[flashrom] SPI status register writes

[Daniel Lenski]

On Mon, 2010-07-26 at 22:27 +0200, Carl-Daniel Hailfinger wrote:
> > 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.
> >   
> 
> Good point. RDSR checking would definitely work here.

The AMICs don't seem to support the continuous repeated reading of the
status register, so they would require cycles of delay-and-poll in any
case.

> > 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?
> >   
> 
> Yes, but I'm not sure if "must be continually clocked out" means that we
> may run RDSR only once, but we can continue reading the response for
> thousands of cycles until RDY/BSY is 0. In that case the exercise would
> be rather pointless and a timer would be the only chance.

Yeah, it's an odd phrasing.

How does flashrom handle this after page program or erase?  The
datasheet indicates that the same behavior applies in terms of waiting
for RDY/BSY after page program, or erase, or WRSR.

> What about delay-then-RDSR?

Repeated until RDSR indicates no more write-in-progress, I presume?
Sounds like the safest combination.

Dan