the driver writes the packet data meant for transmission using the firmware. So this acts as a place holder for packet data before it received or transmitted. This memory resides inside the SoC (but outside ICSS) and is faster than DDR. It's buffered but non-cached. Size varies from SoC to SoC, please refer to the TRM for more details. The L3 OCMC RAM contains:

  • Host receive queues
  • Port transmit queues
  • Collision queues (not in EMAC mode)

This memory map is applicable only for EMAC application. Other applications might have their own map.

Shared Data RAM

This is specific to the PRU subsystem although access is possible from Host albeit slowly. Data common to both PRU's such as Host queue descriptors are stored here. A lot of the memory is available for protocol or application specific usage, for more details refer to the memory map. Size varies from SoC to SoC, please refer to the TRM for more details. The Shared Data RAM contains

  • Host queue descriptors
  • Buffer descriptors for all 12 queues
  • Host Rx Context for 4 Host receive queues

This memory map is applicable only for EMAC application. Other applications might have their own map.


This is similar to Shared Data RAM though meant for use only by PRU0. Access from PRU1 is also possible, so the separation is only logical, not in hardware. Size varies from SoC to SoC, please refer to the TRM for more details. The PRU0 Data RAM contains:

  • Port 0 Time Triggered Send variables
  • Port 0 Queue descriptors for 4 Tx queues
  • Port 0 Tx Context for 4 Port Tx queues
  • Port 0 Statistics
  • Port 0 MAC ID
  • Port 0 Port, Speed and Duplex information

This memory map is applicable only for EMAC application. Other applications might have their own map.


Similar to PRU0 Data RAM but for PRU1.

Quality of Service and Queues

Quality of Service is very important for an Ethernet Switch/EMAC as it allows high priority packets to be processed separately from regular packets. This provides reliability for real time traffic. In EMAC this is done using queues which are mapped to 8 VLAN based priority levels. Each queue is a block of memory on L3 used to store the packet data. Queue sizes may vary and are build time configurable from icss_emacSwitch.h, for example host queue sizes used for default EMAC application are given below, the sizes are denoted by blocks. Each block is 32 bytes in size. The sizes are limited by L3 size which are dictated by SoC. For in depth information on how to re-build the icss-emac LLD PDK component in case your use case requires re-sizing the Queue sizes, refer to [1].

#define HOST_QUEUE_1_SIZE		194	
#define HOST_QUEUE_2_SIZE		194	
#define HOST_QUEUE_3_SIZE		194	
#define HOST_QUEUE_4_SIZE		194

The transmit queues sizes are denoted separately

#define QUEUE_1_SIZE		97 	
#define QUEUE_2_SIZE		97	
#define QUEUE_3_SIZE		97	
#define QUEUE_4_SIZE		97	

So in total there are 15 queues (12 queues in EMAC), 4 receive queues for Host and 4 transmit queues for each of the two physical ports. In addition to these there is 1 collision queue each for Host and 2 ports which can hold one packet irrespective of packet size.


There are no collision queues in EMAC.

The figure below is illustrative to remember this

Switch Rx/Tx Queues

How QoS Works

Switch QoS

When a packet is received in firmware, the 3 bit PCP field of the VLAN tag is read and the packet is copied to the appropriate queue based on fixed mapping which maps 2 levels(out of 8) of QoS to one queue. So 7 & 6 map to Queue 4, 5 & 4 to Queue 3 and so on. On the driver this queue number then translates to the priority value and is used to decide how to process the packet. If a packet is missing VLAN tag then the lowest priority queue Queue 4 is chosen.


PCP to queue mapping is different for EMAC. In EMAC, the 4 Host receive queues are split into two groups. Queue 1 and Queue 2 are used for storing packets received at PRU0/Port1 and Queue 3 and Queue 4 are used for storing packets received at PRU1/Port2. So, the low priority queues are Queue 2 and Queue 4 for Port 1 and Port 2 respectively. Queue 1 and Queue 3 are high priority queues for Port 1 and Port 2 respectively.

  • All the non-VLAN tagged frames are stored in the lowest priority queue (Queue 2 for Port 1 and Queue 4 for Port 2).
  • VLAN tagged frames with “Priority Code Point (PCP)” value of 4, 5, 6 and 7 are stored in highest priority queue (Queue 1 for Port 1 and Queue 3 for Port 2).
  • VLAN tagged frames with “Priority Code Point (PCP)” value of 0, 1, 2, and 3 are stored in low priority queue (Queue 2 for Port 1 and Queue 4 for Port 2).

More on this in the next section where driver side Rx processing is discussed in detail.


  • When a queue overflows, packets are not automatically copied to the next free queue. So overflow can occur.
  • Contention/Collision queue can only handle a single packet irrespective of size, anything above is dropped.
  • On Tx side, there is no special handling with regards to QoS. Data is copied to one of the four queues based on the queuePriority field ICSS_EmacTxArgument structure passed to the ICSS_EmacTxPacket API.
  • At the moment driver/firmware doesn't support DSCP.

Data Path

Data path refers to the control flow which is executed on the driver and firmware to send or receive a packet. A basic understanding of it goes a long way in explaining the software architecture and if a developer is only trying to use the Rx and Tx capabilities of EMAC or Switch a knowledge of this is sufficient to build an application.

Rx Data Path

Rx Data Path

Packets are received in the ICSS from where they are copied by the PRU's to L3 memory. The PRU's then assert an interrupt to tell the Host about the presence of a packet. PRU avoids corruption and does not write over the memory till the packet is copied by the Host.

The flowchart shown above shows the sequence in very broad strokes. A detailed description is given below.

  1. PRU Posts an Rx interrupt to the ARM interrupt controller. For EMAC each PRU has a separate Rx interrupt, the configuration for which is done in the application (details in Interrupts).
  2. The interrupt triggers the ISR ICSS_EmacRxInterruptHandler which in turn posts a semaphore rxSemaphoreHandle to signal RxTask to empty the Rx queues.
  3. The RxTask function goes through all the queues, extracts the port/queue number and provides it to an API which copies data from L3 to DDR. The code excerpt is shown below with explanations.
/*Read till all queues are empty*/
while(allQueuesEempty != 1 && numPacketsInLoop <= ((((ICSSEMAC_Object*)icssEmacHandle->object)->emacInitcfg)->pacingThreshold))
     /*This API reads the queues and gets the queue and port number for each packet*/
     pLength = ICSS_EmacRxPktInfo(icssEmacHandle, &port_number, &queue_number);
     if(pLength > 0)
          if(queue_number >= ((ICSSEMAC_Object*)(icssEmacHandle->object))->emacInitcfg->ethPrioQueue)
               /*Based on queue priority settings decide if the packet is to be sent to the TCP/IP stack*/
               /*This API is hooked to NDK*/
               /*Protocol specific callback*/
               if(((((ICSSEMAC_Object*)icssEmacHandle->object)->callBackHandle)->rxRTCallBack)->callBack != NULL)
                    /* just dump the packet here so we do no stall the queues*/
                    ICSS_EmacRxPktGet(icssEmacHandle,(uint32_t)dest_address, queue_number, &port_number, &more);   

In the code snippet above, function ICSS_EmacRxPktInfo goes through each queue one at a time, extracts the port & queue number information for every packet and provides it to functions below. Based on the priority of the packet which is decided by the queue number (refer to discussion on QoS and queues) driver decides to either forward it to NDK, done by icssEmacHwIntRx or give it to the callback function.

The threshold for this decision is decided by the user settable parameter shown in the code above.


Anything lower than this configured value goes to the callback function. If a callback is not registered then the queue is just emptied to prevent queues from overflowing. This is done by the function ICSS_EmacRxPktGet which takes a single packet and copies it into dest_address provided as a parameter. This is not a dummy API but a basic Rx API which performs the task of copying data from L3 to DDR, even the NDK API icssEmacHwIntRx internally calls ICSS_EmacRxPktGet to fetch the packet data.

If a developer is building a custom API to process packets then he/she needs to call the API ICSS_EmacRxPktGet in their respective function, this is explained with an example below.

