----- Original Message ----- From: "Takashi Iwai" <tiwai@xxxxxxx> To: "YongLi" <sdshliyong@xxxxxxx> Cc: <alsa-devel@xxxxxxxxxxxxxxxxxxxxx> Sent: Thursday, September 28, 2006 8:59 PM Subject: Re: Alsa driver data transfer problem: the MSB is changed to 1 > 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 > Thank you for your email! I am using linux 2.6.16 and did not found the CONFIG_SND_VERBOSE_PROCFS option, it seems that the kernel supports this option automatically. Regarding the /proc/asound/card0/pcm0p/sub0/status file, after I cat something to /dev/dsp, the status file content is: state: RUNNING trigger_time: 1706.262101000 tstamp : 1958.720932000 delay : 16018 avail : 366 avail_max : 3437 ----- hw_ptr : 7872878 appl_ptr : 7888896 I want to know why the OSS-emulation code converts the data automatically, in which source file? If I use mplayer to play some wav or mp3 music, does this convert affect the sound? Thank you again! Tyler Li ------------------------------------------------------------------------- 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
