Shared memory access from the A7’s linux user space.

[JSpra]

What is the best mechanism to access shared memory from the A7’s linux user space? I have tried using mmap and was successful at reading shared memory; however, I get memory exceptions when attempting to write. Could it be that I can only write to this memory in kernel space?

I can find documentation for the M4 processor and how to define shared memory in linker script. No luck with linux doc's other than “remoteproc�? and “rpmsg�? documentation, neither give clear instruction on how this is done.

Could you please refer me to some documentation that could help me get a better understanding on how this is done.

Thanks in advance!

[PatrickF]

Hello,

did you find this https://wiki.st.com/stm32mpu/wiki/Exchanging_buffers_with_the_coprocessor ?

and more specifically this example: https://wiki.st.com/stm32mpu/wiki/How_to_exchange_large_data_buffers_with_the_coprocessor_-_example

Regards

[JSpra]

Patrick,

Thanks, this was great help! So is the answer to my question is to use DMA to access memory on the A7's side of the shared memory, ie dma_alloc_writecombine?

I need to get a better understanding of DMA and Cache Coherence, so I guess it's time to do that. I think using rpsmg-sdb-mod is the best approach in the long run: however, I also would like to get an understanding how the shared memory actually works.

Please let me know if I'm on the correct track here,

Thanks for your help!

John