Embedded Working Group Meeting 2023-04-04

Attendance

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Announcements
- @adamgreig won't be running meetings for 3 weeks (until 2nd May)
- defmt-brtt (datdenkikniet)
Embedded HAL
- New serial Read/ReadUntilIdle trait, buffered/unbuffered
  - Continued discussion
  - Perhaps it's fine to only have buffered APIs, but should they have some way to see how many bytes are available / should it be possible to use them without blocking until data is available?
  - Proposed closing the unbuffered PR (349), plan for only a buffered API, but not sure if that's embedded-io's Read, or something more uart-specific, or what
- Update SPI to new transactional API
  - Merged!
  - We could consider a closure-based API in the future, but
    for now the slice transactions is the way to go.
svd2rust
- Various recent work on ordering derivedFrom fields to support the Keil/Arm SVD tools https://github.com/rust-embedded/svd/pull/220

Announcements
- e310x svd2rust version update https://github.com/riscv-rust/e310x/pull/28
Embedded HAL
- New i2c merged: https://github.com/rust-embedded/embedded-hal/pull/440
- SPI new transactional API: https://github.com/rust-embedded/embedded-hal/pull/443
  - We discussed this at some length
  - It seems there are still some use cases for the closure-based API that are not met by the slice API
    - Some chips require CS kept asserted while various things happen eg MAX3421
    - Some displays might want to read-modify-writeback a lot of data inside a transaction
    - If the user-provided data needs conversion (eg u16 to u8 with endian swap) this is more efficient inside a closure
  - But, most use cases are probably fine with the slice API (or even the plain write/transfer APIs)
  - And the slice API is very compatible with Linux spidev, while the closure one may need hacking if it can work at all
  - Possibly we start with the slice API and consider adding the closure one alongside later, for drivers that specifically need it
- serial Read, ReadUntilIdle: https://github.com/rust-embedded/embedded-hal/pull/349
  - Discussed the distinction between buffered/unbuffered further.
  - Should read() always return immediately or can it sometimes block?
- embedded-can https://github.com/rust-embedded/embedded-hal/issues/447
Tools
- svd2rust unsafe api discussion ongoing https://github.com/rust-embedded/svd2rust/issues/714#issuecomment-1478278195