Create COMPILING.md

COMPILING.md

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+# Compiling Pico-FIDO with Custom VID, PID, and AAGUID for RP2350
+
+This guide walks you through compiling the pico-fido firmware from the token2 repository for RP2350 with your custom USB identifiers and AAGUID.
+
+## Prerequisites
+
+Before starting, ensure you have:
+- ARM GCC toolchain installed (for Pico development)
+- CMake 3.13 or higher
+- Pico SDK properly installed
+- Git
+- Make
+
+### Install on Ubuntu 22.04/24.04
+
+```bash
+# Update package lists
+sudo apt-get update
+
+# Install required packages
+sudo apt-get install -y cmake gcc-arm-none-eabi libnewlib-arm-none-eabi build-essential git python3-pip
+
+# Install additional dependencies for Pico SDK
+sudo apt-get install -y libstdc++-arm-none-eabi-newlib
+```
+
+### Download and Setup Pico SDK
+
+```bash
+# Create a directory for Pico development
+mkdir -p ~/pico
+cd ~/pico
+
+# Clone the Pico SDK
+git clone https://github.com/raspberrypi/pico-sdk.git --branch master
+cd pico-sdk
+git submodule update --init
+
+# Verify installation
+cd ~
+echo "Pico SDK path: $HOME/pico/pico-sdk"
+```
+
+**The PICO_SDK_PATH will be:** `$HOME/pico/pico-sdk`
+
+## Step 1: Clone the pico-fido Repository
+
+```bash
+cd ~/pico
+git clone https://github.com/token2/pico-fido
+cd pico-fido
+git submodule update --init --recursive
+```
+
+After this step, your working directory will be: `~/pico/pico-fido`
+
+## Step 2: Modify AAGUID
+
+The AAGUID is defined in `pico-keys-sdk/src/cbor.c`. Open the file and find the line:
+
+```bash
+nano ~/pico/pico-fido/pico-keys-sdk/src/cbor.c
+```
+
+Locate the AAGUID definition (search for `const uint8_t aaguid`):
+
+**Find this:**
+```c
+const uint8_t aaguid[16] = { 0x89, 0xFB, 0x94, 0xB7, 0x06, 0xC9, 0x36, 0x73, 0x9B, 0x7E, 0x30, 0x52, 0x6D, 0x96, 0x81, 0x45 };
+```
+
+**Replace with:**
+```c
+const uint8_t aaguid[16] = { 0xab, 0x32, 0xf0, 0xc6, 0x22, 0x39, 0xaf, 0xbb, 0xc4, 0x70, 0xd2, 0xef, 0x4e, 0x25, 0x4d, 0xb7 };
+```
+
+Save the file (Ctrl+O, Enter, Ctrl+X in nano) or use your preferred editor.
+
+## Step 3: Create Build Directory
+
+```bash
+cd ~/pico/pico-fido
+mkdir build
+cd build
+```
+
+## Step 4: Configure with CMake
+
+Run CMake with your custom VID/PID and board type:
+
+```bash
+ cmake .. -DPICO_SDK_PATH=$HOME/pico/pico-sdk -DPICO_BOARD=pico2 -DUSB_VID=0x349E -DUSB_PID=0x0099
+```
+
+## Step 5: Compile the Firmware
+
+```bash
+make -j$(nproc)
+```
+
+The `-j$(nproc)` flag uses all available CPU cores to speed up compilation.
+
+If compilation succeeds, you'll see:
+```
+[100%] Built target pico_fido
+```
+
+The compiled firmware will be located at:
+```
+build/pico_fido.uf2
+```
+
+## Step 6: Flash to RP2350
+
+1. **Put your RP2350 board into bootloader mode:**
+   - Hold the BOOTSEL button while plugging in USB, or
+   - Hold BOOTSEL and press the RESET button
+
+2. **Find the mount point** - A USB mass storage device will appear:
+   ```bash
+   lsblk
+   # Look for a device like sda1 or sdb1 that appeared recently
+   # Or check: ls /media/$USER/
+   ```
+
+3. **Mount it manually if needed:**
+   ```bash
+   mkdir -p ~/pico/rp2350-mount
+   sudo mount /dev/sdX1 ~/pico/rp2350-mount
+   # Replace sdX1 with the actual device from lsblk
+   ```
+
+4. **Copy the UF2 file:**
+   ```bash
+   cp ~/pico/pico-fido/build/pico_fido.uf2 ~/pico/rp2350-mount/
+   ```
+   
+   Or if the device auto-mounted:
+   ```bash
+   cp ~/pico/pico-fido/build/pico_fido.uf2 /media/$USER/RP2350/
+   ```
+
+5. **Unmount and verify:**
+   ```bash
+   sync
+   sudo umount ~/pico/rp2350-mount
+   # The device will automatically disconnect and reboot
+   ```
+
+The firmware is now installed. The LED should blink periodically after a few seconds.
+
+## Verification
+
+Once flashed:
+1. The LED should blink periodically (idle mode)
+2. When you connect the device, it should appear as a USB HID device with your custom VID/PID (0x349E:0x0099)
+
+Verify with:
+```bash
+lsusb | grep 349E
+# Should show: "Bus XXX Device YYY: ID 349e:0099"
+```
+
+## Troubleshooting
+
+**CMake configuration fails:**
+- Ensure `PICO_SDK_PATH=$HOME/pico/pico-sdk` is set correctly
+- Run `cmake --version` to verify CMake 3.13+
+- If SDK not found, verify it exists: `ls -la $HOME/pico/pico-sdk`
+
+**Compilation fails with cryptography errors:**
+- Ensure submodules are fully initialized: `git submodule update --init --recursive`
+
+**AAGUID not applying:**
+- Check if it's defined as a constant in a header file that was included during compilation
+- Some builds may require a clean rebuild: `rm -rf build && mkdir build && cd build`
+
+**Device doesn't appear after flashing:**
+- Try flashing again, ensure BOOTSEL was held during USB connection
+- Check for any error messages in dmesg: `dmesg | tail -20`
+
+## Notes
+
+- The dummy VID/PID (0xFEFF:0xFCFD) is used by default to avoid licensing issues
+- VID/PID (0x349E:0x0099) can be used only on devices provided by Token2
+- This firmware is released under AGPLv3 - if you distribute modified binaries, you must provide source code
+- The AAGUID identifies your authenticator type in the FIDO ecosystem; however, there is currently no certificate provided, therefore no attestation