TS-7670 NAND Controller

The NAND on the i.MX286 is a 2GiB part attached directly to the CPU. The kernel handles the NAND through its MTD drivers.

Instead of a traditional flash filesystem (JFFS2 for example) the i.MX286 implements UBI and UBIFS.

UBI and UBIFS

UBI is the Unsorted Block Images layer, and is an erase block management layer. UBI serves two purposes, tracking NAND bad blocks and providing wear leveling. While it is possible to run a traditional flash filesystem on top of UBI, it is not recommended. UBIFS was written with UBI in mind and is able to take full advantage of what UBI provides. UBIFS has multiple advantages over JFFS2, UBIFS supports write caching, UBIFS performs better on larger NAND devices, mounts faster, allows for quicker access to large files, improved write speeds, and indexes stored in flash not in system memory.

Using UBI and UBIFS

UBI is implemented directly on top of linux's MTD subsystem, the first thing necessary is to format the device for UBI to use.

ubiformat /dev/mtd1 #This will prepare /dev/mtd1 to accept UBI and is mindful of UBIs erase counters

After this, the device must be attached to UBI

ubiattach -m 1

This will attach the device to the UBI subsystem. Doing this will create a /dev/ubi0 device node that represents the entire UBI device. A UBI attach does take longer on larger MTD devices.

Once this is done, at least one volume must be made. There are two types of volumes, static and dynamic. A dynamic volume is liken to a standard filesystem, it creates and uses a UBIFS filesystem. A static volume is meant to be run right on top of UBI, and does not use UBIFS. It is meant for smaller volumes with blobs of configuration data, and is protected with CRC32s. While it is possible, it is not wise to use UBIFS on top of a static volume, it will result in a much slower device since since both UBI and UBIFS will be implementing CRC32s.