Update ExecuTorch build instructions for Ethos-U65

Author: fidel-makatia

content/learning-paths/embedded-and-microcontrollers/observing-ethos-u-on-nxp/6-build-executorch.md

@@ -8,26 +8,123 @@ weight: 7 # 1 is first, 2 is second, etc.
 layout: "learningpathall"
 ---
 
-For a full tutorial on building ExecuTorch please see learning path [Introduction to TinyML on Arm using PyTorch and ExecuTorch](/learning-paths/embedded-and-microcontrollers/introduction-to-tinyml-on-arm/)
+For a full tutorial on building ExecuTorch please see learning path [Introduction to TinyML on Arm using PyTorch and ExecuTorch](/learning-paths/embedded-and-microcontrollers/introduction-to-tinyml-on-arm/).
 
-1. Build and install the `executorch` pip package from Source:
+## Install ExecuTorch
 
-    ```bash
-    git submodule sync
-    git submodule update --init --recursive
-    ./install_executorch.sh
-    ```
+1. Upgrade pip and install build tools:
 
-# Troubleshooting
+   ```bash
+   pip install --upgrade pip setuptools wheel
+   ```
+
+2. Build and install the `executorch` pip package:
+
+   ```bash
+   ./install_executorch.sh
+   ```
+
+## Build troubleshooting
+
+If the `install_executorch.sh` script fails, manually install the dependencies using the following commands:
+
+```bash
+pip install torch torchvision
+pip install --no-build-isolation .
+pip install --no-build-isolation third-party/ao
+```
+
+## Set up the Arm toolchain
+
+Initialize the Arm-specific environment and accept the EULA:
+
+1. Run the setup script:
+
+   ```bash
+   ./examples/arm/setup.sh --i-agree-to-the-contained-eula
+   ```
+
+2. Source the environment variables:
+
+   ```bash
+   source ./examples/arm/arm-scratch/setup_path.sh
+   ```
+
+## Apply the Ethos-U65 patch
+
+As of this writing, ExecuTorch does not officially support the Ethos-U65. You must patch the `compile_spec.py` file to enable U65 compilation targets within the build system.
+
+1. Create and apply the patch by running the following command block:
+
+   ```bash
+   cat > /tmp/patch_u65.py << 'PATCH'
+   import os
+
+   # Locate the file within the virtual environment
+   filepath = "/root/executorch/.venv/lib/python3.12/site-packages/executorch/backends/arm/ethosu/compile_spec.py"
+
+   with open(filepath, 'r') as f:
+       content = f.read()
+
+   # 1. Inject U65 Configuration Support
+   old_code = '        elif "ethos-u85" in target_lower:'
+   new_code = '''        elif "ethos-u65" in target_lower:
+               self.tosa_spec = TosaSpecification.create_from_string("TOSA-1.0+INT")
+               default_system_config = "Ethos_U65_High_End"
+               default_memory_mode = "Shared_Sram"
+           elif "ethos-u85" in target_lower:'''
+
+   content = content.replace(old_code, new_code)
+
+   # 2. Inject U65 Compile Spec Builder Logic
+   old_check = '''        if "u55" in target_lower:
+               return CompileSpecBuilder(
+                   TosaSpecification.create_from_string("TOSA-0.80+BI+u55")
+               )
+           if "u85" in self.target:'''
+
+   new_check = '''        if "u55" in target_lower:
+               return CompileSpecBuilder(
+                   TosaSpecification.create_from_string("TOSA-0.80+BI+u55")
+               )
+           if "u65" in target_lower:
+               return CompileSpecBuilder(
+                   TosaSpecification.create_from_string("TOSA-1.0+INT")
+               )
+           if "u85" in self.target:'''
+
+   content = content.replace(old_check, new_check)
+
+   with open(filepath, 'w') as f:
+       f.write(content)
+
+   print(f"Patched {filepath}! U65 support added.")
+   PATCH
+
+   python3 /tmp/patch_u65.py
+   ```
+
+2. Verify the patch by running:
+
+   ```bash
+   python3 -c "from executorch.backends.arm.ethosu import EthosUCompileSpec; EthosUCompileSpec(target='ethos-u65-256'); print('U65 OK')"
+   ```
+
+   If successful, you see the output `U65 OK`.
+
+## Additional troubleshooting
 
 1. Allocate at least 4 GB of swap space:
+
    ```bash
    fallocate -l 4G /swapfile
    chmod 600 /swapfile
    mkswap /swapfile
    swapon /swapfile
    ```
-   [optional] Deallocate the swap space after you complete this learning path:
+
+   Deallocate the swap space after you complete this learning path (optional):
+
    ```bash
    swapoff /swapfile
    rm /swapfile
@@ -40,20 +137,23 @@ For a full tutorial on building ExecuTorch please see learning path [Introductio
 
    {{% /notice %}}
 
-2. Kill the `buck2` process:
+2. Kill the `buck2` process if it hangs:
+
    ```bash 
    ps aux | grep buck
    pkill -f buck
    ```
 
 3. Clean the build environment and reinitialize all submodules:
+
    ```bash
    ./install_executorch.sh --clean
    git submodule sync
    git submodule update --init --recursive
    ```
 
-4. Try `install_executorch.sh` again, in development mode:
+4. Try `install_executorch.sh` again:
+
    ```bash
    ./install_executorch.sh
    ```