[alsa-devel] emu10k1, how to setup DMA for 24bit playback?
c.fertr at gmail.com
Sat Feb 23 14:46:38 CET 2008
Saturday 23 of February 2008 02:05:34 Lee Revell napsal(a):
thanks for your reply.
> I did quite a bit of work on this driver a few years back, among other
> things I implemented the multichannel playback support (the hw:0,3
Yes, I know. This code works well with e-mu cards as well, although it is
limited to 16bit/48kHz. I'd like to improve this as well, but first I have to
finish basic stereo 24bit playback via hw:0,0.
> Do you have a web page with details on your work, or can you explain
> exactly what you've done so far and how it fails? Preferably in patch
Well, if you look at emufx.c around line 1566, you will see how the 24 bit
capture works. The data path (for newer e-mu cards as 1616(M) or 1212M V2) is
physical inputs (24bit) -> FPGA (internal routing) -> emu10k via A3_EMU32IN()
(still 24bit padded to 32bit ) -> DSP code converts 32bit sample to 2 16bit
via snd_emu10k1_audigy_dsp_convert_32_to_2x16() and feeds A_FXBUS2(x) and
A_FXBUS(x+1) with the resulting halfs -> DMA -> PC side joins these two 16bit
halfs into one S32_LE sample and voila, we have 24bit capture.
The driver, however, still lacks 24bit playback, and I'm trying to change
that. I have working DSP routine which converts two 16bit values from
A_FXBUS(x) and A_FXBUS(x+1) into 32bit value for A3_EMU32OUT(), where the
FPGA and physical output are connected.
So all I need is to send 32bit sample divided to two 16bit halfs via two
A_FXBUS() into emu10k DSP. Unfortunatelly, simple changing the sample format
to S32_LE did not the trick :( Any ideas?
> How are you getting your hardware info?
Just from the alsa emu10k source code and some hit and miss experiments.
Unfortunatelly, there are no emu10k datasheets available :(
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