Add README

Author: pennam

README.md

@@ -0,0 +1,42 @@
+# Arduino UNO R4 WiFi USB Bridge firmware
+
+This firmware uses [arduino-esp32](https://github.com/espressif/arduino-esp32/releases/tag/2.0.9)
+
+## Building
+
+```
+./compile.sh
+```
+Running the compile script will:
+
+1. Download the [arduino-esp32 v2.0.9 core](https://github.com/espressif/arduino-esp32/releases/tag/2.0.9) and build tools
+2. Apply needed [patches](core_esp32.patch)
+3. Compile the firmware using arduino-cli
+4. Export binaries in the build directory inside the `UNOR4USBBridge` folder 
+
+The `compile.sh` script will produce a bunch of binary files that can be flashed using [esptool](https://github.com/espressif/esptool/releases) from the build directory:
+
+```
+esptool --chip esp32s3 --port "/dev/ttyACM0" --baud 921600  --before default_reset --after hard_reset write_flash  -z --flash_mode dio --flash_freq 80m --flash_size 4MB 0x0 "UNOR4USBBridge.ino.bootloader.bin" 0x8000 "UNOR4USBBridge.ino.partitions.bin" 0xe000 "../../../boot/boot_app0.bin" 0x10000 "UNOR4USBBridge.ino.bin"
+```
+
+## Packaging
+
+```
+./export.sh
+```
+
+The `export.sh` script will take care of generating a single binary blob including the TLS certificates bundle. Running the export script will:
+
+1. Invoke the `compile.sh` script
+2. Generate the certificate bundle using this [script](certificates/gen_crt_bundle.py) and this [certificates list](certificates/certificates.pem)
+3. Combine everything in a single binary blob that can be flashed from address 0x0 using [espflash](https://github.com/esp-rs/espflash/releases)
+
+```
+espflash write-bin -b 115200 0x0 S3.bin
+```
+
+## Flashing
+
+To flash the firmware the board needs to be in `ESP download` mode. This can be done [manually](unor4wifi-updater#option-2) or using the [unor4wifi-updater](unor4wifi-updater) script.
+