I would like to use DMA to transfer data using SPI from the M4. I have a process in place where this works, but viewing the output on the scope, the process fails after a period of time (mostly random). Linux is running from the application processor and I thought it may be interfering with the DMA channels used on the M4.
I verified that Linux was interfering with the DMA/SPI transfer by disabling access to DMA for Linux by using the RDC. I viewed the output on a scope and the SPI transfer was complete. When disabling DMA for Linux, Linux crashed, so this isn't a real solution.
What I would like to do is set aside a few channels of the DMA to only be used for the M4. I'm trying to find where in the Linux build that the channel count exists, so that I could limit the end channels to be only used in the M4.