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doc: core: add notes from 2024-03-29
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| # Tock Meeting Notes 03/29/2024 | ||
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| ## Attendees | ||
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| - Amit Levy | ||
| - Andrew Imwalle | ||
| - Brad Campbell | ||
| - Leon Schuermann | ||
| - Johnathan Van Why | ||
| - Pat Pannuto | ||
| - Tyler Potyondy | ||
| - Hudson Ayers | ||
| - Alexandru Radovici | ||
| - Alyssa Haroldsen | ||
| - Vishwajith | ||
| - Branden Ghena | ||
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| ## Updates | ||
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| - Amit: Code size analysis. At a completion point. Writing up results now. | ||
| Describing where code size is going, and some recommendations. Initial doc in | ||
| progress. | ||
| - Some results: TBF header parsing not so bad compared to other features. GPIO | ||
| init is tricky. Some small but surprising things. | ||
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| - Tyler: OpenThread: libtock-c PR open. 6LoWPAN bug and alarm are two remaining | ||
| issues. 6LoWPAN bug addressed by trait updates (in progress). | ||
| - 7 minute timer issue. nRF can handle a prescalar. Need more comments on this. | ||
| - PRs to look at: https://github.com/tock/tock/pull/3933, | ||
| https://github.com/tock/tock/pull/3940 | ||
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| - Alex: Packet buffers with [u8]. | ||
| - Leon: Migrating console API down to UART to new interface. Adding room for | ||
| headers and footers in buffers. Useful for protocols. Right now just a byte | ||
| slice interface. | ||
| - Brad: This didn't work for subslice. | ||
| - Leon: Many design iterations, now have a design with is a superset of | ||
| subslice. | ||
| - Alex: Right now use 12 bytes overhead. Once `const` instructions in Rust is | ||
| stable this overhead goes away. | ||
| - Alyssa: Will likely be a while until that is stabilized. I recommend nesting | ||
| in another type with a fixed footer. | ||
| - Leon: Current implementation does not need nightly features. | ||
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| - Hudson: Rebased https://github.com/tock/tock/pull/3934. Need libtock-c driver. | ||
| Interface with debug!() macros? Only works on cortex-m right now. | ||
| - Brad: Is there a riscv equivalent? | ||
| - Hudson, et al.: Unsure. | ||
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| ## Bar for Capsule PRs. | ||
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| - https://github.com/tock/tock/pull/3881 is for userspace support for NMEA | ||
| devices. | ||
| - Issue arising: "is this the right interface?" or "is this interface and its | ||
| capabilities appropriate for upstream Tock". | ||
| - How do we determine if something is suitable for upstream? When do we say no? | ||
| - Brad: I2C some open questions. NMEA: is this suitable? | ||
| - NMEA: unclear | ||
| - Hudson: could this be specific to one chip? | ||
| - We don't know the exact chip. | ||
| - Downside: others would come around and think they could use something, and it | ||
| doesn't quite work right. Some design decisions which weren't great get | ||
| copied. | ||
| - Our bar should (basically has to) be lower for brand-new | ||
| support/drivers/chips. | ||
| - NMEA support is good. | ||
| - Part of the logic is outsourced to userspace. Difficult to reason about the | ||
| driver. | ||
| - NMEA model is like UDP. Have to wait until data is available. Odd fit with | ||
| I2C. | ||
| - What is the process for handling this? Hard to just say "no". Want to avoid | ||
| randomness in the response. | ||
| - Can write down what we want or what the expectations are. Hard to draw the | ||
| line when the metrics are more subjective. | ||
| - Just might not want to include things in upstream. | ||
| - Can we cite previous examples? | ||
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| **ACTION ITEM**: Amit: propose a plan for normative documentation. | ||
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| ## Timer and Prescalar | ||
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| - OpenThread needs a global time clock. On nRF wraps at 512 seconds. | ||
| - https://github.com/tock/tock/issues/3938 to change the prescalar. | ||
| - `time` HIL has overflow functionality. Could notify userspace on overflow and | ||
| keep track of wrap arounds for current time. | ||
| - Not sure even what the right timer to use is. | ||
| - Might be better to use a timer with higher resolution. | ||
| - Can't tie a networking stack to a specific timer. | ||
| - Might not want to wake up every 7 minutes in any case. | ||
| - Could ensure that the counter provided to userspace always wraps at 32 bits. | ||
| - Could shift left 8 bits to make a 24 bit counter look like a 32 bit counter. | ||
| - Brad: what is the simplest approach that really solves this problem? | ||
| - Always have a 32 bit counter. Userspace sets a timer to check more frequently | ||
| than the timer wraps around. | ||
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| ## Libtock-c rewrite | ||
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| - https://github.com/tock/libtock-c/pull/370 | ||
| - 10 left + apps | ||
| - Assign to Amit |