- From: Christoph Hintermüller <christoph.hintermueller_at_umit.at>
- Date: Tue, 8 Jul 2003 14:38:06 +0200
Hi Josh Am Dienstag, 8. Juli 2003 00:33 schrieb Joshua Jacobs: > We are using the card to read in a long stream of EEG data and would > like to be able to synchronize the data that we are getting from the > card with the timing of images being displayed on the screen. When > using the streaming interface, we find that comedi only gives us blocks > of 4096 bytes of samples at one time. Repeated calls to read from the > card get zero bytes, until 4096 bytes are available, and then all 4096 > bytes are returned by read. How long does it take until the 16 samples per channel (128*16Samples*2Bytes per sample=4096) are converted or read by the card. If it EG: takes a second it doesn't make sens to poll the card for new data until the 16 samples per channel have arrived, which means send the process or thread responsible for reading the data from the card to sleep until one second has passed since the last call to comedi_read or any other method of getting the data. Or in othere words it doesn't make sens to get a block of Data before the block has arrived as a whole :) > > We are using 64 channels and would like to be able to access each 128 > byte chunk as the card reads it in. We have played with comedi's > buffering functions, but had no success. Does anyone have any advice > for us? As said above to me it seems to rather be a matter of timing of the repeated read calls than, a matter of settings for comedi. But I might be completely wrong. yours Christoph -- Dipl.-Ing. Christoph Hintermüller University for Health Informatics and Technology Tyrol Innrain 98, A-6020 Innsbruck, AUSTRIA Tel: +43/ 512/ 58 67 34/ 820; Fax: +43/ 512/ 58 67 34/ 850 Mail: christoph.hintermueller_at_umit.at; Hompage: http://imsb.umit.at
Received on 2003-07-08Z11:38:06