Async Serial Transmission using the Video Hardware

Brian Fairchild

Has anyone done much work on using the video hardware for async serial comms? Nothing obvious showed up with a forum search.

I've put together a proof-of-concept in PASM using the video shifter to output a long to a single pin a bit at a time, giving the possibility of 3 bytes per WAITVID. It strikes me as a very efficient way to handle async tx but I can't believe I'm the first one to try this.

Using WAITVID means that program execution will stall which makes full duplex in a single COG interesting although as long as you can engineer arriving at the WAITVID just before it will be executed then you can minimise any latency.

kuroneko

Brian Fairchild said...
I've put together a proof-of-concept in PASM using the video shifter to output a long to a single pin a bit at a time, giving the possibility of 3 bytes per WAITVID.

Do you have a receiver as well? What's the max raw bit rate you can handle?

Post Edited (kuroneko) : 4/13/2009 8:49:05 AM GMT

Brian Fairchild

No receiver - I can't see any way of using the video hardware for that as there's no obvious way to get data from the outside world into the video shift register. As a transmitter the hardware will support whatever the maximum video rate is so I guess up to 128Mbps.