CF Speed with AVR DOS

rredding · Joined: 25 Mar 2005 Posts: 63 Location: Tacoma WA

I have a project where I need to send a continuous stream of 16 bit values to 8 DACs at a rate of 48000 Hz. I plan on using an ATMEGA 128 running at 16MHZ and the DAC is an SPI device. I will need to loop through a large number of values where each DAC will have an independent set of values. Essentially it is to be an 8 channel, synchronized arbitrary waveform generator. The blocks of values may be several megabytes in size for each DAC. I may loop through one set of values in a block N times, then switch to another block for N times, etc. In my application, the processor can be devoted to the data streaming funciton completely. I am considering BASCOM-AVR and AVR-DOS.

So, I suppose my necessary data rate from the CF is roughly 800K Bytes per soecond. Is there someone out there that has used AVR-DOS where data streaming like this is performed? Do I need to set up some sort of buffer to avoid glitches in the data stream? Any other issues I need to bear in mind?

Thank you

philm · Joined: 14 Jul 2004 Posts: 138 Location: Australia

rredding,
I don't think a data rate of 800kB/s is achievable.
Using a 16MHz clock gives you 20 clock cycles per byte. To get a single byte from the file system buffer (or a secondary buffer) to your SPI DAC will take up almost all the 20 clock cycles, and there is no time left to fill the buffer from any source.
Phil

bzijlstra · Posted: Tue May 10, 2005 4:12 pm Post subject: Throughput Compact Flash....

Have done some tests. On a ATA Harddrive controller from www.edtp.com (ATmega128) and a Compact Flash card I got a throughput of 570 kb/sec.

There are some low level routines for writing Harddisk and Compact Flash on my homepage.

Bye
Ben Zijlstra

rredding · Joined: 25 Mar 2005 Posts: 63 Location: Tacoma WA

Well, seeing as I only truely need 6 of the 8 available channels of the octal DAC for my app and that I could probably cut back my rate to about half, if I need too, it might all work out. That gives me about 55 cycles per byte and a rate of 288 KB/s which should be workable, if I use low level code. Thank you both for your feedback!