[sdiy] dsPIC33 question..
seb at burnit.co.uk
Thu Nov 13 19:15:01 CET 2008
Eric Brombaugh wrote:
> Someone please correct me if I'm wrong, but I don't believe that SPI
> DMA is particularly useful. The problem is that (at least as I have
> found) the dsPIC SPI port doesn't automatically control the Chip
> Select line in master mode - you need to toggle that bit with firmware
> instructions. That rules out using DMA on the SPI port to handle
> anything except long sequential SPI transfers where the CS line is
> Since typical audio delay applications are going to require multiple
> interleaved read/write RAM accesses, you'll have to manage SPI RAM at
> a per-transaction basis. DMA would work, but setup/teardown overhead
> isn't going to be worth it for two-byte transfers.
Yes, this is right actually. In the 4xD code I am writing 2 bytes, then
reading 2 bytes alternately. So DMA is not going to help. I suppose
one could have the code use buffers and transfer blocks at a time, but
for a delay application where the delay time needs to be changed
dynamically without glitching, that's going to be headache to program.
And hey, I don't mind using an 80 pin package .. all the more room for
CV inputs :)
More information about the Synth-diy