On Thu, 20 Mar 2003, Giuliano Pochini wrote:
>
> >> Ok, but how do I build the sg list when bufsize!=sz*periods ? Take
> >> the example above: have I to build 4 periods and let the last one
> >> smaller than 22052 ?
> >
> > it depends on the hardware.
>
> There are no hw constraints IFAIK, but the hw does not provide the
> current dma address. It tells me how many bytes it transferred from
> the trigger-start command, so I need a way to translate that number
> into a frame pointer inside the buffer. To do that I must know
> exactly how long is the buffer to build the sg list and to stranslate
> the byte count in the pointer callback. (it's not enough see below)
> What does alsa expect from .pointer() ? [0-bufsz] or [0-pe*sz] ?
0 ... buffer_size
> > if you need to set up a buffer-descriptor list like via82xx, the above
> > h/w constraint (integer periods) will be most likely necessary.
> > then the buffer size will be aligned to the period size
> > automatically.
>
> It's a quick and simple way to make things work, but it should't
> be necessary.
> The driver currently behaves correctly in two cases:
>
> a - period size is a multiple of PAGE_SIZE
> b - PAGE_SIZE is a multiple of period size
>
> In both cases periods*periodsize matches buffer_size. But if
> periods*periodsize==buffer_size and !a and !b (eg. pe=4, psz=6K,
> bufsz=24K), it doesn't work:
>
> page0 per0[0-4095]
> page1 per0[4096-6143] per1[0-2048]
> page2 per1[2048-6143]
> ...
Note that you'll have to call snd_pcm_period_elapsed() only after the
whole period is elapsed and not fragment of it.
Jaroslav
-----
Jaroslav Kysela <[EMAIL PROTECTED]>
Linux Kernel Sound Maintainer
ALSA Project, SuSE Labs
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