full duplex problem

Andriy Gapon agapon at cv-nj.com
Fri Oct 17 09:50:40 PDT 2003

Maybe I misunderstand how full duplex is supposed to work, but I observe the 
following problem - when one application writes to /dev/dsp and then I start 
reading from the device with another application the playback becomes much 
slower, it's hard to say how much exactly, but definetly slower than 
half-speed. Another strange thing is that if I start the recording application 
first (it reads from the device in blocking mode) and then I start the 
playback application, the recording application would get EAGAIN (Resource 
temporarily unavailable) error, which is very surprising. A recording 
application can be as simple as `cat` in this case.

My system/hardware/config:


sbc0: <Creative SB AWE64 Gold> at port 0x220-0x22f,0x330-0x331,0x388-0x38b irq 
5 drq 1,5 on isa0
sbc0: setting card to irq 5, drq 1, 5
pcm0: <SB16 DSP 4.16> on sbc0

FreeBSD Audio Driver (newpcm)
Installed devices:
pcm0: <SB16 DSP 4.16> at io 0x220 irq 5 drq 1:5 bufsz 4096d (1p/1r/6v channels 

hw.snd.targetirqrate: 32
hw.snd.report_soft_formats: 1
hw.snd.verbose: 1
hw.snd.maxautovchans: 0
hw.snd.pcm0.buffersize: 4096
hw.snd.pcm0.vchans: 6

I can not find any reports of problems with full duplex with SB hardware and 
FreeBSD since after circa 97, so I am a little bit puzzled. I will apprecite 
any ideas at what I might try to do or what I should read.

Andriy Gapon

More information about the freebsd-multimedia mailing list