doc/README.nand

NAND FLASH commands and notes


See NOTE below!!!


# (C) Copyright 2003
# Dave Ellis, SIXNET, dge@sixnetio.com
#
# See file CREDITS for list of people who contributed to this
# project.
#
# This program is free software; you can redistribute it and/or
# modify it under the terms of the GNU General Public License as
# published by the Free Software Foundation; either version 2 of
# the License, or (at your option) any later version.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with this program; if not, write to the Free Software
# Foundation, Inc., 59 Temple Place, Suite 330, Boston,
# MA 02111-1307 USA

Commands:

   nand bad
      Print a list of all of the bad blocks in the current device.

   nand device
      Print information about the current NAND device.

   nand device num
      Make device `num' the current device and print information about it.

   nand erase off size
   nand erase clean [off size]
      Erase `size' bytes starting at offset `off'.  Only complete erase
      blocks can be erased.

      If `clean' is specified, a JFFS2-style clean marker is written to
      each block after it is erased. If `clean' is specified without an
      offset or size, the entire flash is erased.

      This command will not erase blocks that are marked bad. There is
      a debug option in cmd_nand.c to allow bad blocks to be erased.
      Please read the warning there before using it, as blocks marked
      bad by the manufacturer must _NEVER_ be erased.

   nand info
      Print information about all of the NAND devices found.

   nand read addr ofs size
      Read `size' bytes from `ofs' in NAND flash to `addr'. If a page
      cannot be read because it is marked bad or an uncorrectable data
      error is found the command stops with an error.

   nand read.jffs2 addr ofs size
      Like `read', but the data for blocks that are marked bad is read as
      0xff. This gives a readable JFFS2 image that can be processed by
      the JFFS2 commands such as ls and fsload.

   nand read.oob addr ofs size
      Read `size' bytes from the out-of-band data area corresponding to
      `ofs' in NAND flash to `addr'. This is limited to the 16 bytes of
      data for one 512-byte page or 2 256-byte pages. There is no check
      for bad blocks or ECC errors.

   nand write addr ofs size
      Write `size' bytes from `addr' to `ofs' in NAND flash. If a page
      cannot be written because it is marked bad or the write fails the
      command stops with an error.

   nand write.jffs2 addr ofs size
      Like `write', but blocks that are marked bad are skipped and the
      is written to the next block instead. This allows writing writing
      a JFFS2 image, as long as the image is short enough to fit even
      after skipping the bad blocks. Compact images, such as those
      produced by mkfs.jffs2 should work well, but loading an image copied
      from another flash is going to be trouble if there are any bad blocks.

   nand write.oob addr ofs size
      Write `size' bytes from `addr' to the out-of-band data area
      corresponding to `ofs' in NAND flash. This is limited to the 16 bytes
      of data for one 512-byte page or 2 256-byte pages. There is no check
      for bad blocks.

Configuration Options:

   CFG_CMD_NAND
      A good one to add to CONFIG_COMMANDS since it enables NAND support.

   CONFIG_MTD_NAND_ECC_JFFS2
      Define this if you want the Error Correction Code information in
      the out-of-band data to be formatted to match the JFFS2 file system.
      CONFIG_MTD_NAND_ECC_YAFFS would be another useful choice for
      someone to implement.

   CFG_MAX_NAND_DEVICE
      The maximum number of NAND devices you want to support.

NAND Interface:

   #define NAND_WAIT_READY(nand)
      Wait until the NAND flash is ready. Typically this would be a
      loop waiting for the READY/BUSY line from the flash to indicate it
      it is ready.

   #define WRITE_NAND_COMMAND(d, adr)
      Write the command byte `d' to the flash at `adr' with the
      CLE (command latch enable) line true. If your board uses writes to
      different addresses to control CLE and ALE, you can modify `adr'
      to be the appropriate address here. If your board uses I/O registers
      to control them, it is probably better to let NAND_CTL_SETCLE()
      and company do it.

   #define WRITE_NAND_ADDRESS(d, adr)
      Write the address byte `d' to the flash at `adr' with the
      ALE (address latch enable) line true. If your board uses writes to
      different addresses to control CLE and ALE, you can modify `adr'
      to be the appropriate address here. If your board uses I/O registers
      to control them, it is probably better to let NAND_CTL_SETALE()
      and company do it.

   #define WRITE_NAND(d, adr)
      Write the data byte `d' to the flash at `adr' with the
      ALE and CLE lines false. If your board uses writes to
      different addresses to control CLE and ALE, you can modify `adr'
      to be the appropriate address here. If your board uses I/O registers
      to control them, it is probably better to let NAND_CTL_CLRALE()
      and company do it.

   #define READ_NAND(adr)
      Read a data byte from the flash at `adr' with the
      ALE and CLE lines false. If your board uses reads from
      different addresses to control CLE and ALE, you can modify `adr'
      to be the appropriate address here. If your board uses I/O registers
      to control them, it is probably better to let NAND_CTL_CLRALE()
      and company do it.

   #define NAND_DISABLE_CE(nand)
      Set CE (Chip Enable) low to enable the NAND flash.

   #define NAND_ENABLE_CE(nand)
      Set CE (Chip Enable) high to disable the NAND flash.

   #define NAND_CTL_CLRALE(nandptr)
      Set ALE (address latch enable) low. If ALE control is handled by
      WRITE_NAND_ADDRESS() this can be empty.

   #define NAND_CTL_SETALE(nandptr)
      Set ALE (address latch enable) high. If ALE control is handled by
      WRITE_NAND_ADDRESS() this can be empty.

   #define NAND_CTL_CLRCLE(nandptr)
      Set CLE (command latch enable) low. If CLE control is handled by
      WRITE_NAND_ADDRESS() this can be empty.

   #define NAND_CTL_SETCLE(nandptr)
      Set CLE (command latch enable) high. If CLE control is handled by
      WRITE_NAND_ADDRESS() this can be empty.

More Definitions:

   These definitions are needed in the board configuration for now, but
   may really belong in a header file.
   TODO: Figure which ones are truly configuration settings and rename
	 them to CFG_NAND_... and move the rest somewhere appropriate.

   #define SECTORSIZE 512
   #define ADDR_COLUMN 1
   #define ADDR_PAGE 2
   #define ADDR_COLUMN_PAGE 3
   #define NAND_ChipID_UNKNOWN 0x00
   #define NAND_MAX_FLOORS 1
   #define NAND_MAX_CHIPS 1


NOTE:
=====

We now use a complete rewrite of the NAND code based on what is in
2.6.12 Linux kernel.

The old NAND handling code has been re-factored and is now confined
to only board-specific files and - unfortunately - to the DoC code
(see below). A new configuration variable has been introduced:
CFG_NAND_LEGACY, which has to be defined in the board config file if
that board uses legacy code. If CFG_NAND_LEGACY is defined, the board
specific config.mk file should also have "BOARDLIBS =
drivers/nand_legacy/libnand_legacy.a". For boards using the new NAND
approach (PPChameleon and netstar at the moment) no variable is
necessary, but the config.mk should have "BOARDLIBS =
drivers/nand/libnand.a".

The necessary changes have been made to all affected boards, and no
build breakage has been introduced, except for NETTA and NETTA_ISDN
targets from MAKEALL. This is due to the fact that these two boards
use JFFS, which has been adopted to use the new NAND, and at the same
time use NAND in legacy mode. The breakage will disappear when the
board-specific code is changed to the new NAND.

As mentioned above, the legacy code is still used by the DoC subsystem.
The consequence of this is that the legacy NAND can't be removed  from
the tree until the DoC is ported to use the new NAND support (or boards
with DoC will break).