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AM335x PSP User's Guide

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AM335x PSP User Guide
Linux PSP

About this Manual

This document describes how to install and work with Texas Instruments Platform Support Package (PSP) for the AM335x platform. This PSP provides a fundamental software platform for development, deployment and execution on AM335x EVM. It abstracts the functionality provided by the hardware. The product forms the basis for all application development on this platform.

In this context, the document contains instructions to:

  • Install the release
  • Build the sources contained in the release

The document also provides detailed description of drivers and modules specific to this platform - as implemented in the PSP.


This release has been tested on AM335x EVM, BeagleBone board

AM335X EVM Configuration

For more information regarding EVM Combinations & Configurations, Please refer to EVM reference manual.



Before Starting the installation of the package please make sure below system requirements are met:

  • Host machine running a version of Windows OS such as Windows XP SP3, Linux such as Ubuntu.
  • AM335x BeagleBone or EVM board

The Windows machine is used for:

  • Running CCSv5.1, which will be used to build flash writers.
  • Burn the boot images (U-Boot) onto the flash using the flash writers provided.

The Linux host is used for the following:

  • Recompiling U-Boot and the Linux kernel.
  • Hosting the NFS server to boot the EVM with NFS as root filesystem.

Either of Windows or Linux host can be used for:

  • Hosting the TFTP server required for downloading kernel and file system images from U-Boot using Ethernet.
  • Running a serial console terminal application

PSP Package Contents


The values of MM, mm, pp and bb in this illustration will vary across the releases and actually depends on individual component versions.

Extract the contents of release package on Linux host with the following command:

$ tar -xvzf

This creates a directory with the following contents:

|    |
|    |----AM335x_PSP_User_Guide.pdf
|    |----AM335x_Audio_Driver_User_Guide.pdf
|    |----AM335x_EDMA_Driver_User_Guide.pdf
|    |----AM335x_PSP_U-Boot.pdf
|    |----AM335x_PSP_McSPI_Driver_Guide.pdf
|    |
|    |----AM335x_PSP_MMC_SD_Support.pdf
|    |----AM335x_USB_User_Guide.pdf
|    |----AM335x_PSP_WDT_Support.pdf
|    |----AM335x_PSP_Flashing_Tools_Guide.pdf
|    |----nand-flash-writer.out
|    |
|    +----src
|    |    |
|    +----examples
|    |    +----am335x
|    |    |    |----edma_test.ko
|    +----kernel
|    |    +----am335x
|    |    |    |----uImage
|    +----u-boot
|    |    |----am335x
|    |    |    |----u-boot.img
|    |    |    |----MLO
|    +----kernel
|    |    |
|    |    |
|    |    |
|    |    |
|    |    |----ShortLog
|    |    |
|    +----u-boot
|    |    |
|    |    |
|    |    |----ShortLog
|    |    |
|    |    |
|    |    |
|    |    |----Readme.txt
|    +----examples
|    |    |

Instructions to extract U-Boot, Linux & Example source code from tar archive


Below steps assumes that release package is extracted inside directory represented as $AM335x-PSP-DIR:

Install U-Boot

  • U-Boot source tarball is needs to be extracted on Linux build host. This will create U-Boot source base for AM335x
$ cd $AM335x-PSP-DIR/
$ tar -xvfz

Install Linux Kernel

  • Similarly kernel source tarball needs to be extracted to have kernel source directory setup for building kernel and/or modules
$ cd $AM335x-PSP-DIR/
$ tar -xvfz
  • Various example sources are included inside $AM335x-PSP-DIR/examples/


To boot-up Linux, a target filesystem is needed. A filesystem is not included in PSP package. It should be obtained from SDK release.


GNU toolchain for ARM processors from Arago is recommended. Arago Toolchain can be found in the linux-devkit directory of the SDK here

Environment Setup

After installing the toolchain, the environment in the Linux host needs to be setup.

  1. Set the environment variable PATH to contain the binaries of the Arago cross-compiler tool-chain.
    For example, in bash:
    $ export PATH=/opt/toolchain/arago/arago-2011.09/bin/:$PATH
  2. Add the location of U-Boot tools directory to the PATH environment variable (required for mkimage utility that is built as part of U-Boot build process and is needed to generate uImage when building the kernel)
    For example, in bash:
    $ export PATH=/opt/u-boot/tools:$PATH


Actual commands to be used for setting the environment variables will depend upon the shell and location of the tools.