Doing customized packet processing:

This example is taken from EtherNet/IP adapter application where some DLR packets are processed different from other packets using a callback. For this example the value of ethPrioQueue is set to 4 or ICSS_EMAC_QUEUEPRIO4 and in this case these DLR frames have a the highest priority so they go to the callback function, developers need to set an appropriate value for ethPrioQueue based on their requirements. The callback is configured in main like this (taken from icss_eip_driver.c)

/*Packet processing callback*/
((((ICSSEMAC_Object*)icssEmacHandle->object)->callBackHandle)->rxRTCallBack)->callBack = (ICSS_EmacCallBack)processProtocolFrames;
((((ICSSEMAC_Object*)icssEmacHandle->object)->callBackHandle)->rxRTCallBack)->userArg = icssEmacHandle;

Where icssEmacHandle is the main driver handle and processProtocolFrames is the callback function whose outline is given below

void processProtocolFrames(uint32_t* queue_number, void* userArg) {
uint8_t *dstMacId = tempFrame;
ICSSEMAC_Handle eipIcssEmacHandle = (ICSSEMAC_Handle)userArg;
/*Fetch the packet*/
size = ICSS_EmacRxPktGet(eipIcssEmacHandle,(uint32_t)tempFrame, *queue_number, &port, &more); 
/*Compare Destination MAC ID and determine if this is a DLR packet*/
if(COMPARE_MAC(dstMacId, dlrMAC)) {
  processDLRFrame(eipIcssEmacHandle, tempFrame, port-1, size);

As can be seen processProtocolFrames function calls ICSS_EmacRxPktGet internally and passes the data to processDLRFrame for further processing.

Tx Data Path

Tx Data Pah

The Transmit path on host is simpler than the Rx path. As far as the developer is concerned the main API call is ICSS_EmacTxPacket. This API implements the Learning/FDB functionality. ICSS_EmacTxPacket in turn calls another API ICSS_EmacTxPacketEnqueue which performs the actual task of copying data from DDR to L3 and signals the PRU to transmit the data. ICSS_EmacTxPacket when called with the parameter ICSS_EMAC_PORT_0 in portNumber field enables learning/FDB and calls the ICSS_EmacTxPacketEnqueue with the correct port number and when called with parameter ICSS_EMAC_PORT_1 or ICSS_EMAC_PORT_1 the API directly calls the underlying API. To avoid confusion developers must always call the API ICSS_EmacTxPacket (NOT ICSS_EmacTxPacketEnqueue) with portNumber as

  • ICSS_EMAC_PORT_0 : If they do not know the port number on which to transmit.
  • ICSS_EMAC_PORT_1 or ICSS_EMAC_PORT_2 : If they know the port number

Firmware automatically appends CRC to the packet on Transmit path.


For simple and/or non time critical applications, it makes more sense to use the NDK socket API's to perform Receive and Transmit operations. An example using NDK sockets which performs both Rx and Tx is given below. For in depth information on how to use sockets please consult NDK User's guide and NDK API Reference guide.

/*Transmit to System with IP Address*/
#define DST_IP ""
#define DST_PORT 7
/*Open file session*/
fdOpenSession( (HANDLE)Task_self() );		
struct sockaddr_in sin1;
struct timeval timeout; 
/*Create UDP socket*/
/*Prepare address for connect*/
IPAddr = inet_addr(DST_IP);
bzero( &sin1, sizeof(struct sockaddr_in) );
sin1.sin_family = AF_INET;
sin1.sin_addr.s_addr = IPAddr;
sin1.sin_port = htons(DST_PORT); 
 /*Configure our Tx and Rx timeout*/
timeout.tv_sec = 0;
timeout.tv_usec = 1;
setsockopt( s, SOL_SOCKET, SO_SNDTIMEO, &timeout, sizeof( timeout ) );
setsockopt( s, SOL_SOCKET, SO_RCVTIMEO, &timeout, sizeof( timeout ) );
/*Transmit packet*/
sendto( s, pBuf, testsize, 0, (PSA)&sin1, sizeof(sin1) );
/*Receive packet*/
recv(s, pBuf, MAX_UDP_SIZE, 0);

For time critical applications with low latency requirements directly calling the API's is recommended. For Transmit this can be done by populating the packet directly(or through a stack) in a memory buffer and calling ICSS_EmacTxPacket with the buffer in a task in main(). Shown below is an example of a periodic transmit being done in main function.

/**A dummy packet*/
uint8_t dummyPkt[ETHERNET_FRAME_SIZE_60] = {0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0x00,0x00,0x00,0x00,0x00,0x00,0x08,0x00,
Void taskSendPacket(UArg a0, UArg a1) {
  /*wait for system to initialize*/
  /*Send packet in a loop every 500ms*/
  while(1) {
    /*Send packet on PORT 1*. Size is known previously/     
    ICSS_EmacTxPacket(emachandle,dummyPkt, ICSS_EMAC_PORT_1, 1, ETHERNET_FRAME_SIZE_60);

For receive the application/stack can receive the packet data directly in (uint32_t)dest_address from ICSS_EmacRxPktGet inside RxTask. Modify the ethPrioQueue value as per requirement. (Explained above)

Forwarding Rules

Forwarding Rules specify how packets are forwarded between ports and from the port to the Host. There are three basic types of forwarding scenarios. The image below shows all modes when receiving on first port. HW Port represents the physical port. These modes are not exclusive to each other and multiple modes are also allowed.

Please note that EMAC can only forward to the Host, other modes only apply to switch.

Forwarding Rules
  • Cut Through - In this mode the firmware copies the data from Rx FIFO to Tx FIFO through the registers. No data is copied to the queues, this is the fastest mode of transmit from one port to another. Advantage is low latency, disadvantage is that CRC is not checked before transmit since it lies at the end of the packet.
  • Store & Forward - In this mode the firmware copies the received data to the transmit queues on opposite port, no data is sent to the Host (Rx interrupt on Host is not asserted). CRC is checked before transmit. Many protocols like PTP use this mode.
  • Forward to Host - Data is received in the Host receive queues and an Rx interrupt is asserted to copy the data. This is the only mode available for an EMAC.

Forwarding Rules
Packet Type Forwarding Mode
Broadcast Cut through & Forward to Host
Multicast Cut through & Forward to Host

Multicast frames like PTP/DLR are handled based on protocol

Unicast (not to Host) Cut through
Unicast (to Host) Forward to Host

Interrupts and Tasks

This section deals with Interrupts and Tasks required to implement an EMAC LLD application. Since they are tied to the RTOS used, they are exported via the driver handle to the application as well as through the OSAL layer. Developers must take care to maintain correct priorities and order so as not to alter the behavior of the driver. All the interrupts and tasks enabled in an application can be checked using the SYSBIOS ROV. For more details on this tool refer to the SYSBIOS section of EMAC LLD Debug Guide.


There are six interrupts (eight if time triggered send is enabled) in an EMAC LLD coming from PRU. Other implementations like EtherNet/IP, PTP, Profinet etc may use their own interrupts. Please note that there are individual interrupts for each port because this is a dual MAC implementation, for an Ethernet switch like EtherNet/IP there are only two interrupts (no time triggered send in Switch mode).

The eight interrupts are:

  1. Rx interrupt x 2 : One for each port, both mapping to same ISR. These are used by PRU to tell ARM about the presence of a packet. For Port 0 this is interrupt number (ARM) 20 on AM335x and for Port 1 it is 21. In the mapping these are indicated by PRU_ARM_EVENT0 and PRU_ARM_EVENT1 respectively. For ethernet switch it's just PRU_ARM_EVENT0.
  2. Link interrupt x 2: One for each port, both mapping to same ISR. These are used to indicate PHY state change to Host. For Port 0 interrupt number (ARM) is 26 and for Port 1 27. In mapping these are indicated by MII_LINK0_EVENT and MII_LINK1_EVENT which map to CHANNEL7 and CHANNEL8 respectively. For ethernet switch both link events map to a single channel CHANNEL7.
  3. Tx Completion Interrupt x 2: One for each port, mapping to different ISRs. These are used by PRU to tell ARM about the completion of transmission of a packet. For Port 0 this is interrupt number (ARM) 22 on AM335x and for Port 1 it is 23. In the mapping these are indicated by PRU_ARM_EVENT2 and PRU_ARM_EVENT3 respectively.
  4. TTS Insert Cyclic Frame Interrupt x 2: One for each port, mapping to different ISRs. These are used by PRU to tell ARM that its time to insert cyclic frame. For Port 0 this is interrupt number (ARM) 22 on AM335x and for Port 1 it is 23. In the mapping these are indicated by PRU_ARM_EVENT4 and PRU_ARM_EVENT5 respectively. These are only applicable when TTS is enabled and initialized by the application.

