FLASH(3) FLASH(3)
NAME
flash - flash memory
SYNOPSYS
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 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.
Other drivers such as ftl(3) or logfs(3) implement any
higher-level format required, including ECC for NAND flash,
for instance.
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 16rFF (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. Reads and writes are unbuffered.
Page 1 Plan 9 (printed 11/22/24)
FLASH(3) FLASH(3)
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 character-
istics of memory within the partition. The first line gives
the the manufacturer ID, the flash device ID, the memory
width in bytes, and a string giving the flash type (cur-
rently either nor or nand). Subsequent lines give charac-
teristics of each group of erase units within the partition,
where the erase units within a group have the same proper-
ties. Each line gives the start and end (as byte addresses)
of the erase units in the region that lie within the parti-
tion, 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 16rFF, 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 16rFF,
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 (cur-
rent devices do not), flush the buffer(s).
The syntax of all numbers is that of strtoul(10.2); the
default base is 10.
SOURCE
Page 2 Plan 9 (printed 11/22/24)
FLASH(3) FLASH(3)
/os/*/devflash.c
/os/*/flash*.c
SEE ALSO
ftl(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.
Page 3 Plan 9 (printed 11/22/24)