I have written an DMA SPI driver in MQX (but not MQX's driver), however I can't get the DMA to write to externally configured (FlexBus) SRAM. Writes to internal memory works fine. I'm using the K60 processor.
I'm sure there is a protection bit somewhere preventing this, but given the number of peripherals that could effect this (SIM, Flexbus, DMA, Crossbar Swtich, MPU, AIPS), I wanted to put this question to the group in the hopes someone would just know. I have FBSEL set to allow off-chip code and data access. Non-DMA off-chip access works fine.