I don't know anything about the DMA, but you should not call calloc() from
within the OS. That does not work in all configurations.Instead include
nuttx/kmalloc,h and call kmm_malloc(). If you want aligned memory, call
kmm_memalgn().Sent from Samsung tablet.
-------- Original message --------From: Adam Feuer <a...@adamfeuer.com> Date:
7/7/20 9:40 PM (GMT-06:00) To: dev@nuttx.apache.org Subject: driver question
about memory and calloc Hi,I am getting the SAMA5D27 SDMMC SD Card driver pull
request ready. There'sone small issue I'm working on, though. There's a place
in the driverinitialization where I calloc() some memory– 466 bytes. DMA data
transferswhile reading from files times out if I don't have the calloc() in
there.With the memory allocated, everything works fine. Nothing writes to
thisblock of memory– I memset it and examined it before, during, and
aftertransfers using GDB. It's just an unused block of memory.I'm trying to
find out if other amounts of memory work– smaller than about100 bytes doesn't
work, and I know it works reliably at 466 bytes. I'lltrack the exact number
down tomorrow.But my question is, why does this work? The driver
datasheets<http://ww1.microchip.com/downloads/en/devicedoc/ds60001476b.pdf>don'tmention
that the chip needs aligned memory for its buffers, and the Atmeland U-Boot
drivers don't use aligned memory. And since nothing isoverwriting the memory,
what is the calloc() doing to prevent the SDMMC DMAengine from completing the
transfer?If anyone has seen behavior like this, I'd love to know it. I'd like
totake this otherwise useless code out, or at least know why I need it.Link to
the specific line of code in
sam_sdmmc.c<https://github.com/starcat-io/incubator-nuttx/blob/feature/sama5d27-sdmmc-support/arch/arm/src/sama5/sam_sdmmc.c#L3737>cheersadam--
Adam Feuer <a...@adamfeuer.com>
