[alsa-devel] Reasonable sound hardware parameters?

[Jaroslav Kysela]

On Sat, 26 May 2007, Joachim Förster wrote:

> Hi ALSA devs,
> 
> as I already described in one of my last posts on the list, I'm going to
> write a ALSA driver for a sound controller which will also be "written"
> at the same time (VHDL for FPGA) - on top of an embedded system (Xilinx
> ML403 EvalBoard, PowerPC 405). We will do playback feature only.
> 
> The point is, that we will have _no_ real DMA and we don't want to use
> the copy/silence or ack/workqueue (with intermediate buffer). So we
> decided to move the ring buffer, which usually exists in RAM into the
> sound controller and handle it as some kind of device IO memory, which
> should be mmap'able (kernel function io_remap_pfn_range()). So, the
> important goal is, to have mmap feature in the ALSA driver.
> 
> First question: To implement mmap on such kind of device IO memory, I
> have to use snd_pcm_lib_mmap_iomem() as mmap() callback - like it is
> used in the rme32 driver, right?

Yes. rme32 is quite similar.

> Second question: Do the following parameters make sense regarding the
> size of the HW ring buffer and period sizes:
> 
> .buffer_bytes_max=16*1024;
> .period_bytes_max=8*1024;
> .period_bytes_min=?? resonable value ??

32 or 64

> .periods_min=2;
> .periods_max=?? resonable value ??

16

> Furthermore, the sound controller will fire an interrupt after one 
> period is played. Are there any arguments against these values? Any 
> comments?

Yes, I think that the access through a PCI I/O window to a PCI device is 
much slower than PCI DMA transfers with bursts. I would really consider to 
design hardware with real DMA. Of course, if it's only experimental stuff, 
then don't worry.

						Jaroslav

-----
Jaroslav Kysela <perex at suse.cz>
Linux Kernel Sound Maintainer
ALSA Project, SUSE Labs