Re: [spi-devel-general] Re: question on spi_bitbang

[David Brownell <david-b@pacbell.net>]

On Friday 31 March 2006 11:07 am, Kumar Gala wrote:
> My controller is just a shift register that I can set the  
> characteristics of (bit length for example, reverse data).

I've got a patch somewhere to enable LSB-first transfers in the API,
though without an implementation, if you're interested.  I'll post it
as an RFC at some point.


> > The chipselect() call should only affect the chipselect signal and,
> > when you're activating a chip, its initial clock polarity.  Though
> > if you're not using the latest from the MM tree, that's also your
> > hook for ensuring that the SPI mode is set up right.
> 
> Why deal with just clock polarity and not clock phase as well in  
> chipselect()?

You could, but the point is that you _must_ set the initial polarity
before setting the chipselect.  Most SPI devices support modes 0 and 3,
and make the choice based on the clock polarity when chipselect goes
active.  Changing polarity later would start a transfer.  :)


> It sounds like with the new patch, I'll end up setting txrx_word[] to  
> the same function for all modes.

Yes, it does sound like that.  If that works for you, I'd like to see
that go into 2.6.17 kernels.

- Dave