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- Disabling I-cache:
- - Set CONFIG_SYS_ICACHE_OFF
- Disabling D-cache:
- - Set CONFIG_SYS_DCACHE_OFF
- Enabling I-cache:
- - Make sure CONFIG_SYS_ICACHE_OFF is not set and call icache_enable().
- Enabling D-cache:
- - Make sure CONFIG_SYS_DCACHE_OFF is not set and call dcache_enable().
- Enabling Caches at System Startup:
- - Implement enable_caches() for your platform and enable the I-cache and
- D-cache from this function. This function is called immediately
- after relocation.
- Guidelines for Working with D-cache:
- Memory to Peripheral DMA:
- - Flush the buffer after the MPU writes the data and before the DMA is
- initiated.
- Peripheral to Memory DMA:
- - Invalidate the buffer before starting the DMA. In case there are any dirty
- lines from the DMA buffer in the cache, subsequent cache-line replacements
- may corrupt the buffer in memory while the DMA is still going on. Cache-line
- replacement can happen if the CPU tries to bring some other memory locations
- into the cache while the DMA is going on.
- - Invalidate the buffer after the DMA is complete and before the MPU reads
- it. This may be needed in addition to the invalidation before the DMA
- mentioned above, because in some processors memory contents can spontaneously
- come to the cache due to speculative memory access by the CPU. If this
- happens with the DMA buffer while DMA is going on we have a coherency problem.
- Buffer Requirements:
- - Any buffer that is invalidated(that is, typically the peripheral to
- memory DMA buffer) should be aligned to cache-line boundary both at
- at the beginning and at the end of the buffer.
- - If the buffer is not cache-line aligned invalidation will be restricted
- to the aligned part. That is, one cache-line at the respective boundary
- may be left out while doing invalidation.
- - A suitable buffer can be alloced on the stack using the
- ALLOC_CACHE_ALIGN_BUFFER macro.
- Cleanup Before Linux:
- - cleanup_before_linux() should flush the D-cache, invalidate I-cache, and
- disable MMU and caches.
- - The following sequence is advisable while disabling d-cache:
- 1. dcache_disable() - flushes and disables d-cache
- 2. invalidate_dcache_all() - invalid any entry that came to the cache
- in the short period after the cache was flushed but before the
- cache got disabled.
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