To help get started quickly, the PSP package comes with pre-built binaries. However, after making any changes to U-Boot and/or Linux Kernel, they have to be cross-compiled and the new binaries that are generated should be used.

Flashing Tools

On AM335x EVM, the Cortex-A8 core boots up first. On boot-up, the ARM core runs the U-Boot image which need to be present in the flash memory of the EVM.

The flash-writers are a part of the PSP package. Instructions on how to use the flash-writers in CCSv4/v5 can be found in AM335x Flashing Tools Guide.


For details about AM335x U-Boot, refer AM335x U-Boot User's Guide.

Linux Kernel

For details about AM335x Linux, refer AMSDK Linux User's Guide.

Booting Linux Kernel

Kernel along with root filesystem can either be booted from on board storage device or can be fetched over the Ethernet or UART to RAM using TFTP or serial protocols like YMODEM and booted from there. Also, the root filesystem can be formatted as JFFS2 and flashed, which, then can be mounted as MTD root block device. Please refer to the U-Boot User Guide for details about flashing and supported storage devices.

Following sections describe various kernel boot options possible.


The offsets and MTD partition numbers used in examples below may vary depending upon actual partition layout used on particular storage device. Also, selecting multiple storage device support in kernel (e.g., NAND & SPI) may change the effective partition number to be used as root partition.

Boot from MMC/SD

Make sure the Boot Mode/Configuration Select Switch is set for the MMC/SD boot mode as described in SD boot switch settings section.

Power on EVM with SD card inserted and wait for U-Boot prompt of the 2nd stage (U-Boot#) to come up on the serial console.

Setup the SD card as described in Setting Up Boot Environment on SD Card  and When Kernel Image and File system are placed in SD card.

U-Boot# setenv bootargs 'console=ttyO0,115200n8 root=/dev/mmcblk0p2 mem=128M rootwait'
U-Boot# setenv bootcmd 'mmc rescan; fatload mmc 0 0x82000000 uImage; bootm 0x82000000'

Boot from NAND

Make sure the Boot Mode/Configuration Select Switch is set for the NAND boot mode as described in NAND boot switch settings section.

Power on AM335x EVM and wait for U-Boot prompt of the 2nd stage (U-Boot#) to come up on the serial console.

When kernel uImage and JFFS2 filesystem are flashed on the NAND device:

U-Boot# nand read.i 0x81000000 280000 500000
U-Boot# setenv bootargs 'mem=128M console=ttyO0,115200n8 noinitrd root=/dev/mtdblock4 rw rootfstype=jffs2 ip=dhcp'
U-Boot# bootm 0x81000000

When kernel image is flashed on the NAND device, and NFS mounted filesystem is being used:

U-Boot# nand read.i 0x81000000 280000 500000
U-Boot# setenv bootargs 'console=ttyO0,115200n8 root=/dev/nfs nfsroot=,nolock rw mem=128M'
U-Boot# bootm 0x81000000

Boot from SPI

Make sure the Boot Mode/Configuration Select Switch is set for the SPI boot mode as described in SPI boot switch settings section.

Power on AM335x EVM and wait for U-Boot prompt of the 2nd stage (U-Boot#) to come up on the serial console.

Assuming kernel image is flashed on the SPI flash @ 0x62000 and NFS based root filesystem is used:

U-Boot# sf read 0x81000000 0x62000 0x200000
U-Boot# setenv bootargs 'console=ttyO0,115200n8 root=/dev/nfs nfsroot=,nolock rw mem=128M'
U-Boot# bootm 0x81000000

Boot over Network (Ethernet)


When setting a MAC address please ensure that the LS-bit of the 1st byte is not 1 i.e. when setting the MAC address: y in xy:ab:cd:ef:gh:jk has to be an even number. For more info this refer to the wiki page

When kernel image and ramdisk image are fetched from a TFTP server:

