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MTD

mtd is a utility we use to write to an MTD (Memory Technology Device). Please read the Notes to learn more.

Invocation

Usage: mtd [<options> ...] <command> [<arguments> ...] <device>[:<device>...]

Writing to MTD

`unlock <dev>`	unlock the device
`refresh <dev>`	refresh mtd partition
`erase <dev>`	erase all data on device
`write <imagefile>\|-`	write <imagefile> (use - for stdin) to device
`jffs2write <file>`	append <file> to the jffs2 partition on the device
`fixtrx <dev>`	fix the checksum in a trx header on first boot

Options

`-q`	quiet mode (once: no [w] on writing, twice: no status messages)
`-n`	write without first erasing the blocks
`-r`	reboot after successful command
`-f`	force write without trx checks
`-e <device>`	erase <device> before executing the command
`-d <name>`	directory for jffs2write, defaults to “tmp”
`-j <name>`	integrate <file> into jffs2 data when writing an image
`-o offset`	offset of the image header in the partition(for fixtrx)
`-F <part>[:<size>[:<entrypoint>]][,<part>...]`	alter the fis partition table to create new partitions replacing the partitions provided as argument to the write command (only valid together with the write command)

Examples

Download linux.bin from Internet (it's not safe to do so, here is for demonstration purpose only), then write linux.bin to a MTD partition labeled as linux (could be mtd4) and reboot afterwards:

cd /tmp
wget http://www.example.org/linux.bin
mtd -r write /tmp/linux.bin linux

Example (flash u-boot from OpenWrt)

Tested on Marvell EspressoBinBoard based on MVEBU, (see forum topic) Download flash-image.bin for your specific hardware from SnapShots

You can checks your mtd partitions from proc :

root@EBIN:~# cat /proc/mtd 
dev:    size   erasesize  name
mtd0: 003f0000 00010000 "firmware"
mtd1: 00010000 00010000 "u-boot-env"

(it's not safe to do so, here is for demonstration purpose only),

then write flash-image.bin to a MTD partition labeled as spi0.0 (could be mtd0 or firmware) and reboot afterwards :

cd /tmp
wget https://downloads.openwrt.org/snapshots/targets/mvebu/cortexa53/trusted-firmware-a-espressobin-v7-1gb/flash-image.bin
mtd -r write /tmp/flash-image.bin /dev/mtd0

mtd vs dd

The differences between dd (disc dump) and mtd are ... TODO

mtd on vendor-firmware

mtd can even be used with vendor-firmware, as long as the kernel had mtd-support and not using something “home-brewed”. When the vendor is not shipping the binary it can probably transferred via scp, netcat, tftp, ftp, httponto the board. The original binary from the OpenWrt-package might not run on the vendor-os, but linking it static should do the trick. With OpenWrt-21.02 I was using a small hack to to let the buildroot create a static binary:

sed -i -e "s/^LDFLAGS += /LDFLAGS += -static /" package/system/mtd/src/Makefile
make package/mtd/compile

This patches the mtd source to include the “-static” option when building the binary. This way the binary gets all dependent library-code embedded to make it run itself, as long as the correct CPU-target is used. The new binary can be extracted from the resulting package or just copied from build_dir/target-<ARCH>/linux-<TARGET>-<SUBTARGET>/mtd.

Notes

Flash memory - things to consider
MTD (Memory Technology Device)
documentation on MTDs.
The differences between flash devices and block drives in a table
To make it more clear, here is a small comparison of MTD devices and block devices:
- MTD devices represent flash devices and they consist of eraseblocks of rather large size, typically about 128KiB. Block devices consist of small blocks, typically 512 bytes. MTD devices support 3 main operations - read from some offset within an eraseblock, write to some offset within an eraseblock, and erase a whole eraseblock. Block devices support 2 main operations - read a whole block and write a whole block.
- The whole eraseblock has to be erased before it becomes possible to re-write its contents. Blocks may be just re-written.
- Eraseblocks become worn out after some number of erase cycles - typically 100K-1G for SLC NAND and NOR flashes, and 1K-10K for MLC NAND flashes. Blocks do not have the wear-out property.
- Eraseblocks may become bad (only on NAND flashes) and software should deal with this. Blocks on hard drives typically do not become bad, because hardware has mechanisms to substitute bad blocks, at least in modern LBA disks.
Sometimes flash memory uses FTL: Raw Flash vs. FTL (Flash Translation Layer)
Although most flashes on the commodity hardware have FTL, there are systems which have bare flashes and do not use FTL! Those are mostly various handheld devices and embedded systems.

Table of Contents

MTD