At Thu, 28 Sep 2006 16:43:06 +0800, YongLi wrote: > > Hello All, > > I am desiging a TI sound card driver on my ARM board using Linux 2.6.18. > > The ARM SOC uses IIS and IIC to control this soud codec chip. > > I found a stranger problem reltaed to the sound PCM data: The data transfered by DMA is different from the data I write to the sound device! > > If I perform this command: > > cat test.txt > /dev/dsp > > using the printk to trace the data flow, I found the snd_pcm_oss_write function write all the data in test.txt to > substream->runtime->oss.buffer. However, In the snd_pcm_plug_write_transfer function, the channel changes and the data is different: > > original data(text.txt): > [00]=30 > [01]=31 > [02]=32 > [03]=33 > [04]=34 > [05]=35 > [06]=36 > [07]=37 > [08]=38 > [09]=39 > [10]=0a > > The modified data: > [00]=00 > [01]=b0 > [02]=00 > [03]=b0 > [04]=00 > [05]=b1 > [06]=00 > [07]=b1 > [08]=00 > [09]=b2 > [10]=00 > [11]=b2 > [12]=00 > [13]=b3 > [14]=00 > [15]=b3 > > It seems that all the 8th bit are changed to 1. I am not sure if it is correct. The OSS-emulation code converts format, rate, channels, etc, automatically for the parameters that hardware accepts. So, "cat /dev/dsp" doesn't always pass the raw data as it is. Check the PCM status on /proc/asound/card0/pcm0p/sub0/* (enabled when built with CONFIG_SND_VERBOSE_PROCFS). Takashi ------------------------------------------------------------------------- Take Surveys. Earn Cash. Influence the Future of IT Join SourceForge.net's Techsay panel and you'll get the chance to share your opinions on IT & business topics through brief surveys -- and earn cash http://www.techsay.com/default.php?page=join.php&p=sourceforge&CID=DEVDEV _______________________________________________ Alsa-devel mailing list Alsa-devel@xxxxxxxxxxxxxxxxxxxxx https://lists.sourceforge.net/lists/listinfo/alsa-devel
