UM0851 datasheet(125/245 Pages) STMICROELECTRONICS

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UM0851

Non-volatile memory device drivers

Doc ID 16604 Rev 2

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The NAND device driver supports various NAND Flash chips. All NAND devices are enlisted

in drivers/mtd/nand/nand_ids.c. If a new NAND device is added in the system, then its

details must be entered here. Here is a code-snippet of 'nand_ids.c'.

Chip ID list

------------

Name, ID code, pagesize, chipsize in MegaByte, eraseblock size, options

struct nand_flash_dev nand_flash_ids[] = {

{"NAND 1MiB 5V 8-bit",

0x6e, 256, 1, 0x1000, 0},

{"NAND 2MiB 5V 8-bit",

0x64, 256, 2, 0x1000, 0},

{"NAND 64MiB 1,8V 16-bit",

0x46, 512, 64, 0x4000, NAND_BUSWIDTH_16},

{"NAND 64MiB 1,8V 8-bit",

0xA2, 0,

64, 0, LP_OPTIONS},

{"NAND 64MiB 3,3V 8-bit",

0xF2, 0,

64, 0, LP_OPTIONS},

{"NAND 64MiB 1,8V 16-bit",

0xB2, 0,

64, 0, LP_OPTIONS16},

{"NAND 64MiB 3,3V 16-bit",

0xC2, 0,

64, 0, LP_OPTIONS16},

{NULL,}

}

5.1.3

NAND device driver overview

This section decribes the Linux MTD framework.

MTD overview

MTD is a generic subsystem for handling memory technology devices under Linux. MTD

provides a generic interface between the device drivers and the upper layers of the system.

Device drivers do not need to know about the storage formats used, such as FTL, FFS2,

etc. They only need to provide simple routines for read, write and erase. The presentation of

the device's contents to the user in an appropriate form will be handled by the upper layers

of the system.

The MTD system is divided into two types of module: "users" and "drivers". Drivers are the

modules which provide raw read/write/erase access to physical memory devices. Users are

like YAFFS or JFFS (as shown in figure above), they are the modules which use MTD

drivers and provide a higher-level interface to the user space.

JFFS is a file system which runs directly on the Flash, and MTDBLOCK performs no

translation - just provides a block device interface directly to the underlying MTD driver.

NAND device driver interface to MTD

The NAND device driver allocates a struct mtd_info with information about the NAND Flash

device and pointers to access routines at the time of initialization. Some important fields of

the struct mtd_info are described below.

struct mtd_info {

char name[32];

Name of the device. Rarely used, but presented to

the user via the /proc/mtd interface.

u_char type;

Type of memory technology used in this device. Choose

from:

u_long flags;

Device capabilities. Bitmask. Choose from:

Such as Direct IO is possible, eXecute-In-Place

possible, Out-of-band data (NAND flash) and Device

capable of automatic ECC

loff_t size;

Total size in bytes.

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