1 Disabling I-cache: 2 - Set CONFIG_SYS_ICACHE_OFF 3 4 Disabling D-cache: 5 - Set CONFIG_SYS_DCACHE_OFF 6 7 Enabling I-cache: 8 - Make sure CONFIG_SYS_ICACHE_OFF is not set and call icache_enable(). 9 10 Enabling D-cache: 11 - Make sure CONFIG_SYS_DCACHE_OFF is not set and call dcache_enable(). 12 13 Enabling Caches at System Startup: 14 - Implement enable_caches() for your platform and enable the I-cache and 15 D-cache from this function. This function is called immediately 16 after relocation. 17 18 Guidelines for Working with D-cache: 19 20 Memory to Peripheral DMA: 21 - Flush the buffer after the MPU writes the data and before the DMA is 22 initiated. 23 24 Peripheral to Memory DMA: 25 - Invalidate the buffer before starting the DMA. In case there are any dirty 26 lines from the DMA buffer in the cache, subsequent cache-line replacements 27 may corrupt the buffer in memory while the DMA is still going on. Cache-line 28 replacement can happen if the CPU tries to bring some other memory locations 29 into the cache while the DMA is going on. 30 - Invalidate the buffer after the DMA is complete and before the MPU reads 31 it. This may be needed in addition to the invalidation before the DMA 32 mentioned above, because in some processors memory contents can spontaneously 33 come to the cache due to speculative memory access by the CPU. If this 34 happens with the DMA buffer while DMA is going on we have a coherency problem. 35 36 Buffer Requirements: 37 - Any buffer that is invalidated(that is, typically the peripheral to 38 memory DMA buffer) should be aligned to cache-line boundary both at 39 at the beginning and at the end of the buffer. 40 - If the buffer is not cache-line aligned invalidation will be restricted 41 to the aligned part. That is, one cache-line at the respective boundary 42 may be left out while doing invalidation. 43 - A suitable buffer can be alloced on the stack using the 44 ALLOC_CACHE_ALIGN_BUFFER macro. 45 46 Cleanup Before Linux: 47 - cleanup_before_linux() should flush the D-cache, invalidate I-cache, and 48 disable MMU and caches. 49 - The following sequence is advisable while disabling d-cache: 50 1. dcache_disable() - flushes and disables d-cache 51 2. invalidate_dcache_all() - invalid any entry that came to the cache 52 in the short period after the cache was flushed but before the 53 cache got disabled. 54
