add README

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Astro 2019-03-21 17:54:30 +01:00
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# Synopsis
Exposes readings from an ADC pin (currently: *PA3*) of the board via a
TCP service on the Ethernet port.
# Network Protocol
Sensor readings produce lines of `key=value` pairs, joined by `,`,
terminated by `"\r\n"`.
```
t=21000,pa3=685
t=22000,pa3=684
t=23000,pa3=681
t=24000,pa3=696
t=25000,pa3=673
t=26000,pa3=689
t=27000,pa3=657
t=28000,pa3=654
t=29000,pa3=652
t=30000,pa3=662
t=31000,pa3=663
```
| Key | Value | Unit |
|:---:|-------------|------|
| t | Time | ms |
| pa3 | ADC reading | mV |
# LEDs
Colors indicate what the MCU is occupied with.
| Color | Indication |
|:-------:|-------------------|
| Green | WFI (idle) |
| Blue | Network poll |
| Red | Message broadcast |
# Crate features
* `semihosting` enables log output via the **cortex-m-semihosting**
crate. Use only in development! MCU will hang when no OpenOCD is
running.
* `generate-hwaddr` generates an Ethernet MAC address by hashing the
unique device ID from flash memory.
# Instructions
![Made for NixOS](https://nixos.org/logo/nixos-lores.png)
## Build the firmware with `default.nix`
* `nix-build`
* This uses **cargo-vendor** to bundle dependencies, so that unstable versions from git can be used.
* Run `result/bin/flash-adc2tcp` to flash a devboard with OpenOCD and quit.
## Development environment with `shell.nix`
* `nix-shell`
* Spawning `openocd`, the devboard should be connected already.
* Instructions (`cargo run --release`) are printed.