Add Raspberry Pi build instructions to BUILD.md

Documents the rpi and rpi64 platform options for building natively
on 32-bit and 64-bit Raspberry Pi OS respectively.

Author: reissjason

docs/BUILD.md

@@ -0,0 +1,185 @@
+# Building Basic Station
+
+## Prerequisites
+
+### For Native Linux Build
+
+```bash
+sudo apt-get install -y build-essential
+```
+
+### For Yocto/Bitbake Build (MTCDT)
+
+Requires a configured mts-device build environment with Yocto/OpenEmbedded.
+
+## Building Locally (Native Linux)
+
+### Build Variants
+
+| Variant | Description |
+|---------|-------------|
+| `testsim` | Single SX1301 simulator for regression tests |
+| `testms` | Multi-slave SX1301 simulator for regression tests |
+| `testsim1302` | Single SX1302/SX1303 simulator for regression tests |
+| `testms1302` | Multi-slave SX1302/SX1303 simulator for regression tests |
+
+### Build Commands
+
+```bash
+# Build a specific variant
+make platform=linux variant=testsim
+
+# Build output is in build-linux-<variant>/
+ls build-linux-testsim/bin/station
+```
+
+## Building for Raspberry Pi
+
+Basic Station can be built natively on a Raspberry Pi for use with SX1301-based
+concentrators (e.g., RAK2245, IMST iC880A).
+
+### Platform Selection
+
+| Platform | Architecture | Raspberry Pi OS |
+|----------|--------------|-----------------|
+| `rpi` | arm-linux-gnueabihf | 32-bit (armhf) |
+| `rpi64` | aarch64-linux-gnu | 64-bit (arm64) |
+
+To check which architecture your Raspberry Pi is running:
+
+```bash
+gcc -dumpmachine
+# Returns: arm-linux-gnueabihf (32-bit) or aarch64-linux-gnu (64-bit)
+```
+
+### Build Commands
+
+```bash
+# For 64-bit Raspberry Pi OS
+make platform=rpi64 variant=std
+
+# For 32-bit Raspberry Pi OS
+make platform=rpi variant=std
+
+# Build output
+ls build-rpi64-std/bin/station
+```
+
+### Clean Rebuild
+
+If switching platforms or encountering build issues, clean the dependencies:
+
+```bash
+make super-clean
+make platform=rpi64 variant=std
+```
+
+### Running
+
+```bash
+cd examples/live-s2.sm.tc
+~/basicstation/build-rpi64-std/bin/station
+```
+
+Configure your station by editing `station.conf` and providing appropriate
+certificates and server URIs for your LoRaWAN Network Server.
+
+## Building for MTCDT (Yocto/Bitbake)
+
+### Hardware Mappings
+
+| Machine | Card Model | Chipset | Recipe |
+|---------|------------|---------|--------|
+| mtcdt | MTAC-003 | SX1303 | lora-basic-station-sx1303 |
+| mtcdt | MTAC-LORA-1.5 | SX1301 | lora-basic-station |
+| mtcap3 | - | SX1303 | lora-basic-station-sx1303 |
+| mtcap | - | SX1301 | lora-basic-station |
+| mtcap2 | - | SX1301 | lora-basic-station |
+
+### Setup Build Environment
+
+```bash
+cd /path/to/mts-device
+export MACHINE=mtcdt
+source oe-init-build-env build
+```
+
+### Build Recipes
+
+| Recipe | Description |
+|--------|-------------|
+| `lora-basic-station` | SX1301-based concentrators |
+| `lora-basic-station-sx1303` | SX1302/SX1303-based concentrators |
+
+### Build Commands
+
+```bash
+# Build SX1301 variant
+bitbake lora-basic-station
+
+# Build SX1303 variant
+bitbake lora-basic-station-sx1303
+
+# Force recompile after source changes
+bitbake lora-basic-station -c compile -f
+bitbake lora-basic-station
+```
+
+### Output Location
+
+IPK packages are generated in:
+```
+build/tmp/deploy/ipk/mtcdt/lora-basic-station_*.ipk
+build/tmp/deploy/ipk/mtcdt/lora-basic-station-sx1303_*.ipk
+```
+
+### Modifying Source Code
+
+Source code for the recipe is located at:
+```
+build/tmp/work/mtcdt-mlinux-linux-gnueabi/lora-basic-station/<version>/git/
+```
+
+To apply changes:
+1. Copy modified files to the git directory
+2. Run `bitbake <recipe> -c compile -f` to force recompile
+3. Run `bitbake <recipe>` to package
+
+## Running Regression Tests
+
+```bash
+cd regr-tests
+
+# Run all tests
+./run-regression-tests --nohw
+
+# Run with verbose output
+./run-regression-tests --nohw --verbose
+
+# Run specific variant
+./run-regression-tests --nohw --variant=testsim
+```
+
+### Test Timing
+
+| Environment | Duration | Notes |
+|-------------|----------|-------|
+| GitHub CI (parallel) | ~5 minutes | Full suite across all variants |
+| Local (single variant) | ~15-20 minutes | All tests for one variant |
+
+Individual test durations (testms1302 variant):
+
+| Test | Duration | Notes |
+|------|----------|-------|
+| test1-selftests | ~6s | Quick sanity check |
+| test2-pps | ~12s | PPS timing tests |
+| test3-updn-tls | ~80s | TLS handshake overhead |
+| test4-cups | ~46s | CUPS update protocol |
+| test7-respawn | ~7s | Daemon restart |
+
+For a quick smoke test, run `test1-selftests`:
+
+```bash
+cd regr-tests/test1-selftests
+TEST_VARIANT=testms1302 ./test.sh
+```