Messages in this thread | | | From | David Brownell <> | Subject | Re: question on spi_bitbang | Date | Fri, 31 Mar 2006 10:11:00 -0800 |
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On Friday 31 March 2006 9:31 am, Kumar Gala wrote: > I'm looking at using spi_bitbang for a SPI driver and was trying to > understand were the right point is to handle MODE switches. > > There are 4 function pointers provided for each mode.
That's if you are indeed "bit banging", or your controller is the type that's basically a wrapper around a shift register: each txrx_word() function transfers (or bitbangs) a 1-32 bit word in the relevant SPI mode (0-3).
There's also a higher level txrx_bufs() routine for buffer-at-a-time access, better suited to DMA, FIFOs, and half-duplex hardware.
> My controller > HW has a mode register which allows setting clock polarity and clock > phase. I assume what I want is in my chipselect() function is to set > my mode register and have the four function pointers set to the same > function.
I don't know how your particular hardware works, but if you have a real SPI controller it would probably be more natural to have your setup() function handle that mode register earlier, out of the main transfer loop ... unless that mode register is shared among all chipselects, in which case you'd use the setup_transfer() call for that, inside the transfer loop. (That call hasn't yet been merged into the mainline kernel yet; it's in the MM tree.)
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.
- Dave
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