Tx Completion Interrupts and TTS Cyclic Frame Interrupts are different PRU events, i.e., total 4 PRU events. But these map to the same interrupt and ISR per port i.e., Tx Completion Interrupt and TTS Cyclic Frame Interrupt share one ARM interrupt number and ISR for Port 1 and share one ARM interrupt number and ISR for Port 2.

There are two types of interrupts:

  • ICSS Interrupts : These are interrupts that are routed through the ICSS Interrupt controller to the Host (Refer to section 4.4.2 of AM335x TRM). It consists of interrupts asserted by the PRU as well as interrupts asserted by the peripherals (MDIO, ECAP etc) attached to the ICSS Interrupt controller.

The Host Interrupt controller has 8 usable interrupts mapped to the ICSS interrupt controller. This mapping is programmable and varies from example to example. Every example has a x_pruss_intc_mapping.h file in the sdk/examples folder where x stands for the example name. For EMAC this file is called tiemac_pruss_intc_mapping.h.

Mapping Explanation

The interrupt mapping consists of 3 parts:

  1. 8 PRU user interrupts (can be set in the firmware by writing to R31) - represented by PRU_ARM_EVENT0 to PRU_ARM_EVENT7. These are part of the 64 system interrupts (out of which 32 are usable). This includes the two link interrupts for two ports MII_LINK0_EVENT and MII_LINK1_EVENT.
  2. 10 ICSS Host channels CHANNEL0 to CHANNEL9 out of which the first two CHANNEL0 and CHANNEL1 are used internally.
  3. 8 ARM PRU interrupts represented by PRU_EVTOUT0 to PRU_EVTOUT7. These can also be seen in the ARM INTC in SoC TRM. Provided below is a screenshot from AM335x TRM showing the 8 interrupts mapped to the PRU.


The complete mapping follows the pattern

PRU user interrupts --> Host Channels --> ARM PRU Interrupts

To take an example of Rx interrupt for Port 0 (EMAC only). For switch this is the Rx interrupt for both ports.

The following line maps PRU user interrupt 0 to Host channel 2.


Host channel CHANNEL2 in turn maps to the first ARM interrupt PRU_ICSS_EVTOUT_0 through this line.


As seen from the screenshot the interrupt number for PRU_ICSS_EVTOUT_0 on AM335x is 20, so the interrupt number that must be configured for this in application should be 20 if the platform is AM335x. This is done in the following line (defined in main.c)

switchEmacCfg->rxIntNum = 20; 

This mapping alone determines which ARM interrupt number will be associated with a particular PRU user interrupt. For example the line above where PRU user interrupt 0 maps to Host channel 2 can be modified to


and the Channel to ARM interrupt map can be configured as, and the interrupt number on ARM would still remain the same i.e. 20


A question arises in this case as to the usefulness of CHANNELx. The answer is that channels allow us to map multiple PRU User interrupts and system interrupts to a single channel and in turn to a single ARM interrupt. For example take a look at the link interrupt mapping




This configuration maps both Port 0 and Port 1 interrupts to a single channel and in turn to a single ARM interrupt PRU_ICSS_EVTOUT6, which is interrupt number 26 (shown by the line below in main.c)


The link interrupt binds to a single ISR ICSS_EmacLinkISR on Host. Inside the ISR an ICSS register HW_ICSS_INTC_SECR1is checked to find out which link event MII_LINK0_EVENT or MII_LINK1_EVENT asserted the interrupt. The advantage of such an approach is that both interrupts are serviced even if they are raised at the same time.

These interrupt numbers can change from SoC to SoC so please consult TRM before making any modifications to the interrupt map. This is also one of the reasons for exporting these configurations to application so that a single driver can handle multiple SoC's others being ease of use, porting other operating systems etc.

PRU Interrupt Mapping in EMAC
PRU Interrupt Number Channel Number Host Interrupt Number ISR

Port 0 RX Interrupt

CHANNEL2 20 ICSS_EmacRxInterruptHandler

Port 1 RX Interrupt

CHANNEL3 21 ICSS_EmacRxInterruptHandler

Port 0 TX Completion Interrupt

CHANNEL4 22 ICSS_EmacTxInterruptHandlerPort1

Port 1 TX Completion Interrupt

CHANNEL5 23 ICSS_EmacTxInterruptHandlerPort2

Port 0 TTS Insert Cyclic Frame Interrupt

CHANNEL4 22 ICSS_EmacTxInterruptHandlerPort1

Port 1 TTS Insert Cyclic Frame Interrupt

CHANNEL5 23 ICSS_EmacTxInterruptHandlerPort2

Port 0 Link Interrupt


Port 1 Link Interrupt


  • Host Interrupts : Host interrupts are interrupts that are not coming via ICSS Interrupt controller. These include peripherals, EDMA, timers etc. A full list is present inside the Interrupt section of any TRM. On AM335x a total of 128 interrupts are available through this (including 8 PRU ICSS interrupts). Discussion of Host interrupts is beyond the scope of this guide as we only deal with the EMAC LLD driver here.

Some examples of Host interrupts used in the driver are DMTimer interrupts and EDMA interrupts which are available through the OSAL layer osdrv_edma.c and osdrv_osal.c

Interrupt Pacing

When packets are sent to the Host at a very high rate (this happens more often with small frames) it's possible that ARM is interrupted frequently by the PRU's, this results in packets getting dropped as the host is unable to empty the queues in time because of context switching. Interrupt pacing is a scheme used to cope with this situation. In this scheme interrupts are disabled when the first Rx interrupt is received (The PRU still keeps receiving the frames and putting them on the queues), after a certain number of packets have been processed on the Host, the interrupts are enabled once more. Since interrupts on PRU have not been disabled any pending packets will assert the interrupt again, this ensures that no packets are missed. The advantage of pacing is that a greater throughput is achieved while disadvantage is that if any critical packets need to be serviced immediately, it's possible that some delay may occur. Pacing is enabled in the driver using the variable intrPacingMode. There are two pacing modes in driver.

  • INTR_PACING_MODE1 : This is entirely ARM based, i.e. interrupts are disabled only on the Host. This does not require any firmware support. This is the scheme supported with Ethernet MAC and Ethernet IP Adapter.
  • INTR_PACING_MODE1 : In this scheme interrupts are disabled on the PRU. This requires firmware support. Only supported in Profinet right now.


Tasks are the Linux equivalent of processes in SysBIOS. A simple example to create a task from EMAC application is given below

 taskParams.priority = 15;
 taskParams.instance->name = "SwitchTask";
 Task_create(taskPruss, &taskParams, &eb);

Here taskPruss is given the job of initializing the PRU's and loading the firmware onto them. The task itself is a simple function with two arguments

 *	---task to initialize PRU---
Void taskPruss(UArg a0, UArg a1)

They can be used for simple tasks like sending or receiving a packet. To get an idea refer to the example usage for sending a packet through a call to transmit API ICSS_EmacTxPacket in a loop. If calling the task in an endless while loop developers must add a small delay inside the loop using Task_sleep(time in milliseconds) to let other tasks get some time as well, failure to do so is a common mistake that developers make.


Learning/FDB where FDB stands for Forwarding Data Base is a module that learns source MAC addresses of packets addressed to the Host and thus maintains a list of which devices reside on which port. While transmitting a packet when provided with the destination MAC address the module returns the port number on which the device resides. This avoids duplication of traffic on both ports. This module is applicable only in Switch mode, in EMAC mode this module is disabled since there is only one port.


