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Add DMA support to USART API #20

merged 14 commits into from Aug 1, 2019

Add DMA support to USART API #20

merged 14 commits into from Aug 1, 2019


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Also contains some small cleanups of the serial module.

This pull request is based on #19. I recommend reviewing/merging that pull request first.

cc @lthiery

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I just rebased this on the latest master. It still contains all the commits from #16 and #19. Normally I mark pull requests that are based on others as a draft, but I forgot to do so in this case.

I'm working on some changes that require `Transfer::new` to be opened up
to the rest of the crate, so I think it makes sense to not require weird
PAC types when calling it.
The problem with these constructors is that they're not flexible enough.
In general, peripheral APIs might want to present DMA transfers to the
user in a different way than they work in hardware.

For example, the AES peripheral supports only transfers of 32-bit words,
but might want to present an API that works with byte slices (I'm
currently working on this). Another example would be SPI, which might
want to hide two simultaneous DMA transfers (for read and write) behind
a single transfer struct.

This commit doesn't make these use cases possible yet, as some
modifications to the unsafe constructor are still required. But it paves
the way, by exposing that constructor to the peripheral APIs.

Please note that none of this exposes any unsafety to the users. They
will still use the same (safe) peripheral APIs to access DMA.
The new trait, `Buffer`, provides everything the DMA code needs from the
buffer, without requiring implementers to be able to return a slice.
This makes the trait more flexible, as it can be implemented for a
larger variety of types, without requiring any complex transmuting.
The type parameter names were wrong, as they were in a different order
than was used everywhere else in the code. Please note that this didn't
cause any incorrect behavior, as just the names were wrong and nothing
This should be more natural than operating with `u32` words.
This doesn't add DMA support to USART yet, as that still requires
special DMA APIs in the USART module.
@arkorobotics arkorobotics merged commit 8978137 into stm32-rs:master Aug 1, 2019
@hannobraun hannobraun deleted the usart-dma branch August 1, 2019 05:50
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2 participants