libertas SPI Interface and the GPIO / chipselect issue
Sebastian Andrzej Siewior
bigeasy at linutronix.de
Wed May 27 04:11:11 EDT 2009
David Brownell wrote:
> The requirement for any SPI controlller driver in Linux is that it
> hold the chipselect active for the entire spi_message ... with a
> small exception that kicks in if cs_change is set. (That allows
> one message to package a group of transfers, each of which needs
> to be terminated by chip de-select and all of which need to be
> completed in sequence, as a group.)
> That's a basic definitional thing. If there's a hardware notion
> of chipselect that doesn't work that way, it must not be used.
> It's usually easy enough to just use a GPIO.
> Deactivating chipselect is a protocol operation, and it must not be
> done except at clearly defined moments.
thanks for the info David.
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