[GitHub] [incubator-nuttx] xiaoxiang781216 edited a comment on pull request #4878: cache_invalidate: fix unalign cacheline invalidate & add cache coherence config for semihosting option

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xiaoxiang781216 edited a comment on pull request #4878:
URL: https://github.com/apache/incubator-nuttx/pull/4878#issuecomment-979227329


   @hartmannathan make a clear explanation here https://github.com/apache/incubator-nuttx/pull/4872:
   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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