On Sat, 4 Oct 2003, Winfried Ritsch wrote:
>
> Hello !
>
> (A question from an newbie-developer to make it perfect ;-)
>
> I am writing an ALSA-lowleveldriver for the RME HDSP-MADI card.
> (which have 64Audion in and out and an 128in64(= 8192Fader) Mixer
> see http://www.rme-audio.de/hdsp/hdspmadi.htm ) Coding is quite
> complete but I have trouble with the memory management.
>
> The Card uses ScatterGather Buffer, each channel 64kB and this
> has to be asigned (to be safe) before activation, so I want
> to allocate SGbuffer (64+64)*64*1024=8388608 in 4k-blocks.
>
> I do a
>
> snd_pcm_lib_preallocate_pci_pages_for_all(hdspm->pci, pcm,8388608l,8388608l)
>
> after making the pcm_device.
>
> Here the questions:
>
> 1) How can I get the sgbuf pointer ?
>
> ... since in the streams runtime is not set and therefore (besides the
> Documentation says is (snd_pcm_sgbuf_t*)substream->dma_private which I
> couldnt find)
>
> sgbuf = (snd_pcm_sgbuf_t*)substream->runtime->dma_private;
>
> is not assigned.
>
> but when I activate the card (for MIDI for example) there must be
> memory asigned und I think doing it in hw_params is to late.
Note that ALSA has SG routines only for PCM streams and it's lifetime is
limited only for stream lifetime. If hardware needs to allocate a big
buffer at the initialization phase, you have to do it yourself.
> 2) If it is bound to substream is always the same substream the
> capture or playback or are the assigned dynamically on calling ?
It depends on hardware parameters and on application. If your hardware
supports multiple equal streams using same i/o connector (hardware
mixing), then the substream might be allocated dynamically, but
application might still request the exact substream number.
If your hardware uses only a few totaly independent streams, create PCM
devices with one substream.
Jaroslav
-----
Jaroslav Kysela <[EMAIL PROTECTED]>
Linux Kernel Sound Maintainer
ALSA Project, SuSE Labs
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