Cortex-M33 Core Firmware

The firmware deployed on the Arm Cortex-M33 core includes support for the Arm Ethos-U software stack v24.08, which contains software components (e.g. Arm Ethos-U driver, TensorFlow Lite Micro, Arm CMSIS-NN and RPMsg). It passively listens for communication from Linux and responds to Ethos-U NPU related requests, including communication checks (e.g. ping), capability queries and inference execution.

When an inference request arrives from Linux (Cortex-A55 core) over RPMsg:

1. The firmware reads the model and input data from a shared memory region set up by Linux.
2. Creates and initializes the TensorFlow Lite Micro interpreter.
3. Triggers inference execution.
   1. The Ethos-U custom operators (ethos-u) are offloaded to the Ethos-U55 NPU.
   2. Other operators that were not offloading during compilation are executed on the Cortex-M33 core using CMSIS-NN or TFLite Micro reference kernels depending on operator support.
4. Once inference has completed, the firmware will write the results to shared memory and notifies Linux over RPMsg.

Note

The firmware is already included in the rootfs as part of the Linux source package.

An update to the firmware file is only required when enabling logging or modifying the source code.