[flashrom] SPI status register writes

[Daniel Lenski]

On Mon, 2010-07-26 at 20:35 +0200, Carl-Daniel Hailfinger wrote:
> Quite a few SPI flash chips need a few milliseconds to write the status
> register (AT25 series etc.), but we do not take care of this at all. The
> same flash chips ignore any commands sent while the status register
> write cycle is in progress. Given that we execute WRSR once per write, I
> think it is pretty OK to have a 100 ms programmer delay after WRSR. An
> alternative would be to watch the status register contents, but that may
> or may not work, the datasheets are completely unclear about that case.
> If we're lucky, this will even solve a few write/erase issues we were
> seeing.
> 
> What do you think?

Most of the AMIC datasheets explicitly state that bit 0 of the status
register indicates completion of the WRSR operation, e.g. the A25L032
datasheet:

        The Write In Progress (WIP) bit [SR bit 0] is 1 during the
        self-timed Write Status Register cycle, and is 0 when it is
        completed. When the cycle is completed, the Write Enable Latch
        (WEL) is reset.

The AT25DF021 datasheet states this more generally:

        The RDY/BSY bit [SR bit 0] is used to determine whether or not
        an internal operation, such as a program or erase, is in
        progress. To poll the RDY/BSY bit to detect the completion of a
        program or erase cycle, new Status Register data must be
        continually clocked out of the device until the state of the
        RDY/BSY bit changes from a logical "1" to a logical "0".

Presumably "an internal operation" includes WRSR?

Dan