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1Disabling I-cache:
2- Set CONFIG_SYS_ICACHE_OFF
3
4Disabling D-cache:
5- Set CONFIG_SYS_DCACHE_OFF
6
7Enabling I-cache:
8- Make sure CONFIG_SYS_ICACHE_OFF is not set and call icache_enable().
9
10Enabling D-cache:
11- Make sure CONFIG_SYS_DCACHE_OFF is not set and call dcache_enable().
12
13Enabling 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
18Guidelines for Working with D-cache:
19
20Memory to Peripheral DMA:
21- Flush the buffer after the MPU writes the data and before the DMA is
22 initiated.
23
24Peripheral 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
36Buffer 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.
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43- A suitable buffer can be alloced on the stack using the
44 ALLOC_CACHE_ALIGN_BUFFER macro.
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45
46Cleanup 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:
421044b1 50 1. dcache_disable() - flushes and disables d-cache
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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.