FLASH(3)                                                 FLASH(3)

     NAME
          flash - flash memory

     SYNOPSYS
          bind -a #F[n] /dev
9          /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 deci-
          mal 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 val-
          ues, 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

9

     FLASH(3)                                                 FLASH(3)

          characteristics 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 char-
          acteristics of each group of erase units within the parti-
          tion, 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 par-
                    ent 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 manu-
                    facturer might also have locked the flash in hard-
                    ware, 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)

     FLASH(3)                                                 FLASH(3)

     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.