TensorFlow Lite Micro Integration

Overview

Use this skill to bring up TensorFlow Lite for Microcontrollers (TFLM / LiteRT for Microcontrollers) on an MCU: register exactly the ops the model uses, size the tensor_arena correctly, and quantize inputs so Invoke() returns valid output. Most failures are missing ops, an undersized arena, or unquantized input, not model logic. TFLM is Google's official microcontroller runtime and is integrated by several vendor toolchains — Espressif esp-tflite-micro (with ESP-NN kernels), NXP eIQ, and ST X-CUBE-AI, where TFLM is available as an optional runtime alongside ST's own proprietary Cube.AI runtime. Use tinymaix-integration instead when you want a lighter, dependency-free runtime.

When To Use

Use this skill when:

• The user runs tensorflow/tflite-micro and works with tflite::MicroInterpreter, tflite::MicroMutableOpResolver, AllocateTensors(), or Invoke().
• The build or runtime hits Didn't find op for builtin opcode 'CONV_2D', 'QUANTIZE', arena/AllocateTensors failures, or output that is all zeros or drifting.
• The project embeds a .tflite model as a C array (xxd -i) and needs int8 scale/zero_point handling.

Do not use this skill when the model is not yet converted and quantized to .tflite; run the TFLite converter and validate on the host first.

First Questions

Ask for:

• Target core, RAM/flash, and toolchain; whether CMSIS-NN / ESP-NN / vendor kernels are used.
• The .tflite model, its op list (from Netron or flatc), and its input/output dtype (int8, uint8, or float32).
• Current kTensorArenaSize and whether AllocateTensors() returns kTfLiteOk.
• Input scale/zero_point and expected output; a known golden input/output pair.
• Exact symptom: link error, missing-op error, allocation failure, or wrong output.

Integration Checklist

1. Convert and embed the model. Produce a quantized .tflite, then xxd -i model.tflite > model.cc. Reference it via tflite::GetModel(g_model) and check model->version() != TFLITE_SCHEMA_VERSION.

2. Register only the needed ops. Use tflite::MicroMutableOpResolver<N> where N matches the exact count of AddConv2D(), AddDepthwiseConv2D(), AddFullyConnected(), AddReshape(), AddSoftmax(), AddQuantize(), etc. AllOpsResolver (which registers all built-in ops) bloats flash; avoid it in production.

3. Allocate the tensor arena. Declare alignas(16) uint8_t tensor_arena[kTensorArenaSize];, construct tflite::MicroInterpreter with the model, resolver, tensor_arena, and kTensorArenaSize, then use MicroPrintf for logging.

4. Allocate tensors and check the code. Call interpreter.AllocateTensors() and confirm it returns kTfLiteOk. Grow kTensorArenaSize if it fails, then trim toward interpreter.arena_used_bytes().

5. Quantize the input. Read input->params.scale and input->params.zero_point, compute q = round(real / scale) + zero_point, clamp to [-128, 127], and write input->data.int8[i].

6. Invoke and dequantize. Check interpreter.Invoke() == kTfLiteOk, then convert output->data.int8[i] back with real = (q - zero_point) * scale.

Common Failures

• Didn't find op for builtin opcode 'CONV_2D' / 'QUANTIZE': op missing from the resolver, or N in MicroMutableOpResolver<N> too small to hold all Add* calls.
• Opcode version mismatch (same message with version 'N' plus "An older version of this builtin might be supported"): model exported by a newer converter than the runtime; rebuild tflite-micro or re-export.
• AllocateTensors() fails or returns non-kTfLiteOk because kTensorArenaSize is too small.
• Output is all zeros or drifts: input written as raw floats/pixels without applying scale/zero_point.
• Hard fault or stack overflow inside AllocateTensors()/Invoke(): give the calling thread enough stack (typically several KB).
• Unaligned or too-small tensor_arena (missing alignas(16)) causing allocation errors.

Verification

Before claiming TFLM inference works:

• State the model, its op list, input/output dtype, and kTensorArenaSize vs arena_used_bytes().
• Confirm AllocateTensors() and Invoke() both return kTfLiteOk.
• Confirm a golden input reproduces the host reference output within quantization tolerance.
• Confirm input quantization and output dequantization use the tensor's actual scale/zero_point.

Example

User:

TFLM 里 Invoke 报 "Didn't find op for builtin opcode 'DEPTHWISE_CONV_2D'"。

Agent:

1. Asks for the model op list (Netron/flatc) and the current MicroMutableOpResolver<N> registrations.
2. Adds resolver.AddDepthwiseConv2D() and bumps N to match the total Add* count.
3. Re-runs, confirms AllocateTensors() and Invoke() return kTfLiteOk, and checks a golden vector.