Oliver Walter
93b4e2c4f8
RTIC 2 firmware for an RP2040 acting as an RS485 slave, reading a Sensirion SHT31 over I2C and answering a custom binary protocol. Split into two crates so the protocol is testable without hardware: - wiredsensor-core: framing, CRC-16/MODBUS, command dispatch and SHT3x data-sheet math. Pure computation, no I/O, no peripherals. Covered by 42 host tests including the CRC-16/MODBUS catalogue vector, the SHT3x data-sheet CRC-8 example, and an exhaustive single-bit-corruption sweep over every byte of a frame. - wiredsensor-fw: the RTIC application, PL011 register driver and SHT31 I2C driver. Requests are answered entirely from a cached reading. An SHT31 high-repeatability conversion takes up to 15 ms, well past the turnaround a master expects, so the sensor is polled at the lowest priority and the bus path never touches I2C. RTIC's priority ceilings make "a conversion cannot delay a reply" a checked property rather than an argument. Two PL011 details drive the low-level approach, since rp2040-hal exposes neither: the receive-timeout interrupt for prompt frame delimiting, and the BUSY flag, which is the only way to know the final stop bit has left the shift register before releasing DE. The HAL performs the fiddly baud-divisor setup once, then the raw peripheral is reclaimed via free(). Note that RTIM cannot be the sole frame delimiter: it only fires while the RX FIFO is non-empty, so a frame landing exactly on the FIFO watermark is drained by the watermark interrupt and never times out. The authoritative delimiter is a monotonic timer measured from the last received byte. Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
7 lines
235 B
TOML
7 lines
235 B
TOML
[toolchain]
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# Pinned so firmware builds are reproducible. RTIC 2 and rp2040-hal 0.12 both
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# work on stable; nothing here needs nightly.
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channel = "stable"
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targets = ["thumbv6m-none-eabi"]
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components = ["rust-src", "clippy", "rustfmt"]
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