```

     FLASH(3)						      FLASH(3)

     NAME
	  flash	- flash	memory

     SYNOPSIS
	  bind -a #F[n]	/dev
	  /dev/flash
	  /dev/flash/part
	  /dev/flash/partctl

     DESCRIPTION
	  The flash memory device serves a two-level directory,	giving
	  access to files representing part or all of a	bank of	flash
	  memory.  A platform might have more than one bank of flash,
	  numbered starting from 0.  The attach	specifier n is a
	  decimal integer that selects a particular bank of flash
	  (default: 0).	 Both NOR and NAND flash is supported.	For
	  both types of	flash, the driver gives	a read/write/erase
	  interface to the raw flash device, which can impose con-
	  straints on operations beyond	those imposed by the driver.

	  The top level	directory contains a single directory named
	  flash	for bank 0, and	flashn for each	other bank n. It con-
	  tains	two files for each partition: a	data file part and an
	  associated control file partctl, where part is the name of
	  the partition.  Each partition represents a region of	flash
	  memory that starts and ends on a flash segment (erase	unit)
	  boundary.  The system	initially creates a single standard
	  partition flash representing the whole of flash memory, and
	  the corresponding control file flashctl.  Other partitions
	  can be created by writing to flashctl	as described below.

	  The data file	part provides read and write access to the
	  bytes	on the system's	flash memory.  Bytes can be read and
	  written on any byte boundary:	the interface hides any	align-
	  ment restrictions.  A	read returns the value of the bytes at
	  the current file offset, where zero is the start of the par-
	  tition.  A write reprograms the flash	to the given byte
	  values, at the current file offset (relative to the start of
	  the partition), using	the physical device's reprogramming
	  algorithm.  An erased	flash byte is logically	0xFF (regard-
	  less of the conventions of the physical flash	device).  A
	  write	can change a bit with value 1 to a 0, but cannot
	  change a 0 bit to 1; that can	only be	done by	erasing	one or
	  more flash segments.	NAND flash typically has restrictions
	  on the number	of writes allowed to a page before requiring a
	  block	erase.

	  The control file partctl can be read and written.  A read
	  returns several lines	containing decimal and hexadecimal
	  numbers (separated by	white space) revealing the charac-
	  teristics of memory within the partition.  The first line
	  gives	the manufacturer ID,  the flash	device ID, the memory
	  width	in bytes, and a	string giving the flash	type
	  (currently either nor	or nand).  Subsequent lines give
	  characteristics of each group	of erase units within the par-
	  tition, where	the erase units	within a group have the	same
	  properties.  Each line gives the start and end (as byte
	  addresses) of	the erase units	in the region that lie within
	  the partition, followed by the size in bytes of each erase
	  unit,	which is followed for NAND flash by the	size in	bytes
	  of a page.  The sizes	for NAND flash include the extra bytes
	  per page typically used to hold an ECC and block status.  A
	  write	contains one of	the following textual commands:

	  add name start end
		    Create a new partition that	ranges from start to
		    end	within the current partition.  Each value must
		    be numeric (decimal, octal or hexadecimal) and a
		    multiple of	the erase unit size.  Name must	not be
		    the	name of	an existing partition.	On success,
		    new	files name and namectl will appear in the
		    parent flash directory.
	  erase	all Erase the whole flash partition, setting all bytes
		    to 0xFF, except those that are hardware write-
		    protected.
	  erase	offset
		    Erase the segment that begins at the given offset
		    within the partition, setting all bytes to 0xFF,
		    except those that are hardware write-protected.
		    The	offset is given	in bytes, but must be a	multi-
		    ple	of the segment (erase unit) size.
	  protectboot [	off ]
		    By default the system prevents erase unit 0	of the
		    flash from being erased or written,	assuming it
		    contains the primary bootstrap.  Writing this com-
		    mand with parameter	off removes that protection.
		    Writing protectboot	with any other parameter (or
		    none) restores the protection.  Note that a
		    manufacturer might also have locked	the flash in
		    hardware, and that protection must be removed in a
		    device-dependent way.
	  sync	    If the underlying device must buffer or cache
		    (current devices do	not), flush the	buffer(s).

	  The syntax of	all numbers is that of strtoul (in atof(2));
	  the default base is 10.

     SOURCE
	  /sys/src/9/*/devflash.c

     SEE ALSO
	  flashfs(4), paqfs(4)

     DIAGNOSTICS
	  A write will return an error if an attempt is	made to	change
	  a 0 bit to 1,	or if the flash	memory fails to	be programmed
	  correctly.

     BUGS
	  The flash cannot be written if the kernel is executing
	  directly from	flash, because the physical flash cannot be
	  read during programming, and the driver does not copy	the
	  programming code to DRAM.

```