  • Ensure that the EVM is connected to network with DHCP and TFTP server set up
  • If the TFTP server supports negotiation between client and server, Disable it
  • Copy kernel image and ramdisk to TFTP server's root directory.
  • Set 'ethaddr' U-Boot environment variable with proper ethernet address in format 'xx:xx:xx:xx:xx:xx' (replace 'xx' with proper hexadecimal values)
  • Execute following commands at U-Boot prompt. Assuming kernel image name as 'uImage' and ramdisk file name as 'ramdisk.gz'
U-Boot# setenv autoload no
U-Boot# dhcp
U-Boot# setenv serverip <Server IP Address>
U-Boot# tftp 0x81000000 uImage
U-Boot# tftp 0x82000000 ramdisk.gz
U-Boot# setenv bootargs 'mem=128M console=ttyO0,115200n8 root=/dev/ram0 initrd=0x82000000,40M ramdisk_size=32768 ip=dhcp'
U-Boot# bootm 0x81000000
  • Alternatively, kernel can be made to use the same IP address as assigned to U-Boot instead of doing DHCP request again by setting U-Boot parameters as follows:
U-Boot# print ethaddr                          <-- Check if MAC address is assigned and is unique
U-Boot# setenv ethaddr <unique-MAC-address>    <-- Set only if not present already, format xn:yy:zz:aa:bb:cc
U-Boot# setenv bootcmd 'dhcp;run addip; tftp 81000000 uImage;bootm'
U-Boot# setenv hostname <unique-hostname>
U-Boot# setenv addip 'setenv bootargs ${bootargs} ip=${ipaddr}:${nfsserver}:${gatewayip}:${netmask}:${hostname}:eth0:off'
U-Boot# setenv autoload no
U-Boot# setenv nfsserver <nfs-server-ip>         <-- Make sure the same NFS server IP is used below
U-Boot# setenv bootargs 'console=ttyO0,115200n8 root=/dev/nfs nfsroot=<nfs-server-ip>:<path-to-nfs-share>,nolock rw mem=128M'
U-Boot# setenv serverip <tftp-server-ip>
U-Boot# saveenv
U-Boot# boot
  • After saving the environment variables, they need not be setup again on reboot unless a change is required.
  • Note that the above example uses NFS mounted root file system accessed over 'eth0' interface

'ethaddr' need not be set for devices having valid MAC IDs set. In such cases, U-Boot will automatically detect and set the ethernt address (should show message like "Detected MACID:...").

Various Module User's Guide

GPIO Driver

AM335X has four GPIO modules provides 32 dedicated general-purpose pins with input and output capabilities, total 0 - 127 pins are available for usage.

GPIO Driver User Guide have more details of driver usage

DCAN Driver

DCAN Driver User Guide

EDMA3 Driver

AM335x EDMA Driver's Guide

Audio Driver

The audio driver in the PSP package conforms to the ASoC framework in the Linux kernel. The current driver supports audio capture and playback using the AIC3106 codec on the EVM. For more details on the audio driver refer to the following page: AM335x Audio Driver's Guide

USB Driver

The USB subsystem includes two USB (Mentor Graphics USB2.0 OTG) controller.

AM335X USB Driver User Guide 04.06.00.

MMC/SD driver

MMC/SD Driver supports MMC/SD/SDHC/uSD cards. HSMMC peripheral (and driver) has support for 4 data lines at the max operating frequency of 48MHz. HSMMC is a slave DMA peripheral and uses EDMA to move data between SD card and system memory.

Please refer AM335x MMC/SD Driver's Guide for more details.

McSPI Driver

Please refer AM335x_PSP_McSPI_Driver_Guide.pdf in the release package or refer online AM335x McSPI Driver's Guide.

Watchdog Timer (WDT)

The following document covers the details regarding the watchdog timer in AM335x:

Please refer AM335x PSP WDT Driver User Guide.

CPSW Driver

CPSW (Common Platform Switch) is a ethernet switch consisting of 3 MAC ports.

Please refer AM335x CPSW (Ethernet) Driver's Guide for more details.

LCD Frame Buffer Driver

LCDC (LCD controller) is updated version of LCDC found on DA850.

Please refer AM335x LCD Controller Driver's Guide for more details.

Touchscreen Driver

The touchscreen controller is an 8 channel general purpose ADC, with optional support for touchscreen conversions for a 4/5/8-wire resistive panel.

