Hardware Guide
The STM32U5 handles people counting effectively with CMSIS-NN. 786 KB SRAM at 160 MHz provides 4.1x headroom over the 192 KB requirement for 200 KB models. Built-in USB OTG HS enables wireless result reporting.
| Spec | STM32U5 |
|---|---|
| Processor | ARM Cortex-M33 @ 160 MHz |
| SRAM | 786 KB |
| Flash | 2 MB |
| Key Features | Ultra-low-power (best-in-class Cortex-M33), TrustZone hardware security, Hardware crypto (AES/PKA/HASH), SMPS for power efficiency, Up to 2514 KB SRAM on U5A5/U5G9 variants |
| Connectivity | USB OTG HS |
| Price Range | $6 - $15 (chip), $20 - $50 (dev board) |
At 786 KB SRAM, the STM32U5 provides 4.1x the 192 KB minimum for people counting. This generous headroom means the 200 KB model tensor arena, sensor input buffers, and application logic (camera polling, USB OTG HS stack, state management) all fit without contention. The remaining 286 KB after model allocation supports complex application features. The STM32U5 provides 2 MB of flash memory, which accommodates the CMSIS-NN runtime and 200 KB model. Space remains for firmware and basic OTA capability. The STM32U5 combines Cortex-M33 with TrustZone for secure ML inference and ultra-low power consumption. Its 786 KB SRAM is among the largest in low-power MCU families. The SMPS voltage regulator extends battery life in duty-cycled inference scenarios. People Counting requires camera input. The STM32U5 lacks native peripheral support for some of these sensors, requiring external interface circuitry. A camera interface (DVP/DCMI) is not available — SPI-based camera modules may work but with reduced frame rates. Evaluate whether the peripheral gap justifies an alternative MCU with native support. CMSIS-NN provides ARM-optimized neural network kernels that leverage the STM32U5'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 $6-15 per chip ($20-50 for dev boards), the STM32U5 is a reasonable investment for people counting deployments. Key STM32U5 features for this workload: Ultra-low-power (best-in-class Cortex-M33), TrustZone hardware security, Hardware crypto (AES/PKA/HASH), SMPS for power efficiency, Up to 2514 KB SRAM on U5A5/U5G9 variants.
Set up STM32U5 development environment
Install STM32CubeIDE with the latest STM32Cube firmware package. Create a project targeting the STM32U5 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 camera training data
Connect a camera module (e.g., OV2640 via DVP/SPI) to the STM32U5. Write a data logging sketch that captures camera readings at the target sample rate and outputs via serial/SD card. Collect 1000+ labeled samples across all classes. Capture images at the model input resolution (96×96 or lower).
Train model and prepare for CMSIS-NN deployment
Train a quantized MobileNet-SSD or YOLO-Tiny 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 200 KB. Use tflite_micro's CMSIS-NN delegate to automatically route operations to optimized ARM kernels on the STM32U5's cortex-m33 core.
Deploy and validate on STM32U5
Include the CMSIS-NN runtime and compiled model in your STMicroelectronics project. Allocate a tensor arena of 300-500 KB in a static buffer. Run inference on live camera 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.
STMicroelectronics cortex-m7 at 480 MHz with 1024 KB SRAM. $8-20 per chip. Compared to STM32U5: faster clock. Excellent rated.
NXP cortex-m7 at 600 MHz with 1024 KB SRAM. $6-12 per chip. Compared to STM32U5: faster clock. Excellent rated.
STMicroelectronics cortex-m7 at 216 MHz with 512 KB SRAM. $8-15 per chip. Compared to STM32U5: less RAM but lower cost. Good rated.
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