Learning table is currently implemented as a Hash table. There is one table for each physical port. Each table has 256 buckets where a bucket has a size of 4. The bucket size and number of buckets are in turn dictated by the choice of Hashing algorithm. A detailed discussion on this topic is beyond the scope of this document, suffice to say that theoretically a hash table is capable of learning 256 * 4 = 1024 entries. The actual capacity may be lower owing to collisions.

A single bucket has

  • Four entries - For storing four MAC Id's
  • Four ageing counters - One associated with each entry
  • Number of Entries - A value which tells how many entries are there in the bucket.

A single table has

  • 256 buckets
  • Total number of entries - Sum of entries in all the buckets
  • Port State - A table has three states
    • Learning - This is the default state. All actions are permitted
    • Not Learning - No new addresses are learnt. Deletions possible.
    • Locked - No additions/deletions allowed

Collisions are handled using ageing counters, one ageing counter is associated with each of the 4 entries inside a bucket. It tells the module which entries are old and which ones are new.

API Guide & Data Structures

A learning table has the following structure

typedef struct HashTable_t{
 uint32_t totalNumEntries;	      /**Total number of entries in the hash table*/
 portState state;		      /**State of the hash table, see enum portState above*/
 HashBucket_t  entries[NUMBUCKETS];  /**Number of bucket entries*/
} HashTable_t;

The individual bucket which makes up the learning table has the following structure

typedef struct {
 MAC mac[MAX_NUM_ENTRIES];            /**Four MAC Id per bucket*/
 uint8_t timerCount[MAX_NUM_ENTRIES]; /**Timer count used for ageing and conflict resolution*/
 uint8_t numEntries;                  /**Number of MAC entries in the bucket, 4 means it is full*/
} HashBucket_t;

The default values are


The algorithm assumes these values and they cannot be changed at present.

API descriptions are only for information, developers are requested to use corresponding IOCTL calls. The IOCTL command for Learning/FDB modules is ICSS_EMAC_IOCTL_LEARNING_CTRL

Adding A MAC address : The corresponding API for this is

void updateHashTable(uint8_t* macId, uint8_t portNum, HashTable_t *tablePtr,ICSSEMAC_CallBackConfig* exceptionCallBack)

The API is integrated inside ICSS_EmacRxPktGet so developer need not call it separately, if at all it is required please use the IOCTL call for this. IOCTL Param value is ICSS_EMAC_LEARN_CTRL_UPDATE_TABLE

Looking up an Entry : The corresponding API for this is

uint8_t findMAC(const uint8_t * macId, HashTable_t *tablePtr)

Integrated with driver inside ICSS_EmacTxPacket, use IOCTL Param value ICSS_EMAC_LEARN_CTRL_FIND_MAC

Removing a MAC address : The corresponding API for this is

uint8_t removeMAC(uint8_t * macId, HashTable_t *tablePtr)

Entries are removed automatically upon ageing, if forced removal is required use IOCTL Param value ICSS_EMAC_LEARN_CTRL_REMOVE_MAC

Ageing an Entry : The driver already implements this inside the periodic task which is called every 100 NDK Ticks _HwPktPoll() but users can call it as well. IOCTL Param value ICSS_EMAC_LEARN_CTRL_INC_COUNTER

The corresponding API for this is

void incrementCounter(HashTable_t *tablePtr)

Removing an Aged Entry : The corresponding API for this is

void ageingRoutine(uint8_t portNum, HashTable_t *tablePtr)

Integrated with driver. IOCTL Param value ICSS_EMAC_LEARN_CTRL_AGEING

Changing Port State : Change the port state to appropriate value. This is useful in the implementation of requirements specified by IEEE 802.1D.

The corresponding API for this is

void changePortState(portState state, HashTable_t *tablePtr)

As part of changing port state the module implements locking of a port (where addition/deletion of entries is not possible), ageing (age the entries to simulate passage of time). Not integrated with driver, application must do it. IOCTL Param value ICSS_EMAC_LEARN_CTRL_SET_PORTSTATE

Flushing/Clearing the entire Table : The corresponding API for this is

void purgeTable(uint8_t portNum, HashTable_t *tablePtr)

Not integrated with driver, call separately using IOCTL Param value ICSS_EMAC_LEARN_CTRL_CLR_TABLE


The module is integrated with the driver so a developer need not bother about calling the API's separately in the application unless there is a specific need to

  • Add a MAC ID
  • Remove a MAC ID
  • Lock the Port or change it's state

The ageing module is called inside _HwPktPoll (which is a periodic NDK task, more info in the porting guide) via an IOCTL call, to age faster please call the routine separately in another task. Changing the time period of _HwPktPoll is not recommended as many other tasks are performed in this.

Storm Control

Strom control or Storm prevention is a feature that limits the number of broadcast and multicast packets going to the host and/or cutting through to the other port. Since broadcast and multicast packets are sent over all the ports of a switch they have the potential to create a storm which drowns all other traffic on the network, in this regard this is a very important feature for the switch.


Storm prevention is implemented on the two PRU's as a credit based scheme. When the feature is enabled, every time a multicast or broadcast packet is received a counter referred to as storm prevention credits is decremented and the packet is sent to the host as well as cut through. If the counter value is 0 then the packet is dropped. The counter is stored on respective PRU DMEM's and is reset after a fixed period by the Host. The combination of this period and credit value decides the rate of acceptance/rejection.

The mechanism is shown below in the diagram

Storm Prevention architecture Industrial.jpeg

The Storm prevention implementation is similar in both PRU's but implemented separately, so it's possible to turn it off selectively for each port. As of now the multicast and broadcast storm prevention functionalities are clubbed together but it is proposed to have them separate in the future.

API Guide & Data Structures

The main parent structure for Storm Prevention is

typedef struct {
 uint8_t suppressionEnabled;   /** enable/disable storm prevention*/
 uint16_t credits;             /** Number of packets allowed in a time interval*/
} stormPrevention_t;

There is an instance of this structure for each port

API descriptions are only for information, developers are requested to use corresponding IOCTL calls. The IOCTL command for Learning/FDB modules is ICSS_EMAC_IOCTL_STORM_PREV_CTRL

Enabling Storm Prevention  : The corresponding API for this is

void ICSS_EmacEnableStormPrevention(uint8_t portnum, ICSSEMAC_Handle icssEmacHandle)


Disabling Storm Prevention : Similar to enablement, variable set to False. The corresponding API for this is

void ICSS_EmacDisableStormPrevention(uint8_t portnum, ICSSEMAC_Handle icssEmacHandle)


Resetting the counters : This is called inside _HwPktPoll which is the NDK tick function. The time period of this tick function (default 100ms) in combination with credits value decides the rate at which Storm Prevention works. This is called by default inside the driver.

The corresponding API for this is

void ICSS_EmacResetStormPreventionCounter(ICSSEMAC_Handle icssEmacHandle)


Changing the rate : To change how many packets are accepted or rejected change the value in the structure. At every iteration these values are written to the data RAM by the ICSS_EmacResetStormPreventionCounter API. The scheme through which this occurs is explained in the design description above

The corresponding API for this is

void setCreditValue(uint16_t creditValue, stormPrevention_t* stormPrevPtr)



Most often Storm Prevention is the main reason for users not being able to receive a packet, esp if the rate is configured incorrectly. So first verify if it is enabled for that port. This can be done by

  • Checking structure variable : See the value of suppressionEnabled variable in the structure.
  • Checking memory : See the memory offset STORM_PREVENTION_OFFSET in the corresponding data RAM. The first bit of the byte location tells you whether the logic is enabled on the port.
  • Disabling Storm Prevention : This is the easiest and preferable for someone not using an emulator. Use the corresponding IOCTL call.

To quickly verify if the logic is indeed dropping packets, try sending some broadcast packets at line rate to the device and check the value of PRU statistics variable stormPrevCounter. See statistics section on how to read this variable.


Statistics on ICSS Switch provide a great deal of information on what's going on with the switch. They are enabled by default and provide provide port specific statistics. They are also a great debugging tool and should be the first thing a developer should look at if they suspect any issue with Rx or Tx.