Please refer AM335x Touchscreen Driver's Guide for more details.

Power Management

Refer to AM335x Linux Power Management User Guide for more details.

NAND Driver

Please refer AM335x NAND Driver's Guide for more details.

PWM Driver

Please refer AM335x PWM Driver's Guide for more details.

ADC Driver

Please refer AM335x ADC Driver's Guide for more details.

RTC Driver

AM335x has an internal RTC. The driver for this present under <kernel-src>drivers/rtc/rtc-omap.c

The RTC driver conforms to the RTC framework in the kernel. For more details on the RTC driver please refer to rtc.txt under kernel documentation folder.

Use the hwclock utility to test RTC. The RTC device node created is /dev/rtc0. If RTC is properly setup hwclock will return non-zero time which is updated per second.

EVM On-Board Components Drivers

AM335x EVM supports components like temperature sensor and ambient light sensor. Usage information on drivers for these components is available in EVM On-Board Components Drivers Guide

Modifying Pin Mux settings

On AM335x devices, the pins are tri-stated and set to Mode 0 or any other mode as required for specific module (e.g., MMC) in U-Boot. If a particular pin needs to be used for any other function than Mode 0 or override any other pin mode which was already set in U-Boot, there are 3 methods to do it.

Method I - Modify Linux Kernel, rebuilt and use

Default mux mode can be changed by adding specific mux entry in the beginning of board_mux array in arch/arm/mach-omap2/board-am335xevm.c or calling omap_mux_init_signal() during initialization (e.g., in device specific initialization function called from omap2_init_devices() in arch/arm/mach-omap2/devices.c).

The names of multiplexed signals are specified in arch/arm/mach-omap2/mux33xx.c file in kernel source directory.

e.g., for setting xref_clk0 pin (mode 0) to usb1_drvvbus (mode 7 or FUNCTION 8), add


to board_mux structure in board file or call

omap_mux_init_signal("xref_clk0.usb1_drvvbus", 0)

The string passed above should be mode0_name.desired_mode_name format.

Method II - Modify pin-mux from arguments passed to Kernel

The above API approach is useful if pin-mux needs to setup at run time depending upon the board/hardware detected without need of maintaining separate kernel binaries. Alternatively, particular pins can be setup by passing respective pinmux details to kernel command line in following format


E.g., to set mmc1_cmd_mux0 (mode 0) pin to gpio0_0 and enable pull down, append following to kernel command line passed from the boot loader:


For pull up (set bit 17):


configuration for multiple pins can be passed which are separated by comma.

For details about this boot parameter, refer Documentation/kernel-parameters.txt in kernel source directory.

Method III - Modify pin-mux from Linux Console

Pin-mux can also be setup from kernel console. This requires debugfs support.

1. Make sure kernel is built with debugfs support Configure the kernel to enable debugfs:

Symbol: DEBUG_FS [=y]
Type  : boolean
Prompt: Debug Filesystem
  Defined at lib/Kconfig.debug:89
    -> Kernel hacking

2. Boot the target hardware and mount debugfs:

mkdir -p /debugfs
mount -t debugfs debugfs /debugfs
cd /debugfs/omap_mux/

3. Assume spi0_d0 pins needs to be set

View current pin-mux setting

root@arago-armv7:/debugfs/omap_mux# cat spi0_d0
name: spi0_d0.gpio0_3 (0x44e10954/0x954 = 0x002f), b NA, t NA
signals: spi0_d0 | uart2_txd | i2c2_scl | NA | NA | NA | NA | gpio0_3

Change pin-mux value (0x20 is an example for MODE 0, Input mode, PULL Enabled with PULL-DOWN mode,

root@arago-armv7:/debugfs/omap_mux# echo 0x20 > spi0_d0

View current pin-mux setting

root@arago-armv7:/debugfs/omap_mux# cat spi0_d0
name: spi0_d0.spi0_d0 (0x44e10954/0x954 = 0x0020), b NA, t NA
signals: spi0_d0 | uart2_txd | i2c2_scl | NA | NA | NA | NA | gpio0_3

