At Mon, 27 Nov 2006 19:28:38 +0100, Jonas Eymann wrote: > > > > At Wed, 22 Nov 2006 10:44:55 +0100, > > Jonas Eymann wrote: > > > > > > Hi everyone, > > > > > > I'm currently developing/ enhancing an ALSA driver for a Silicon > > > Motion SM501 compagnion chip which contains also an 8051 µC acting > > > as AC97 controller. It doesn't support DMA and so the copy of audio > > > data is done in the driver. There is a small hardware buffer of 1920 > > > bytes which is devided into two halves and used as ring buffer. When > > > the hardware has finished playing one half, it sends an interrupt to > > > the driver so it can fill this half with new audio data while the > > > hardware plays from the other one and so on. In the driver, I use an > > > intermediate buffer with vmalloc(). > > > > > > Actually, I have a working driver now, but one small problem remains > > > and I'm absolutely running out of ideas how to fix it: when the > > > playback starts, the hardware expects the buffer to be filled > > > completely (both halves), but the copy routine which does this first > > > filling (snd_sm501_pfill()) only gets one period, not the two which > > > are needed to fill the buffer completely. The second half it just > > > reads zeros. It seems that the intermediate buffer is not yet filled > > > with more data. This results in a gap of one period at the beginning > > > of the playback (it's the second period that doesn't get copied). > > > > Hm, this kind of implementation gets more common nowadays for small > > devices, so we may need a better/simpler framework in furture. > > > > Usually, the filler routine should fill the data as much as possible > > at the time it's called. The size of available data on the > > itermediate buffer can be calculated via PCM appl_ptr. > > > > Possibly, helper functions defined in pcm-indirect.h could be used in > > your case. Check the alsa-devel list archive in the last months, > > threads "Driver design question". The discussions went on there > > regarding a driver implementation without DMA. (The pcm-indirect.h > > routines didn't work for his case well, unforutnately, though...) > > > > > > Takashi > > Thanks for your answer, Takashi! > > when I check the appl_ptr in the trigger callback, it gives me > exactly one period of available data. It means that you set the minimum periods to 1. When it's set to 2, the trigger will be called after two periods are filled (unless the app call snd_pcm_start() explicitly with underfilled stream). (BTW, don't forget Cc to alsa-devel ML.) Takashi ------------------------------------------------------------------------- Take Surveys. Earn Cash. Influence the Future of IT Join SourceForge.net's Techsay panel and you'll get the chance to share your opinions on IT & business topics through brief surveys - and earn cash http://www.techsay.com/default.php?page=join.php&p=sourceforge&CID=DEVDEV _______________________________________________ Alsa-devel mailing list Alsa-devel@xxxxxxxxxxxxxxxxxxxxx https://lists.sourceforge.net/lists/listinfo/alsa-devel
