Can't DMA to off-chip Memory

[pmt]

Hello,

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.

Thanks!

PMT

[soledad]

Hi,

MQX 4.0.2 Kinetis BSPs are prepared for use with DMA. Make sure that you enable DMA for SPI modules in your user configuration. In user config.h, make sure you configure:

  BSPCFG_DSPI0_USE_DMA 1

  BSPCFG_DSPI1_USE_DMA 1

  BSPCFG_DSPI2_USE_DMA 1

build time options. Then build BSP with these configuration. For source code effects, check init_spi.c in the /mqx/source/bsp/

Regards

Sol

[pmt · Accepted solution]

Problem found.  DMA does not interact with cache.  Cache flushes are needed when DMA'ing into cacheable regions.