On Thu, 2006-09-14 at 12:29 +0100, Takashi Iwai wrote: > >>> Lee Revell <rlrevell@xxxxxxxxxxx> 09/12/06 10:27 PM >>> > > I have a device here that can play PCM, but it's a weird implementation. > > Only 2 periods of 0x2000 words per buffer are supported, and there is no > > DMA - the driver must poll a status register, and when the chip is > > ready, deliver all 0x2000 words using outw() then send an end xfer > > command. > > > > I think I need to use an intermediate buffer, and implement copy/silence > > callbacks that write to this. Then I plan to use a tasklet or workqueue > > to do the actual xfer of PCM data to the hardware. A timer callback > > will periodically check whether at least 0x2000 words are in the buffer > > and if so, schedule the tasklet to drain it. > > You can implement it in two ways, at least. > > One is to use copy and silent callbacks. This is pretty straightforward, > doesn't need extra buffer, but it cannot use the native mmap. (alsa-lib > provides the mmap emulation mode, but it seems not so stable.) > Also, the buffer and period sizes are very restricitve (in your case, 0x2000 > x 2 words), so many apps might not work well. > An exampleof this type is isa/sb/emu8000_pcm.c (and some of gus pcm, > IIRC). > > Another is to use an intermediate buffer as you suggsted. > In this case, you do _not_ need copy and silent callbacks. These callbacks > are the operations to copy and silent the hardware buffers. WIth an > intermediate buffer, the copy and silent are done on this buffer, i.e. on > normal RAM. What you need instead is the background-running copy > operation from this intermediate buffer to the hardware via outw. > > This copy task could be done in the interrupt handler (or timer in your case) > if it's minimum. If not, it'd be better to take a workq since it can sleep and > much preemptive. Thanks very much for the information. So if I use an intermediate buffer but no copy and silence callbacks, I must copy the data to the hardware in a workqueue (I have no interrupt ability and the copy to hardware must be able to sleep). Where do I copy the data from, and how do I know when 0x2000 words are available? By directly accessing runtime->dma_area and the software pointer? IOW how do I get the information that would be passed to the copy callback? Lee ------------------------------------------------------------------------- Using Tomcat but need to do more? Need to support web services, security? Get stuff done quickly with pre-integrated technology to make your job easier Download IBM WebSphere Application Server v.1.0.1 based on Apache Geronimo http://sel.as-us.falkag.net/sel?cmd=lnk&kid=120709&bid=263057&dat=121642 _______________________________________________ Alsa-devel mailing list Alsa-devel@xxxxxxxxxxxxxxxxxxxxx https://lists.sourceforge.net/lists/listinfo/alsa-devel