The Statistics are divided into

  • Statistics on PRU : Since the LLD functionality is implemented on the PRU's the majority of statistics are implemented on them. The count for each port is stored on the respective Data RAM's starting at the offset STATISTICS_OFFSET. The map is shown below
  • Statistics on Host : The packets coming to the Host are counted once again, this is useful for debugging purposes and to measure throughput (from the PRU to Host) if required. Some statistics like "Unknown protocol type" are only implemented on the Host.

Functionally the statistics are classified into

  • Rx/Tx related statistics : This includes count of broadcast, multicast and unicast packets and their derivatives. Only valid packets are part of this which means that an Rx packet which has been dropped because of storm prevention will not be counted.
  • Error Counters : This includes statistics such as Dropped frames, Rx/Tx errors etc.
  • Other statistics : Includes statistics related to 802.1 CSMA/CD, number of link breaks etc.

A description of PRU statistics along with corresponding memory map is given below.

PRU Statistics Description & Memory Map
Name of Variable Description Name of Offset

Refer to icss_emacSwitch.h

Offset in PRU DRAM 0/1
txBcast Number of broadcast packets sent TX_BC_FRAMES_OFFSET 0x1F00
txMcast Number of multicast packets sent TX_MC_FRAMES_OFFSET 0x1F04
txUcast Number of unicast packets sent TX_UC_FRAMES_OFFSET 0x1F08
txOctets Total number of octets sent, includes all packets TX_BYTE_CNT_OFFSET 0x1F0C
rxBcast Number of broadcast packets received RX_BC_FRAMES_OFFSET 0x1F10
rxMcast Number of multicast packets received RX_MC_FRAMES_OFFSET 0x1F14
rxUcast Number of unicast packets received RX_UC_FRAMES_OFFSET 0x1F18
rxOctets Total number of octets received, includes all packets RX_BYTE_CNT_OFFSET 0x1F1C
lateColl Number of packets that suffered collisions late into Tx LATE_COLLISION_OFFSET 0x1F20
singleColl Number of packets that suffered collision only once SINGLE_COLLISION_OFFSET 0x1F24
multiColl Number of packets that suffered collisions more than once MULTIPLE_COLLISION_OFFSET 0x1F28
excessColl Number of packets that suffered collisions more than 15 times EXCESS_COLLISION_OFFSET 0x1F2C
txOverFlow Number of times Tx queue overflowed

(This is not supported right now)

rxMisAlignmentFrames Number of frames with uneven number of bytes in an octet

(This is not tested)

stormPrevCounter Number of packets dropped due to storm prevention STORM_PREVENTION_COUNTER 0x1F38
macRxError Number of packets with Rx MAC Error RX_ERROR_OFFSET 0x1F3C
SFDError Number of packets with incorrect SFD SFD_ERROR_OFFSET 0x1F40
defTx Number of packets deferred at least once due to CS high signal TX_DEFERRED_OFFSET 0x1F44
macTxError Number of packets facing Tx MAC Error TX_ERROR_OFFSET 0x1F48
rxOverSizedFrames Number of packets >1518 bytes RX_OVERSIZED_FRAME_OFFSET 0x1F4C
rxUnderSizedFrames Number of packets < 60 bytes RX_UNDERSIZED_FRAME_OFFSET 0x1F50
rxCRCFrames Frames with CRC/FCS Error RX_CRC_COUNT_OFFSET 0x1F54
droppedPackets Number of Received packets that were not transmitted because of link loss RX_DROPPED_FRAMES_OFFSET 0x1F5C
tx64byte Transmitted frames with size <= 64 bytes TX_64_BYTE_FRAME_OFFSET 0x1F60
tx65_127byte Transmitted frames with size >= 65 bytes and <= 127 bytes TX_65_127_BYTE_FRAME_OFFSET 0x1F64
tx128_255byte Transmitted frames with size >= 128 bytes and <= 255 bytes TX_128_255_BYTE_FRAME_OFFSET 0x1F6C
tx256_511byte Transmitted frames with size >= 256 bytes and <= 511 bytes TX_256_511_BYTE_FRAME_OFFSET 0x1F70
tx512_1023byte Transmitted frames with size >= 512 bytes and <= 1023 bytes TX_512_1023_BYTE_FRAME_OFFSET 0x1F74
rx64byte Received frames with size <= 64 bytes RX_64_BYTE_FRAME_OFFSET 0x1F78
rx65_127byte Received frames with size >= 65 bytes and <= 127 bytes RX_65_127_BYTE_FRAME_OFFSET 0x1F7C
rx128_255byte Received frames with size >= 128 bytes and <= 255 bytes RX_128_255_BYTE_FRAME_OFFSET 0x1F80
rx256_511byte Received frames with size >= 256 bytes and <= 511 bytes RX_256_511_BYTE_FRAME_OFFSET 0x1F84
rx512_1023byte Received frames with size >= 512 bytes and <= 1023 bytes RX_512_1023_BYTE_FRAME_OFFSET 0x1F88

API Guide & Data Structures

As discussed above there are two data structures for Statistics.

  1. PRU based
  2. On Host

Shown below are the members of Host Statistics. The members of PRU statistics are listed in the memory map.

typedef struct {
 volatile uint32_t txUcast;			/**Number of unicast packets sent*/
 volatile uint32_t txBcast;			/**Number of broadcast packets sent*/
 volatile uint32_t txMcast;			/**Number of multicast packets sent*/
 volatile uint32_t txOctets;			/**Number of bytes sent*/
 volatile uint32_t rxUcast;			/**Number of unicast packets rcvd*/
 volatile uint32_t rxBcast;			/**Number of broadcast packets rcvd*/
 volatile uint32_t rxMcast;			/**Number of multicast packets rcvd*/
 volatile uint32_t rxOctets;			/**Number of Rx packets*/
 volatile uint32_t rxUnknownProtocol;	        /**Number of packets with unknown protocol*/
 volatile uint32_t linkBreak;			/**Number of link breaks*/

As one can see most of the members are identical to that of PRU statistics (they are a subset) and if all packets are sent to the Host then these member values for PRU and Host statistics should match.

API descriptions are only for information, developers are requested to use corresponding IOCTL calls. The IOCTL command for Statistics module is ICSS_EMAC_IOCTL_STATS_CTRL

Reading PRU Statistics  : To fetch PRU statistics an M2M copy is done from the PRU Data RAM to the PRU statistics structure on DDR. To get the values correctly the memory layout on both sides should be identical. Developers should not modify the member order in pruStatistics_t. Doing so can give incorrect results

Host statistics are updated on the fly in the structure as packets are received (ICSS_EmacUpdateRxStats ) or transmitted (ICSS_EmacUpdateTxStats ) so there is no separate API to collate them.

The corresponding API for this is

void ICSS_EmacReadStats(uint8_t portNum, ICSSEMAC_Handle icssEmacHandle)


Clearing PRU and Host Statistics  : To clear the values do memory write to the structure memory, PRU data RAM and initialize to 0.

The corresponding API for this is

void PurgeStats(uint8_t portNum, ICSSEMAC_Handle icssEmacHandle)



Statistics are a great tool to debug issues on the switch. To get them in the application use the IOCTL calls to get and clear statistics

While IOCTL calls provide access to statistics in the application. If someone is using CCS then another quick way to see if there is any activity on the Ports is to directly go to the PRU data RAM offset STATISTICS_OFFSET and see the values directly in memory Refer Debug guide on how to see data RAM values directly in CCS.

Memory Map

The memory map here refers to the Shared Data RAM memory map in ICSS. L3 map is not of much use to the developer while DDR map is dynamic and is part of the application. The goal of providing this is to help the developer in debugging. Based on the memory map one can directly look at the memory in a CCS + Emulator environment and verify if driver/firmware is working correctly.

