Writing a mini ALSA driver from scratch

[Ludwig Schwardt <schwardt@sun.ac.za>]

Hi,

A student of mine is working on an audio capture driver for an ARM Linux 
system. The ARM (AT91RM9200) processor talks via SSC and I2S to a set of 
audio ADCs that capture 6 channels of 24-bit 192 kHz audio (no playback 
involved).

The application is real-time sound logging (latency not important). I 
figured it might save the application developers some hassles by 
presenting this capture device as a soundcard to Linux. That way it may 
simplify realtime processing by using standard callback interfaces such 
as JACK (less apps to write!).

My questions to the ALSA gurus are:

1) Is this a sound approach? (sorry, that slipped out)

2) Is it possible to write a bare-bones ALSA driver with only capturing 
functionality (no playback/mixer)? What are the bare essentials that 
make up an ALSA driver? (I'm worried about overkill)

3) Are there any existing drivers that could serve as a good template 
for a minimalist driver (I'm ignoring issues such as ISA/PCI etc.), to 
see how viable this option is? I was thinking maybe Gravis Ultrasound or 
such...

4) Is an ALSA driver even possible on ARM (dunno much about mmap and the 
like)?

Thanks in advance for any tips. I was thinking of ploughing back any 
generic stuff along the way (like the AT91 SSC support).

Ludwig Schwardt


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