Re: ALSA Driver for ARM

[Takashi Iwai <tiwai@suse.de>]

At Tue, 29 Mar 2005 23:31:08 +0200,
T-Online wrote:
> 
> Hi,
> 
> I have a new hint, but the problem is not solved.
> 
> > I want to programm an driver for the Cirrus CS42516 and the ARM9 CPU 
> > EP93xx also from Cirrus.
> >
> > I think, there are several errors:
> >
> > - when I start aplay, I receive a buffer. A dump to this memory region 
> > show only zeros.
> >
> I have written some characters into the DMA Memory Area (with a Hardware 
> Debugger) when the driver is started, but aplay is not started. After I 
> start aplay, all my characters are overwritten with Zero.
> 
> Which function in ALSA is responsible for filling the DMA Buffer ?

If it's not mmap mode, it must be through
SNDRV_PCM_IOCTL_WRITEI_FRAMES ioctl (note that alsa-lib doesn't use
write syscall).

i.e. snd_pcm_lib_write() -> snd_pcm_lib_writei() ->
  snd_pcm_lib_write_transfer() -> copy_from_user()


Takashi


> > - after the complete buffer is transmitted (but not the complete 
> > file), I receive an underrun from ALSA
> >
> > - I never detect a mmap function call.
> >
> >  
> 
> Thanks,
> 
> Klaus
> 
> 
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