At 2004-07-15 16:48, docydoc wrote:
>Jaap van Ganswijk wrote: > >> At 2004-07-14 19:33, ali marjovi wrote: >> >I'm building a data aquisition system with one 8 bit >> >input sampled at 400khz and need to save stream of >> >about 1 minute duration in PC RAM. >> >I'm using ADC0820 as A2D and also data transfer >> >through ISA bus . >> >My question is about PC part.Is it nessecary to use >> >DMA transfer? >> >> It depends on if you want to do anything else during >> the transport. The strange thing with a PC is that the >> CPU is about as fast as DMA when you use string >> instructions. I'm now talking about early PC's, so >> upto the 286. >> >> With modern CPU's it might even be possible to do it >> with the CPU using interrupts. If you have a 1 Ghz >> CPU (like I have) you can execute about 2 G instructions >> per second so you can execute 2000000/400=5000 >> instructions between two samples, which should be >> enough even when the cache isn't cooperating >> optimally. > >You'll used DMA when you have a controller pushing your A/D-data >directly into the main memory of the host system. >Otherwise you'll have a driver or something similar that work with >the CPU which is not DMA. A driver is software and can work with either interrupts or DMA. Your sentence doesn't seem to make sense. >I can't see any advantage to put just 400k *8 bits /s = 390kB/s with DMA. Please consider that the DMA-devices in the PC are still (for compatibility-reasons) 8-bit wide for the first IC and 16-bit wide for the second IC. (Both 4 channels.) >A CPU is usually fast enough to move the data quick enough to >the computer's main memory if you directly stream it down. Can you redefine 'directly stream it down' in technical terms? >I would not worry about it too much. Don't mess around with DMA >programming at these data rates except you want to buffer in your >application, Of course he wants to buffer it in his application, because it's not a steady stream he is handling. >do some calculation with a DSP for example and then >send it as fast as possible to the host (preferably in burst mode-DMA >then). Huh and now you start advocating a stand-alone board with a DSP? And to top it of, suddenly you think that DMA does make sense? You even confuse me! -- Author: Jaap van Ganswijk INET: [EMAIL PROTECTED] Fat City Hosting, San Diego, California -- http://www.fatcity.com --------------------------------------------------------------------- To REMOVE yourself from this mailing list, send an E-Mail message to: [EMAIL PROTECTED] (note EXACT spelling of 'ListGuru') and in the message BODY, include a line containing: UNSUB CHIPDIR-L (or the name of mailing list you want to be removed from). You may also send the HELP command for other information (like subscribing).
