On Thu, Jan 19, 2012 at 06:49:25PM +0100, Linus Walleij wrote: > On Wed, Jan 18, 2012 at 1:30 PM, Russell King - ARM Linux > <li...@arm.linux.org.uk> wrote: > > On Wed, Jan 18, 2012 at 01:13:29PM +0100, Linus Walleij wrote: > > >> We usually merge drivers for microwire, TI, Motorola ... etc into > >> drivers/spi as well. It's a good enough fit, the differences are very > >> small. This is how we configure mode from the PL022 driver platform data: > > > > How do you send audio data at 16-bit 2 channel 48kHz continuously with > > the SPI subsystem? > > Can't say because we haven't used it for audio transfers. However > I am pretty convinced that it'd work because we're running a > 20 Mbit data link on that SPI port. > > To get the high data rates we have an internal message queue in > the driver that saturates the SPI port. Sometimes we even start to > run parts of the driver in parallel on two cores: CPU0 is handling > IRQs from the driver while CPU1 is preparing messages to/from > the SPI subsystem.
A SMP system, which SA1100 is not. With audio on the SA1100, we have to keep both DMA transfer buffer pointers filled to ensure that audio does not suffer. I don't see submitting multiple SPI transfers into the SPI subsystem would be able to do that without waiting for the previous transfer to stop completely before starting the next - and that implies the DMA transfer completes before starting to program up the next one. What I'm saying is that SPI will want DMA activity to complete _and_ end before it starts on the next transfer, which is going to create a break in the data output. Given that audio here just requires the SSP to be configured, and then everything else is just DMA, I don't see why we need to waste cycles fiddling with the SPI subsystem with its inherent batching of transfers. ------------------------------------------------------------------------------ Keep Your Developer Skills Current with LearnDevNow! The most comprehensive online learning library for Microsoft developers is just $99.99! Visual Studio, SharePoint, SQL - plus HTML5, CSS3, MVC3, Metro Style Apps, more. Free future releases when you subscribe now! http://p.sf.net/sfu/learndevnow-d2d _______________________________________________ spi-devel-general mailing list spi-devel-general@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/spi-devel-general
