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README: add notes on DMA1

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This commit is contained in:
Zack Buhman 2023-08-24 19:35:47 +00:00
parent 23c0dfa9da
commit 61ca304384
1 changed files with 17 additions and 1 deletions
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16
README.rst
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@ -162,6 +162,22 @@ the increment added an offset of RA0/WA0 after each bus transfer:
Note that the DMA transfer length is always decremented by 1 after 4 bytes are
transferred, regardless of the size of the bus transfer.
Note that selecting DMA1 on a 4-byte bus does not generate misaligned
writes; instead, the following happens:
.. code:: c
uint32_t src[] = { 1, 2, 3, 4, ... };
extern uint32_t dst[];
dst[0] = src[0];
dst[0] = src[1];
dst[1] = src[2];
dst[1] = src[3];
...
// dst = { 1, 1, 3, 3, ... };
The SCU manual (ST-97-R5-072694) contains this contradictory text:
Only add numbers 0 and 1 are valid for the A-Bus and the write unit is