The memory map can be found in icss_emacSwitch.h under os_drivers/lld/emac and is common to firmware and driver builds

ICSS Shared Memory Map
Shared Memory Offset Value PRU0 Data RAM Value PRU1 Data RAM Value
0x0000 - 0x1C10 Buffer Descriptor Offsets

For Host Queues

0x0000 - 0x0400 Reserved for Future Use 0x0000 - 0x0400 Reserved for Future Use
0x1C10-0x2010 Multicast Filtering Table

(Disabled for EMAC)

0x0400-0x1EC0 Available for Protocol/Application 0x0400-0x1EC0 Available for Protocol/Application
0x2010-0x2400 Reserved for Future Use 0x1EC0-0x1F00 Port Queue Offsets 0x1EC0-0x1F00 Port Queue Offsets
0x2400-0x3000 Available for Protocol/Application 0x1F00-0x1F8C Port0 Statistics

(Map provided above)

0x1F00-0x1F8C Port1 Statistics

(Map provided above)

0x1F8C Port0 Storm Prevention

Control Variable

0x1F8C Port1 Storm Prevention

Control Variable

0x1F90 Port0 Link Speed

0x64 - 100Mbps

0xA - 10Mbps

0x1F90 Port1 Link Speed

Same as Port0

Any other value is illegal

0x1F94 Port0 Link Status

0x1 - Link Up

0x0 - Link Down

0x1F94 Port1 Link Status

Same as Port0

0x1F9A Port0 Control

0x1 - Rx Disabled

0x0 - Rx Enabled

0x1F9A Port1 Control

Same as Port0

0x1FA0 Port0 MAC ID

6 bytes

0x1FA0 Port1 MAC ID

6 bytes



The SDK uses SYS/BIOS as it's RTOS. Configuration for the RTOS is done through RTSC tool chain integrated with CCS. SYS/BIOS is provided free of cost and is a very capable RTOS for typical use cases with minimal latency.

The driver is written in a manner such that there is very little dependency on the Operating System. All dependence on SYS/BIOS is abstracted to OSAL (Operating System Abstraction Layer) and developers are integrate their own operating systems.

OSAL consists of

  1. Interrupt management
  2. Task and Semaphore management, Mailbox
  3. Management of peripherals like DMTimer, BIOS Timers

The osdrv layer deals with RTOS and other OS related tasks in general, within this layer the relevant files which deal with OSAL layer are osdrv_osal.c and osdrv_osal.h. Developers are requested to port the API's within these two files to their own Operating System. This is described in detail in the section Porting Guide


The Industrial SDK uses NDK as it's TCP/IP stack. API reference guide here. Like SYS/BIOS the module is imported externally through RTSC (refer Debug Guide) and managed through the application configuration file (am335x_app.cfg and am437x_app.cfg)

NDK recommends it's own abstraction layer which is called NIMU (Network Interface Management Unit). This layer is implemented in the driver. Relevant source files are

  • icss_ethdriver.c
  • icss_nimu_eth.c
  • icss_switch_emac.c

Understanding the NIMU layer helps in porting another TCP/IP stack to the example. The NIMU layer is explained in this guide

Porting guide covers all aspects of using a custom TCP/IP stack to the EMAC LLD example.


The ICSS EMAC Handle is a main driver handle which provides access to all members, variables, registers and addresses in the SoC.

It is the application's task to allocate memory for the handle and pass it to the driver initialization API. The handle is also required as a parameter for most of the external API's and all IOCTL calls in the driver so it's important to understand it's members.

The members of the EMAC Handle are discussed in detail here

The sample code for Handle allocation and initialization (from the example application) is shown below

/*Declare the EMAC Handle*/
ICSSEMAC_Handle emachandle; 
/*Declare the PRUSS Handle*/
PRUICSS_Handle handle; 
/*Allocate memory for EMAC and PRUSS Handle*/
handle = (PRUICSS_Handle)malloc(sizeof(PRUICSS_Config));
handle->object = (PRUICSS_V1_Object*)malloc(sizeof(PRUICSS_V1_Object));
handle->hwAttrs = (PRUICSS_HwAttrs*)malloc(sizeof(PRUICSS_HwAttrs));
emachandle = (ICSSEMAC_Handle)malloc(sizeof(ICSSEMAC_Config));
/*Initialize the EMAC*/
ICSSEmacDRVInit(emachandle, 0);
/*Initialize PRUSS*/
PRUSSDRVInit(handle); /* ICSS_M instance 0 */
/*Assign PRU handle to EMAC handle making it the parent structure*/
((ICSSEMAC_Object*)emachandle->object)->pruIcssHandle = handle;
((ICSSEMAC_Object*)emachandle->object)->emacInitcfg = switchEmacCfg;


IOCTL implementation for the switch drivers is identical to the Unix/Linux based IOCTL calls. They provide the application a convenient method to access driver/kernel space parameters or modify them.

Developers are expected to familiarize themselves with the full list of IOCTL calls so that they can utilize all the features provided. This is even more important when working in an Application/OS kind of environment where access to an emulator is not available.


The primary IOCTL call is through the API ICSS_EmacIoctl which is implemented in the file icss_emacFwInit.c An IOCTL call uses two parameters to find out which driver API to call

  1. ioctlCommand : Is used to locate the module (Statistics/ Port control etc) which should be called.
  2. ioctlParams : Is used to give module specific instructions

ioctlParams consists of

  • command : Indicates which specific API to execute
  • ioctlVal : Sometimes the API may require specific input, this is used to provide that.

For example to disable receive functionality on a port the following code is used. This code is part of Link interrupt functionality where receive is disabled when PHY detects a link down.

ioctlParams.ioctlVal = &ioctlvalue;
ICSS_EmacIoctl(icssEmacHandle, ICSS_EMAC_IOCTL_PORT_CTRL, ICSS_EMAC_PORT_1, (void*)&ioctlParams); 

Here ICSS_EMAC_IOCTL_PORT_CTRL refers to the ioctlCommand while ICSS_EMAC_IOCTL_PORT_CTRL_DISABLE is the command part of ioctlParams which tells which action to perform, in this case disabling the port. Port selected is ICSS_EMAC_PORT_1 which refers to Port 1.

A complete list of commands and actions is given below.

API Guide & Data Structures

IOCTL Command structure

 typedef struct ICSSEMAC_IoctlCmd {
   uint8_t command;
   uint8_t* ioctlVal;

There is only one API for IOCTL. It's defined below

uint8_t ICSS_EmacIoctl(ICSSEMAC_Handle icssEmacHandle, uint32_t ioctlCommand, uint8_t portNo, void *ioctlParams)

The possible values for ioctlCommand are

  • ICSS_EMAC_IOCTL_PORT_CTRL : Select Port Control Operations. Enable/Disable Rx for the specified port.
  • ICSS_EMAC_IOCTL_LEARNING_CTRL : Select Learning/FDB module.
  • ICSS_EMAC_IOCTL_STORM_PREV_CTRL : Select Storm Prevention module.
  • ICSS_EMAC_IOCTL_STATS_CTRL : Select Statistics module.
  • ICSS_EMAC_IOCTL_TTS_CTRL : Select Time Triggered Send Configuration module. Enable/Disable TTS for the specified port.
  • ICSS_EMAC_IOCTL_TTS_STATUS_CTRL : Select Time Triggered Send Query module. Get TTS status and other details for the specified port from PRU firmware.

