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AM335x NAND Driver's Guide

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AM335x NAND Driver's Guide
Linux PSP

Introduction[edit]

The general-purpose memory controller (GPMC) is an unified memory controller dedicated to interfacing external memory devices:

  • Asynchronous SRAM-like memories and application-specific integrated circuit (ASIC) devices
  • Asynchronous, synchronous, and page mode (only available in non-multiplexed mode) burst NOR flash devices
  • NAND Flash
  • Pseudo-SRAM devices


Features[edit]

Hardware Features[edit]

The GPMC can access various external devices through the L3 Slow Interconnect. The flexible programming model allows a wide range of attached device types and access schemes.

The GPMC consists of six blocks:

  • Interconnect port interface
  • Address decoder, GPMC configuration, and chip-select configuration register file
  • Access engine
  • Prefetch and write-posting engine
  • Error correction code engine (ECC)
  • External device/memory port interface

AM335x Memory subsystem.jpg


Software Features[edit]

  • Access 8-bit NAND
  • BCH8 ECC scheme with 8-bit error correction. BCH8 ECC Scheme used to make compatible with all other components (RBL, U-Boot..)
  • Polled Prefetch Mode


AM335x NAND Device Layout[edit]

Layout for NAND flash device is described here.


ECC schemes usage table[edit]

ECC scheme used by different components is described in the table


Driver Configuration[edit]

To enable/disable NAND support, start the Linux Kernel Configuration tool:


host$ make menuconfig 


Select Device Drivers from the main menu.

    ...
    ...
    [ ] Networking support --->
    Device Drivers --->
    File systems --->
    ...
    ...
  • Enable below Configs to enable MTD Support along with MTD nand driver support
Device Drivers  ---> 
  <*> Memory Technology Device (MTD) support  --->
            [*]   Command line partition table parsing
            <*>   Direct char device access to MTD devices
            <*>   Caching block device access to MTD devices
            <*>   NAND Device Support  --->
                        <*>    NAND Flash device on OMAP2 and OMAP3
            <*>   Enable UBI - Unsorted block images  --->

Module Build[edit]

Module build for the NAND driver is supported. To do this, make the changes as below

Device Drivers  ---> 
  <*> Memory Technology Device (MTD) support  --->
            [*]   Command line partition table parsing
            <*>   Direct char device access to MTD devices
            <*>   Caching block device access to MTD devices
            <M>   NAND Device Support  --->
                        <M>    NAND Flash device on OMAP2 and OMAP3
            <*>   Enable UBI - Unsorted block images  --->

For loading modules follow the steps below

      target$ insmod drivers/mtd/nand/nand_ecc.ko 
      target$ insmod drivers/mtd/nand/nand_ids.ko
      target$ insmod drivers/mtd/nand/nand.ko
      target$ insmod drivers/mtd/devices/omap2_elm.ko
      target$ insmod drivers/mtd/nand/omap2.ko

Device Interface[edit]

You always need a pair mtdx/mtdblockx of device nodes to access your flash file system. The mtdx is used to access the raw flash device, the mtdblockx is used to access the disk/block established in the raw flash.

Use MTD-Utils user space tools to access NAND partition from Linux console

Below are some of the examples for accessing NAND partitions

  • Erase the nand partition (assume partition 3)
    target$ flash_eraseall /dev/mtd3
  • write a file to nand partition (assume partition 4)
    target$ nandwrite -p /dev/mtd4 u-boot.img
  • Mount nand partition from U-Boot as Root file system partition for Linux
    u-boot> setenv bootargs 'console=ttyO0,115200n8 root=ubi0:rootfs rw ubi.mtd=<partion_id>,2048 noinitrd rootfstype=ubifs mem=256M rootwait=1'


The value of PARTITION_ID depends on MTD device which holds the root filesystem. The below example assumes UBIFS file system is flashed on MTD partition 7 and respective device is enabled on the board.

    u-boot> setenv bootargs 'console=ttyO0,115200n8 root=ubi0:rootfs rw ubi.mtd=7,2048 noinitrd rootfstype=ubifs mem=256M rootwait=1'



Proc Interface[edit]

The /proc/mtd kernel interface is a status interface. A lot of useful information about the nand system can be found in the /proc/mtd file.

  • Use /proc/mtd to get information on how many partitions are currently configured by the kernels flash driver.
    target$ cat /proc/mtd

You should see output similar to:

    target$ cat /proc/mtd
   dev:    size   erasesize  name
   mtd0: 00020000 00020000 "SPL"
   mtd1: 00020000 00020000 "SPL.backup1"
   mtd2: 00020000 00020000 "SPL.backup2"
   mtd3: 00020000 00020000 "SPL.backup3"
   mtd4: 001e0000 00020000 "U-Boot"
   mtd5: 00020000 00020000 "U-Boot Env"
   mtd6: 00500000 00020000 "Kernel"
   mtd7: 0f880000 00020000 "File System"


AM335x NAND File system support[edit]

On AM335x, JFFS2 support has been super-seeded by UBIFS. JFFS2 support is disabled in default config.

For more information of UBIFS refer UBIFS Support Guide

To enable JFFS2, Refer AM335x JFFS2 Support Guide


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