topic Can't DMA to off-chip Memory in MQX Software Solutions

Can't DMA to off-chip Memory

pmt — Sat, 15 Feb 2014 15:52:48 GMT

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

Re: Can't DMA to off-chip Memory

soledad — Fri, 21 Feb 2014 21:27:25 GMT

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

Re: Can't DMA to off-chip Memory

pmt — Thu, 01 May 2014 16:47:49 GMT

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