buildrob wrote:Ahh ok I see - yeah that's pretty impressive if you can drive it at that SPI speed using DMA transfers as well.
Yeah that's not something you're going to get with an Arduino. At that transfer rate you could pretty much drive them directly from the rPI side (although I imagine you can do some neat tricks with the DMA interface). Do you have any description of your interface between the two boards?
BTW, I'm referring to the PIC32 DMA.
Are you referring to the communication protocol or the hardware interface?
If hardware, it is just a normal SPI interface; 1 clk, 2 data bus and a chip select. The chip select is omitted on the smaller board (PICnc Jr) due to lack of pins. The uart is used for firmware upgrades and a set of i/o is used for handshaking.
There is no formal communication protocol yet as everything is still in a state of flux. The SPI sends and receives data at the same time and the system is configured to transfer 64 bytes at one go (this is the max RPi buffer size). This is done every 1ms. Currently only position commands and position feedback are being transferred. Each command/feedback is 4 bytes long, so there is still a lot of unused space.