This adds an spi master mode driver via bitbanged gpio. Only syncronous
transfers are implemented. Clock signal timing is accomplished via busy
waits, the gpios are manipulated via the standard gpio interface; these
two factors limit the frequency at which it can operate - but here
a simple and generic implementation was chosen over performance.
The driver supports the various clock polarity and phase
configurations, and can also work with word sizes which are non
multiples of 8bits, currently up to 16 bits.
A sample program is also added demonstrating basic use of the driver
with 9bit data words.
Signed-off-by: Marc Reilly <marc@cpdesign.com.au>
Marc Reilly