Merge pull request tock#4166 from tock/core-wg-2024-09-06

doc: wg: core: notes 2024-09-06

doc/wg/core/notes/core-notes-2024-09-06.md

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+# Tock Meeting Notes 2024-09-06
+
+## Attendees
+
+- Branden Ghena
+- Brad Campbell
+- Johnathan Van Why
+- Amit Levy
+- Ben Prevor
+- Tyler Potyondy
+- Pat Pannuto
+- Hudson Ayers
+
+
+## Updates
+
+- Tyler: Doing some research in to low power Tock, specifically using the type
+  system.
+  - Default kernel using 1.2 mA on nRF52. Doing nothing except running UART for
+    process console. Otherwise it is about 200 uA.
+  - Using a $90 power monitor (Power Profiler Kit 2).
+- Amit: Hacking on SMA Q3 smartwatch. (https://shop.espruino.com/banglejs2)
+  - Exposing some issues around buffer management in HILs and screen stack.
+  - Screen is unique with its own special color format.
+  - Question: where to bring up issues with screen?
+    - Brad: Ideally, the tracking issue should be the hub. But any screen
+      changes are fairly difficult, so helpful to know what the goal/intent is
+      before starting a bunch of changes.
+- Hudson: Still working on nightly asm const PR.
+  - Still working on a build.rs/cargo test solution that is suitable.
+  - Difficult to manage the precedence of how options are selected.
+  - Brad: I still think a proper build crate for Tock would make a lot of
+    subtlety much more clear.
+
+
+## Leasable Buffers
+
+- SubSlice in upstream kernel, PacketBuffer in the works.
+- Would be helpful to use SubSlice in SPI HIL.
+- Question: what is the relationship between PacketBuffer and SubSlice?
+  - API: more adjustable slice and unslice with PacketBuffer. Can take/hide
+    arbitrary bytes with PacketBuffer.
+  - PacketBuffer provides guarantees about space at compile time.
+- Question: what is the underlying representation of PacketBuffer?
+  - SubSlice is just a Rust slice and an active range.
+  - PacketBuffer is similar to SubSlice, has slice and active range.
+- How far are we from being able to try out PacketBuffer?
+  - Unclear.
+- How aggressively should we switch to Leasable Buffers?
+  - Brad: Let's do it! https://github.com/tock/tock/issues/3504
+  - Branden: We don't need to wait for PacketBuffer.
+- Hopefully easier to switch SubSlice -> PacketBuffer than [u8] to SubSlice.
+- It can be tricky to switch to SubSlice in a meaningful way. Easy to escape
+  hatch.
+- Fairly easy to switch SPI, but not getting full benefit from SubSlice.
+- Two aspects: enabling new capsules to be able to use SubSlice, and having good
+  reference code to copy from.
+  - Hopefully switching the HIL is the key to allow new capsules to be able to
+    embrace SubSlice.
+- There are three versions: SubSlice, SubSliceMut, SubSliceMutImmut to support
+  different mutability of buffers.
+  - Callbacks make using SubSliceMutImmut hard, need to ensure you get a mutable
+    slice back. Leads to runtime checks.
+
+
+## Updating Rust
+
+- CHERI needs out-of-tree compiler. That version is slightly behind latest Rust.
+- How often do we update Rust?
+- At the point of removing nightly features.
+- We could want stable naked functions.
+- Our current cadence is we update roughly every two months plus when something
+  new is added we want.
+  - Compiler changes might be slowing down, but there are a lot of other tools
+    we use that see more frequent changes.
+- Could use nightlies that correspond to Rust stable versions.
+  - https://forge.rust-lang.org/
+  - Seems like a reasonable option.
+
+
+## Release???
+
+- How close are we to using treadmill for testing for a release?
+  - Basic functionality there (reading console output).
+  - Issues around starting jobs.
+  - Some basic tests are there.
+- Seems like a good time based on the current PRs. More features than fixes or
+  low-level changes.