Possible values for ioctlParams are

    • ICSS_EMAC_LEARN_CTRL_UPDATE_TABLE : Add an entry to the Hash table.
    • ICSS_EMAC_LEARN_CTRL_CLR_TABLE : Clear the Learning Table for the specified port.
    • ICSS_EMAC_LEARN_CTRL_AGEING : Age out old entries from the table.
    • ICSS_EMAC_LEARN_CTRL_FIND_MAC : Find the port number given a MAC ID.
    • ICSS_EMAC_LEARN_CTRL_REMOVE_MAC : Remove a MAC ID from the Learning Table
    • ICSS_EMAC_LEARN_CTRL_INC_COUNTER : Age the entries with time by calling this periodically
    • ICSS_EMAC_LEARN_CTRL_INIT_TABLE : Initialize the learning table
    • ICSS_EMAC_LEARN_CTRL_SET_PORTSTATE : Set the Port state to value defined by the enum type portState
  • ICSS_EMAC_IOCTL_STATS_CTRL : Refer to Statistics API's
    • ICSS_EMAC_IOCTL_STAT_CTRL_GET : Get the statistics
    • ICSS_EMAC_IOCTL_STAT_CTRL_CLEAR : Clear all stat counters
  • ICSS_EMAC_IOCTL_STORM_PREV_CTRL : Refer to Storm prevention API's
    • ICSS_EMAC_STORM_PREV_CTRL_ENABLE : Enable Storm Prevention
    • ICSS_EMAC_STORM_PREV_CTRL_DISABLE : Disable Storm Prevention
    • ICSS_EMAC_STORM_PREV_CTRL_SET_CREDITS : Set how many BC/MC packets are allowed in a period of 100 NDK Ticks (Time period of _HwPktPoll())
    • ICSS_EMAC_STORM_PREV_CTRL_INIT : Initialize Storm Prevention
    • ICSS_EMAC_STORM_PREV_CTRL_RESET : Renew the storm prevention counters, this allows more packets to come through once existing credits have expired. This must be called periodically in _HwPktPoll()
  • ICSS_EMAC_IOCTL_PORT_CTRL : For Rx Enable/Disable operations. There are no sub-commands here. Whether to enable or disable is decided by the value of ioctlVal


Using IOCTL to debug the issues is encouraged. This is easier than trying to connect an emulator and reading the values at run time. There are numerous instances of it's usage. A quick search for the API ICSS_EmacIoctl throughout the code reveals numerous examples. One of them pertaining to Storm Control module is shown below.

In this example the storm prevention counters are reset in PRU Data RAM using IOCTL. The if/else refers to Switch or EMAC mode, rest of the code is self-explanatory

 ioctlParams.command = ICSS_EMAC_STORM_PREV_CTRL_RESET;
 /*Reset the credit values used for Storm prevention*/
 if(ICSS_EMAC_MODE_SWITCH == ((ICSSEMAC_Object*)(pi->nimuDrvHandle)->object)->emacInitcfg->portMask)
   strmPreventionEnable1 = (stormPrevention_t*)(((ICSSEMAC_Object*)(pi->nimuDrvHandle)->object)->stormPrevPtr);
   strmPreventionEnable2 = (stormPrevention_t*)(((ICSSEMAC_Object*)(pi->nimuDrvHandle)->object)->stormPrevPtr +1);
   if(strmPreventionEnable1->suppressionEnabled ||	strmPreventionEnable2->suppressionEnabled)
   	ICSS_EmacIoctl(pi->nimuDrvHandle, ICSS_EMAC_IOCTL_STORM_PREV_CTRL, NULL, (void*)&ioctlParams);
   strmPreventionEnable1 = (stormPrevention_t*)(((ICSSEMAC_Object*)(pi->nimuDrvHandle)->object)->stormPrevPtr);
   	ICSS_EmacIoctl(pi->nimuDrvHandle, ICSS_EMAC_IOCTL_STORM_PREV_CTRL, NULL, (void*)&ioctlParams);

Time Triggered Send

The EMAC Time Triggered Send (TTS) is used to expand classical Ethernet to meet deterministic, time-critical or safety-relevant conditions. TTS reduces the transmission jitter from 10us range to 40ns. TTS can be dynamically enabled and disabled by the Host. We have two well defined TTS APIs which control all TTS related EMAC aspects. Developers are advised to access these APIs using the EMAC IOCTL implementation as explained in the IOCTL section previously.

TTS Design Overview

TTS is designed to facilitate transmission of packets at pre-defined cyclic instants/triggers. The TTS API Details and Data Structures are explained below but in a broad sense we can say that while initializing TTS, the application must provide the first cyclic trigger and the cycle period. The PRU firmware then sets cyclic triggers repeatedly and shall send the packets cyclically provided that they are queued before the trigger. The following timing diagram explains the use of TTS.

Time Triggered Send Overview

Each cycle shall have a configuration time (as shown in the figure above) before each trigger. This configuration time is used to setup the start trigger and end trigger of current cycle in the PRU firmware. If the application does not set a suitable (long enough) configuration time, the PRU and perhaps even the EMAC Driver TTS API may not get enough time to setup and initialize TTS. This might result in improper functionality. The configuration time shall also be provided during initialization and shall be application specific. For example, if a response packet is to be received for the cyclic packet sent at trigger T1 and based on that response packet the next cyclic packet shall be generated, then the developer can increase/decrease configuration time accordingly to ensure that the next cyclic packet is ready before trigger T2 which shall in-turn be based on when the response packet is received.

Queue 0 (high priority queue) is reserved as the real-time queue. All packets in queue 0 are cyclic packets. On the other hand, packets from other queues are acyclic packets. Cyclic packets are sent at triggered instances, whereas acyclic packets are sent based on time availability, as shown in the figure below.

TTS Time Availability Check

The time availability check for cyclic packets means to basically check whether the acyclic packet can be transmitted such that its transmission does not overlap the next cyclic trigger, considering the size of the acyclic packet. Such a situation is represented as “Undesired Behaviour” in the above figure and PRU firmware ensures that this never happens. Only one cyclic packet will be sent out in each cycle irrespective of the number of cyclic packets available in Queue 0. There is no restriction on the number of acyclic packets sent out in each cycle but it is contingent on time availability. Cyclic packets must be queued in Queue 0 before the trigger instant else two erroneous situations are possible:

  1. If the firmware finds a packet in any other low priority queue, it will send the acyclic packet. Once an acyclic packet has been transmitted in a given cycle, no cyclic packet will be transmitted in that cycle. So, if the cyclic packet is not queued on time, it will miss the cycle and will be transmitted in the next cycle.
  2. If all the queues are empty and a cyclic packet is inserted late, it will result in increased jitter.

The above two situations are demonstrated in the figure below.

TTS Error Conditions

In the above figure, the PRU firmware ensures that the first two situations never occur but the application needs to take care of the third situation, i.e., by queueing the cyclic packet on time.

The PRU firmware makes the following assumptions regarding TTS:

  1. The cycle period is long enough to be able to transmit any cyclic packet in queue 0. Failure to ensure this will cause the cyclic packet with size greater than the allowed size (as per the period), and any cyclic packets following it, to remain in the queue.
  2. The configuration time provided (using ICSS EMAC IOCTL) is sufficient for the PRU to configure the next cycle. PRU should typically need a maximum of 10us to configure the next cycle.
  3. If the host keeps queuing packets irrespective of the fact whether the packet has been transmitted by the firmware (in accordance with the preset triggered intervals), the packets might get dropped at the driver level if the queue is full. It is assumed that this is taken care of at the host level.

TTS API Details and Data Structures

TTS has the following APIs, which are accessed using EMAC IOCTL implementation as explained in the IOCTL section previously.

int8_t ICSS_EmacTTS(const ICSS_EmacTTSConfig* ttsConfig)

This API is used to enable/disable time triggered send for Queue 0 frames.

int8_t ICSS_EmacTTSGetStatus(ICSS_EmacTTSQuery* ttsQuery)

This API is used to query time triggered send details, status and TTS parameter values from PRU firmware.

The TTS parameter structure is explained below:

typedef struct ICSS_EmacTTSConfig_s {
  ICSSEMAC_Handle icssEmacHandle;
  uint8_t portNumber;
  uint64_t cycleStartTime;
  uint32_t cyclePeriod;
  uint32_t configTime;
  uint8_t statusTTS;
  uint8_t cycTxSOFStatus;
} ICSS_EmacTTSConfig;
  • icssEmacHandle: EMAC handle for concerned EMAC instance and port.
  • portNumber: Port number for which TTS needs to be enabled/disabled.
  • cycleStartTime: A future IEP counter value at which the first cyclic packet will be transmitted.
  • cyclePeriod: TTS cycle period.
  • configTime: Configuration time for PRU to setup upcoming TTS cycle.
  • statusTTS: Enable/Disable TTS. Enable = 1, Disable = 0.
  • cycTxSOFStatus: Enable/Disable storing transmit start-of-frame timestamp for cyclic packets in memory. Enable = 1, Disable = 0.

