Paul Thanks for your reply and the education. My main reason behind asking this question is that I am using the RME PST card presently to do CPU controlled transfer of data to the memory mapped buffers in those cards. I am interested in using the CPU to do the transfer since I have heard that DMA or busmastering produces many millisecond latency in sound data playback. Such latency would be unacceptable in my app. BTW I am using RTAI to schedule tasks.
I see in the ESS docs that many (maybe all) of their chipsets do something similar to the RME PST card except that the ESS does not use mapped-memory buffers. Instead it appears the use a single FIFO which generates interrupts as the data in the FIFO moves past the half-full (half empty :-) mark). These fifos are much smaller than the RME buffers if I recall correctly. The ESS docs refer to this as "ping-pong" transfer of sound data. I naive have called both the RME and ESS "ping-pong" methods double-buffering. My error. So I guess I should say that I am looking for cards that can use the ping-pong method in addition to the RME and ESS chipsets. Where does the DMA latency arise? Thanks again, Daniel Sheltraw >From: Paul Davis <[EMAIL PROTECTED]> >To: "daniel sheltraw" <[EMAIL PROTECTED]> >CC: [EMAIL PROTECTED], [EMAIL PROTECTED] >Subject: Re: AW: [Alsa-devel] general audio card Q Date: Tue, 30 Jul 2002 >19:25:50 -0400 > > >>i'm not exactly shure, what is double-buffers... the turtle beach > >>pinnacle/fiji has shared memory, that can be accessed > >>simultanously from the pc & the sound card. > > > >Some cards/chipsets (RME PST, ESS solo1) allow one to transfer > >data for playback (record is similar) using a memory-mapped >double-buffer. > >When buffer 1 has emptied its data to the DAC an > >interrupt is issued. An ISR then fills buffer 1 with more > >sound data while the buffer 2 continues to send its data to > >the DAC for playback. When buffer 2 is emptied it causes an > >interrupt and an ISR can fill it again. This goes on and on > >until all data is played back. > >this has nothing to do with DMA or not. what you're describing in ALSA >terms is a configuration with 2 periods per buffer. nothing more >less. just about all ALSA support hardware allows for this >configuration; a few don't allow anything else. > >the question as i read it was about cards that cannot do DMA. no >matter how many periods, buffers or whatever, they rely on the host >CPU to move data into memory on their hardware. such cards are rare, >and getting rarer. see rui's recent post for a description of how >cards that do use DMA use it. > > >In this method the transfer of the data from memory to the > >memory-mapped buffers is performed by the CPU. This is in > >contrast to DMA transfer of data where the busmaster on the > >sound card controls transfer of data from memory to card. > >No, this has nothing to do with "double buffering". "double buffering" >is a description of a particular configuration, not a mechanism. it >can be accomplished in various ways. > > >So far I only know of the two cards mentioned above but there > >must be others that allow data tranfser in this manner. I would > >like to know which cards have the capablity to do this whether > >or not ALSA supports this method yet in their drivers. > >cards that do not use DMA should generally be considered inferior >because of the extra CPU cycles they force on the host system. > >ALSA neither supports nor not-supports this in the drivers. Its an >implementation detail for the low-level (h/w specific) driver code; >the mid-level code knows nothing about it. > >--p > > >------------------------------------------------------- >This sf.net email is sponsored by: Dice - The leading online job board >for high-tech professionals. Search and apply for tech jobs today! >http://seeker.dice.com/seeker.epl?rel_code=31 >_______________________________________________ >Alsa-devel mailing list >[EMAIL PROTECTED] >https://lists.sourceforge.net/lists/listinfo/alsa-devel _________________________________________________________________ Chat with friends online, try MSN Messenger: http://messenger.msn.com ------------------------------------------------------- This sf.net email is sponsored by: Dice - The leading online job board for high-tech professionals. Search and apply for tech jobs today! http://seeker.dice.com/seeker.epl?rel_code=31 _______________________________________________ Alsa-devel mailing list [EMAIL PROTECTED] https://lists.sourceforge.net/lists/listinfo/alsa-devel
