[GitHub] [incubator-nuttx] hartmannathan commented on pull request #4872: stm32f7:sdmmc defer invalidate until after DMA completion

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hartmannathan commented on pull request #4872:
URL: https://github.com/apache/incubator-nuttx/pull/4872#issuecomment-977993710


   I haven't grokked exactly what the problem is in this particular instance, but one possible issue may occur if buffers are not aligned *and* padded to exact D-Cache line boundaries. From my hazy memory on H7 that's 32 bytes; don't know on F7. I have been bitten by this one in the past:
   
   Why an issue may occur: The "invalidate D-cache" operation basically means "delete the contents of those cache lines." If any other data besides the DMA buffers falls within those cache lines, e.g., variables, newer values of those variables which are in the cache and not yet written to RAM will be lost, leaving older stale values in RAM.
   


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