With Stimmer's first bit of code I was able to do 1 Million ADC conversions/second, while switching through 8 analog inputs. When I added in some digitalwrites the speed drop was minimal. When I tried to read the data with serial.write() everything came to a screeching halt. I need to be able to write 1.5MB/s and SerialUSB.write() looks like it will work. The latency with the SD cards may slow it down too much, but I do like the idea of writing to a csv or txt file.
stimmer:
SerialUSB works as fast as it can, the baud rate is ignored. Since it's USB2.0 the port is faster than the SAM3X can throw data down it. I've had it running at over 50Mbit/sec.
I like his DMA approach much better because is frees up the processor. While the buffer is being filled I can write the data. but I can't find references on how to use SerialUSB.