The TTS query structure is as explained below:

typedef struct ICSS_EmacTTSQuery_s {
  ICSSEMAC_Handle icssEmacHandle;
  uint8_t portNumber;
  uint8_t statusTTS;
  uint8_t missedCycle;
  uint8_t insertCycFrameNotification;
  uint8_t cycTxSOFStatus;
  uint32_t missedCycleCounter;
  uint64_t cycTxSOF;
} ICSS_EmacTTSQuery;
  • icssEmacHandle: EMAC handle for concerned EMAC instance and port.
  • portNumber: Port number for which TTS query needs to be performed.
  • statusTTS: Whether TTS is enabled/disabled for given port. Enabled = 1, Disabled = 0.
  • missedCycle: Whether any cyclic packet missed a cycle. Missed = 1, Did not miss = 0.
  • insertCycFrameNotification: Notification to state that it’s time to insert cyclic packet. If it’s time = 1, else = 0.
  • cycTxSOFStatus: Whether storing transmit start-of-frame timestamp for cyclic packets in memory is enabled/disabled. Enabled = 1, Disabled = 0.
  • missedCycleCounter: Number of cycles missed by cyclic packets.

The application shall update the elements of the ICSS_EmacTTSConfig structure and pass its pointer to EMAC IOCTL with appropriate command to enable/disable TTS. On the other hand, the application shall only update the icssEmacHandle and portNumber elements of the ICSS_EmacTTSQuery structure and pass its pointer to EMAC IOCTL with appropriate command to retrieve the details from PRU firmware. The driver TTS API (ICSS_EmacTTSGetStatus) shall then update the elements of the structure with appropriate values.

TTS can be enabled/disabled using EMAC IOCTL as follows:

For Enable:

ICSSEMAC_IoctlCmd ioctlParams;
ICSS_EmacTTSConfig ttsConfig;
uint32_t iepRegsBase;
int8_t ret;

ioctlParams.command = 0;
ioctlParams.ioctlVal = (void *)(&ttsConfig);

ttsConfig.icssEmacHandle = icssEmacHandle;
ttsConfig.portNumber = portNumber;
ttsConfig.configTime = ICSS_EMAC_TTS_CONFIG_TIME;
ttsConfig.cyclePeriod = cyclePeriod;
ttsConfig.statusTTS = ICSS_EMAC_TTS_ENABLE;

iepRegsBase = (((ICSS_EmacHwAttrs*)icssEmacHandle->hwAttrs)->emacBaseAddrCfg)->prussIepRegs;

/*	Reading IEP Counter Value.	*/
iepCounterVal = (*((uint64_t*)(iepRegsBase + CSL_ICSSIEP_COUNT_REG0)));

/*	Calculating cycle start value by adding 100us to counter value.	*/
ttsConfig.cycleStartTime = (uint64_t)(iepCounterVal + 100000);

/*	Enabling time triggered send.	*/
ret = ICSS_EmacIoctl(icssEmacHandle, ICSS_EMAC_IOCTL_TTS_CTRL, portNumber, &ioctlParams);
assert(ret == 0);

For Disable:

ICSSEMAC_IoctlCmd ioctlParams2;
ICSS_EmacTTSConfig ttsConfig;
int8_t ret;

/*	Setting tts status to disable (Port 1)	*/
ttsConfig.icssEmacHandle = icssEmacHandle;
ttsConfig.statusTTS = ICSS_EMAC_TTS_DISABLE;
ttsConfig.cyclePeriod = 0;
ttsConfig.configTime = 0;
ttsConfig.cycleStartTime = 0;
ttsConfig.portNumber = portNumber;

ioctlParams2.command = 0;
ioctlParams2.ioctlVal = (void *)(&ttsConfig);

/*	Disabling time triggered send on PORT 1 (PRU0).	*/
ret = ICSS_EmacIoctl(icssEmacHandle, ICSS_EMAC_IOCTL_TTS_CTRL, portNumber, &ioctlParams2);
assert(ret == 0);

TTS Cyclic Frame Notification

The PRU firmware has been designed to notify the Host when it’s time to insert the cyclic packet. This helps the Host to queue the cyclic packet well before trigger time and avoid any unnecessary jitter or any other erroneous situations as mentioned previously. The firmware does this in two ways:

Polling Mode

  • In this mode the firmware sets a status bit when it’s time to insert the cyclic frame and this bit cleared when the time to insert the cyclic frame is over or the firmware has found a cyclic frame in Queue 0.
  • This status bit can be queried using the EMAC IOCTL and is reflected in insertCycFrameNotification element of the ICSS_EmacTTSQuery structure.
  • If it’s time, insertCycFrameNotification = 1, else insertCycFrameNotification = 0.
  • The application must then continuously poll for this status by repeating EMAC IOCLT calls and querying TTS status.
  • Once insertCycFrameNotification = 1, the application must queue the cyclic frame in Queue 0.

Interrupt Mode

  • In this mode, in addition to setting the status bit as in polling mode, the firmware has the capability to give an interrupt to the Host when it’s time to insert a cyclic frame.
  • The interrupt feature should be first enabled as follows during EMAC Driver Initilization.
ICSS_EmacInitConfig* switchEmacCfg;
switchEmacCfg = (ICSS_EmacInitConfig*)malloc(sizeof(ICSS_EmacInitConfig));
switchEmacCfg->ICSS_EmacTTSEnableCycPktInterrupt = ICSS_EMAC_TTS_CYC_INTERRUPT_ENABLE;
  • Also, proper interrupt mapping should be done as explained earlier in this guide.
  • Interrupt callback functions should also be registered for all concerned EMAC handles using the following API:
ICSS_EmacRegisterHwIntTTSCyc(emachandle, (ICSS_EmacCallBack)ttsCycPort1Callback);
  • Interrupts should also be enabled. Please refer to example ICSS EMAC applications from Processor SDK RTOS for further details.
  • Once the PRU firmware throws an interrupt, the registered callback function is called and this is where the application shall queue the cyclic packet to Queue 0.

ICSS EMAC LLD Dependencies

ICSS EMAC LLD is dependent on the Application/Transport layer for its proper functioning. These dependencies have been consolidated and exported to the application layer (example) to make it easy for developer to integrate the LLD with their own RTOS and TCP/IP stack.

Interrupt Configuration

ICSS EMAC LLD expects the Interrupt configuration to come from Application/Transport layer. The interrupt configuration is explained in detail in the interrupts section. Please refer to it for more details.

The LLD makes use of two interrupts for copying packets from the queues to the TCP/IP stack.

Rx Interrupt

The ICSS EMAC LLD depends on the Rx interrupt for receiving packets.The application should do the interrupt creation and should use the API ICSS_EmacRxInterruptHandler as the ISR.This will enable the ICSS EMAC LLD to receive packets. The user should make sure the arm interrupt (Rx) is mapped to correct PRUSS Event. The PRUSS Event that is used for Rx will be determined by the firmware which will be used along with the ICSS EMAC LLD

Link Interrupt

Link Interrupt informs the ICSS EMAC LLD of any Link state change. This is where the LLD informs the firmware about the Link status and the Phy configuration.The LLD expects single interrupt for both Ports. In case the Interrupt mechanism is not available, the application should call ICSS_EmacLinkISR whenever there is a link change.

Learning module Increment counter implementation

This is required for Switch implementation only. The application needs to call the IOCTL periodically, this is already done by the NDK. Refer to the API section of Learning for more details.

MDIO Configurations

ICSS EMAC LLD does not do any of the MDIO configurations. It expects the application to do following MDIO operations

  • MDIO Initialization -
  • MDIO Link Interrupt enable if MDIO Link interrupt is used

NOTE: Please refer to ti/drv/icss_emac/test/src/test_mdio.c for details of how to initialize the MDIO sub-system and how to enable MDIO link interrupts. This file contains a set of MDIO test APIs which are used by the icss emac loopback unit tests.

EMAC Configuration and How To

Network related

How to configure IP address and other IPv4 parameters

IP address, network mask and other params can be set through the NDK configuration file. See here

How to configure MAC address

MAC address is variable macId in the configuration ICSSEMAC_InitConfig. It can be set as per the application requirements. The following excerpt from ethernet_mac example shows how to do this

/*Get MAC address from eFUSE*/
/*Assign MAC ID for that particular port*/
switchEmacCfg->macId = lclMac;