rp2/rp2_dma: Reduce footprint of the DMA control fields table.#19014
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agatti wants to merge 1 commit intomicropython:masterfrom
Open
rp2/rp2_dma: Reduce footprint of the DMA control fields table.#19014agatti wants to merge 1 commit intomicropython:masterfrom
agatti wants to merge 1 commit intomicropython:masterfrom
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This commit shortens the amount of space taken by the DMA control fields table, and explicitly marks it as `const`. The DMA fields info table used a full-size QSTR index value, and 9 bits of numeric information. Given that the QSTR index could be converted into a `qstr_short_t`, there is no fields spill outside a machine word boundary - albeit with having 7 unused bits but there isn't much that can be done for that. The effective structure size for each entry is halved, from 8 bytes down to 4. Also, the structure is only read from, yet it was not marked as `const`. Marking the structure as constant did not help reduce the final size but at least correctly signals the compiler that no write accesses are possible. This shrinks the RPI_PICO/RPI_PICO_W build by 56 bytes, with a similar size reduction for RPI_PICO2/RPI_PICO2_W. Signed-off-by: Alessandro Gatti <[email protected]>
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Summary
This PR shortens the amount of space taken by the DMA control fields table, and explicitly marks it as
const.The DMA fields info table used a full-size QSTR index value, and 9 bits of numeric information. Given that the QSTR index could be converted into a
qstr_short_t, there is no fields spill outside a machine word boundary - albeit with having 7 unused bits but there isn't much that can be done for that. The effective structure size for each entry is halved, from 8 bytes down to 4.Also, the structure is only read from, yet it was not marked as
const. Marking the structure as constant did not help reduce the final size but at least correctly signals the compiler that no write accesses are possible.This shrinks the RPI_PICO/RPI_PICO_W build by 56 bytes, with a similar size reduction for RPI_PICO2/RPI_PICO2_W.
Testing
The
tests/ports/rp2/rp2_dma.pytest was executed successfully on a RP2040.Generative AI
I did not use generative AI tools when creating this PR.