Re: [spi-devel-general] Re: question on spi_bitbang
From: Kumar Gala
Date: Fri Mar 31 2006 - 14:58:15 EST
On Mar 31, 2006, at 1:32 PM, David Brownell wrote:
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 controllers capable so if/when we have something at a higher
level I can look at adding support for it.
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. :)
Makes sense about needing to set polarity in the chipselect() before
the actual chip select. I just now completely confused on when I
need to things.
My confusion is about the order of which various things occur. setup
(), chipselect() and transfer() vs what's happening in bitbang_work
(). I don't see how we handle the fact that two different devices
may require setup() to be called when we switch between them.
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.
I'm not sure I understand what you'd like to see go into 2.6.17.
- kumar
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