Another example (0x31 is an example for MODE 1, Input mode, PULL Enabled with PULL-UP mode,

root@arago-armv7:/debugfs/omap_mux# echo 0x31 > spi0_d0

View current pin-mux setting

root@arago-armv7:/debugfs/omap_mux# cat spi0_d0
name: spi0_d0.uart2_txd (0x44e10954/0x954 = 0x0031), b NA, t NA
signals: spi0_d0 | uart2_txd | i2c2_scl | NA | NA | NA | NA | gpio0_3

Clock Management details

Clock tree from debugfs

Details of clocks such as rate,usecount and flags can be viewed through debugfs entries of the clocks. To access these details one has to mount the debugfs root directory first,follow the steps below to mount debugfs and view clock details:

 make ARCH=arm CROSS_COMPILE=arm-arago-linux-gnueabi- menuconfig
 Select Power management options -> Power Management Debug Support
  • Ensure that Kernel hacking -> Debug Filesystem is selected in Kernel configuration (by default it is selected)
  • Mount the debugfs filesystem
 $ mount -t debugfs none /sys/kernel/debug 
  • Change to clock directory under debugfs,clock entries arranged exactly same as clock tree, ie. root clock -> child clock & sibling clocks, to see the details,

example 1:

 $ cd /sys/kernel/debug/clock
root@arago-armv7:/sys/kernel/debug/clock# ls -l
drwxr-xr-x    5 root     root            0 Jan  1  1970 clk_32768_ck
drwxr-xr-x    6 root     root            0 Jan  1  1970 clk_rc32k_ck
drwxr-xr-x    2 root     root            0 Jan  1  1970 ehrpwm0_tbclk
drwxr-xr-x    2 root     root            0 Jan  1  1970 ehrpwm1_tbclk
drwxr-xr-x    2 root     root            0 Jan  1  1970 ehrpwm2_tbclk
-r--r--r--    1 root     root            0 Jan  1  1970 summary
drwxr-xr-x    2 root     root            0 Jan  1  1970 tclkin_ck
drwxr-xr-x    2 root     root            0 Jan  1  1970 virt_19_2m_ck
drwxr-xr-x    3 root     root            0 Jan  1  1970 virt_24m_ck
drwxr-xr-x    2 root     root            0 Jan  1  1970 virt_25m_ck
drwxr-xr-x    2 root     root            0 Jan  1  1970 virt_26m_ck

example 2:

root@arago-armv7:~# cd /sys/kernel/debug/clock/
root@arago-armv7:/sys/kernel/debug/clock# ls
clk_32768_ck   ehrpwm1_tbclk  tclkin_ck      virt_25m_ck
clk_rc32k_ck   ehrpwm2_tbclk  virt_19_2m_ck  virt_26m_ck
ehrpwm0_tbclk  summary        virt_24m_ck
root@arago-armv7:/sys/kernel/debug/clock# cd clk_32768_ck/
root@arago-armv7:/sys/kernel/debug/clock/clk_32768_ck# ls
flags             rtc_fck           timer1_fck
rate              sysclkout_pre_ck  usecount
root@arago-armv7:/sys/kernel/debug/clock/clk_32768_ck# cat rate
root@arago-armv7:/sys/kernel/debug/clock/clk_32768_ck# cat usecount

Parent change

Currently changing a parent clock is not supported through clk, this can be done from uboot command prompt as below:

  • Load uboot, wait for 1st stage to complete.
  • Interrupt the autoboot of 2nd stage (countdown from 3-0).
  • Find the clocksel register corresponding to the clk whose parent needs to be changed.
  • write the value corresponding to new parent to the register

To write to a reg:

# mw 0x481c50c4 0x3

To read from a reg:

# md 0x481c50c4 1

for help:

# help

Set rate support

Some clocks support changing clock rate dynamically at runtime, clock rate of a clock may be changed only if:

  • The clock is not used by any module or none of its child clock is in use.i.e. clk->usecount is zero.
  • When setting the rate of a leaf clock, parent is not in use i.e.parent->usecount is zero.
  • Changing the clock rate will not cause system unstability.
    To change a clock's rate:
    1.Get the pointer to clk struct by,
clk = clk_get(dev_id,clk_name);

2. Set the new rate,

   ret = clk->set_rate(clk);