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AM335x NAND Driver's Guide
Contents
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
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