Hardware Guide
For fall detection, the STM32H7 with CMSIS-NN scores Excellent. Its 1024 KB internal SRAM (16.0x the required 64 KB) and 480 MHz clock ensure smooth real-time inference on 20 KB models. Hardware DSP extensions boost throughput.
| Spec | STM32H7 |
|---|---|
| Processor | ARM Cortex-M7 @ 480 MHz |
| SRAM | 1024 KB |
| Flash | 2 MB |
| Key Features | Double-precision FPU, L1 cache (16 KB I + 16 KB D), JPEG codec, Chrom-ART Accelerator (DMA2D) |
| Connectivity | Ethernet, USB OTG HS/FS |
| Price Range | $8 - $20 (chip), $30 - $80 (dev board) |
The STM32H7's 1024 KB SRAM provides 16.0x the 64 KB minimum for fall detection. This generous headroom means the 20 KB model tensor arena, sensor input buffers, and application logic (imu polling, Ethernet stack, state management) all fit without contention. The remaining 974 KB after model allocation supports complex application features. Flash storage at 2 MB comfortably houses the CMSIS-NN runtime, the 20 KB model binary, application firmware, and OTA update partitions for field upgrades. Flash usage is well within budget for this configuration. The STM32H7 at 480 MHz with double-precision FPU and ART accelerator is among the highest-performance Cortex-M MCUs in ST's lineup. Its 1 MB SRAM accommodates models that smaller MCUs cannot fit in memory. Dual-bank flash enables safe OTA firmware updates during operation. For fall detection, connect an IMU sensor (e.g., MPU6050 or LSM6DS3 via I2C/SPI) via SPI to the STM32H7. Sample at 50-200 Hz and collect windows of 64-256 samples as model input. The DSP extensions efficiently compute FFT features from raw sensor data. CMSIS-NN provides ARM-optimized neural network kernels that leverage the STM32H7's DSP instructions and floating-point unit for maximum inference throughput on Cortex-M. The kernels are hand-optimized in assembly for critical operations (Conv2D, DepthwiseConv2D, FullyConnected). Combine with TFLite Micro's CMSIS-NN delegate for the best performance on ARM targets. At $8-20 per chip ($30-80 for dev boards), the STM32H7 offers strong value for fall detection deployments. 22 PlatformIO-listed boards provide decent hardware selection. Key STM32H7 features for this workload: Double-precision FPU, L1 cache (16 KB I + 16 KB D), JPEG codec, Chrom-ART Accelerator (DMA2D).
Set up STM32H7 development environment
Install STM32CubeIDE with the latest STM32Cube firmware package. Create a project targeting the STM32H7 and verify basic functionality (blink LED, serial output). For CMSIS-NN, clone the framework repository and add it as a library dependency. Ensure the toolchain supports C++11 or later for the ML runtime.
Collect imu training data
Connect an IMU sensor (e.g., MPU6050 or LSM6DS3 via I2C/SPI) to the STM32H7 via I2C. Write a data logging sketch that captures imu readings at the target sample rate and outputs via serial/SD card. Collect 500+ labeled samples across all classes. Include normal operating conditions and edge cases in your dataset.
Train model and prepare for CMSIS-NN deployment
Train a LSTM or 1D-CNN on IMU time-series in TensorFlow/Keras. Apply int8 post-training quantization via the TFLite converter — this is essential for CMSIS-NN's optimized kernels. The quantized model should be under 20 KB. Use tflite_micro's CMSIS-NN delegate to automatically route operations to optimized ARM kernels on the STM32H7's cortex-m7 core.
Deploy and validate on STM32H7
Include the CMSIS-NN runtime and compiled model in your STMicroelectronics project. Allocate a tensor arena of 30-50 KB in a static buffer. Run inference on live imu data and compare predictions against your test set. Log results to serial for desktop validation. Measure inference latency and peak RAM usage to verify they meet application requirements.
NXP cortex-m7 at 600 MHz with 1024 KB SRAM. $6-12 per chip. Compared to STM32H7: cheaper. Excellent rated.
Renesas cortex-m33 at 200 MHz with 512 KB SRAM. $6-12 per chip. Compared to STM32H7: less RAM but lower cost, cheaper. Excellent rated.
STMicroelectronics cortex-m7 at 216 MHz with 512 KB SRAM. $8-15 per chip. Compared to STM32H7: less RAM but lower cost. Excellent rated.
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