bare-metal MCUs No BufferDataLoader ?

[Faboulou]

Hello !

Problem Description

I’m currently working on deploying ExecuTorch on a bare-metal microcontroller featuring an Arm Cortex-M + Ethos-U55 NPU.

The .pte model is stored in external QSPI flash and must be executed XIP.

However, when configuring the CMake build for bare-metal, the system disables all data loader extensions:

-DEXECUTORCH_BUILD_ARM_BAREMETAL=ON
-DEXECUTORCH_BUILD_EXTENSION_DATA_LOADER=OFF # (forced by compatibility)

In the current ExecuTorch examples and documentation — particularly in
backends/cadence/executor_runner.cpp
— the BufferDataLoader is the only documented method to load a .pte.

Unfortunately, this class resides in the extensions module and cannot be used in a bare-metal build. That leaves some uncertainty about how to properly load a model directly from external flash (XIP) when extensions are disabled.

I’m hoping to clarify a few key points and open discussion around the official or recommended path for this scenario.

Questions

• What is the intended mechanism to load the model when using bare-metal + XIP?
• For the Ethos-U55 backend, is there a required initialization step for the delegate in bare-metal environments?

Thanks in advance

[asimhusain-ai]

#include "executor.hpp"

// Linker symbols for .pte in QSPI flash
extern const uint8_t exec_model_start[];
extern const size_t exec_model_size;

// Tensor arena in SRAM
uint8_t tensor_arena[256 * 1024]; // adjust size

int main() {
exec::Options opts;
opts.use_ethos_u55 = true;
opts.tensor_arena = tensor_arena;
opts.tensor_arena_size = sizeof(tensor_arena);

exec::Program program(opts);

// Load model directly from XIP flash
program.load(exec_model_start, exec_model_size);

// Run model
program.run();

return 0;

}

[Faboulou]

Hi @asimhusain-ai !

Thank you for sharing your example.

I believe there might be a few API differences compared to the current ExecuTorch runtime:

• The Program::load() method actually expects a DataLoader* (for example BufferDataLoader), not raw pointers to model data.

• There’s no Options struct in the current ExecuTorch

• the Program class doesn’t have a run() method

• when cross-compiling for ARM targets, program.h isn’t available — only a reduced runtime API is built for embedded use.

So your snippet may compile against an experimental branch, but not against the current mainline ExecuTorch :/

Thanks again for sharing it