UM0851 datasheet(133/245 Pages) STMICROELECTRONICS

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UM0851

Non-volatile memory device drivers

Doc ID 16604 Rev 2

133/245

MTD device nodes

MTD is neither a block nor a char device. There are translations (Flash translation layers or

FTLs) to use them, as if they were.

Instead, the MTD device:

●

Consists of eraseblocks

●

Maintains 3 main operations: read from eraseblock, write to eraseblock, and erase

eraseblock

●

Bad eraseblocks are not hidden and should be dealt with in software

Two popular user modules that enable access to Flash are character device nodes and

block device nodes. Character device nodes provide raw character access to the Flash,

while block device nodes project the Flash as a normal block device, on which a file system

can be created. The devices associated with character device nodes are /dev/mtd0, mtd1,

mtd2 (etc.), while the devices associated with block device nodes are /dev/mtdblock0,

mtdblock1 (etc). Since block device nodes provide block-device-like emulation, it is often

preferable to use file systems like YAFFS/JFFS2 over this emulation.

You can find the list of MTD device nodes below:

# cat /proc/mtd

dev:

size

erasesize

name

mtd0: 00010000 00010000 "XLoader"

mtd1: 00040000 00010000 "UBoot"

mtd2: 002c0000 00010000 "Kernel"

mtd3: 004f0000 00010000 "Root File system"

mtd4: 00010000 00004000 "XLoader"

mtd5: 00050000 00004000 "Uboot"

mtd6: 00400000 00004000 "Kernel"

mtd7: 03ba0000 00004000 "Root File system"

# ls /dev/mtd* -l

crw-rw----

1 0

90,

0 Jan

1 00:00 /dev/mtd0

crw-rw----

1 0

90,

2 Jan

1 00:00 /dev/mtd1

crw-rw----

1 0

90,

4 Jan

1 00:00 /dev/mtd2

crw-rw----

1 0

90,

6 Jan

1 00:00 /dev/mtd3

crw-rw----

1 0

90,

8 Jan

1 00:00 /dev/mtd4

crw-rw----

1 0

90,

10 Jan

1 00:00 /dev/mtd5

crw-rw----

1 0

90,

12 Jan

1 00:00 /dev/mtd6

crw-rw----

1 0

90,

14 Jan

1 00:00 /dev/mtd7

brw-rw----

1 0

31,

0 Jan

1 00:00 /dev/mtdblock0

brw-rw----

1 0

31,

1 Jan

1 00:00 /dev/mtdblock1

brw-rw----

1 0

31,

2 Jan

1 00:00 /dev/mtdblock2

brw-rw----

1 0

31,

3 Jan

1 00:00 /dev/mtdblock3

brw-rw----

1 0

31,

4 Jan

1 00:00 /dev/mtdblock4

brw-rw----

1 0

31,

5 Jan

1 00:00 /dev/mtdblock5

brw-rw----

1 0

31,

6 Jan

1 00:00 /dev/mtdblock6

brw-rw----

1 0

31,

7 Jan

1 00:00 /dev/mtdblock7

Raw mode usage from user space

Raw mode means accessing NAND via MTD layer without using file systems. MTD utils can

be used to access NAND Flash directly without file system. MTD utils uses nodes such as

/dev/mtdX or /dev/mtdblockX and operates using IOCTL calls.

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