STM32F767 Thermal Prediction Demo

Real-time thermal prediction using a linear regression model on STM32F767ZI, demonstrating TCM (Tightly Coupled Memory) performance optimization.

Overview

This project implements a simple thermal management system that predicts internal component temperature based on:

• Ambient temperature (°C)
• Heat sink temperature (°C)
• Drive current (A)

The system uses a pre-trained linear regression model and provides cycle-accurate performance measurements via UART output.

Hardware Requirements

• MCU: STM32F767ZI (Cortex-M7, 216 MHz)
• Board: STM32 Nucleo-144 or compatible
• Peripherals:
  • USART3 for debug output (115200 baud)
  • HSE crystal/oscillator (8 MHz)

Key Features

Performance Optimization

• TCM Memory: Code and data placed in zero-wait-state memory
  • ITCM (16 KB): Fast instruction execution
  • DTCM (64 KB): Fast data access
• MPU Configuration: Non-cacheable AXI SRAM region for DMA operations
• Cycle Counter: DWT-based performance measurement

Build Configurations

• Standard build: Code runs from Flash with normal SRAM
• Fast RAM build (USE_FAST_RAM): Critical code/data in TCM for maximum performance

Project Structure

firmware/
└── app/
    ├── include/
    │   ├── mem_place.h         # Memory placement macros (FAST_CODE, FAST_DATA)
    │   ├── project_init.h      # Hardware initialization (TCM, MPU, DWT)
    │   ├── regression_model.h  # Linear model interface
    │   └── thermal_demo.h      # Demo application API
    └── src/
        ├── regression_model.cpp # Model implementation
        └── thermal_demo.cpp     # Demo logic and UART output

Application/
└── User/
    └── Core/
        └── main.cpp             # Application entry point

Building

STM32CubeIDE

1. Open the project in STM32CubeIDE
2. Generate BSP
3. Build the project (Ctrl+B)

Build Flags

For TCM optimization, define USE_FAST_RAM:

-DUSE_FAST_RAM

Memory Map

Based on STM32F767ZI architecture and linker script:

ITCM (16 KB):
  0x00000000 - 0x00003FFF    .fast_code section (instruction TCM)

DTCM (64 KB):
  0x20000000 - 0x2000FFFF    .fast_data, .fast_bss sections (data TCM)

SRAM1 (368 KB):
  0x20010000 - 0x2006BFFF    Main RAM (.data, .bss, heap, stack)

SRAM2 (16 KB):
  0x2006C000 - 0x2006FFFF    Additional SRAM

Flash (2 MB):
  0x08000000 - 0x081FFFFF    Program code and constants

Usage

Basic Operation

1. Flash the firmware to the STM32F767
2. Connect a serial terminal to USART3 (115200 baud, 8N1)
3. Observe real-time predictions with timing information:

[Thermal Regression] init
Tamb=24.1C Tsink=23.0C I=0.58A -> T_int_hat=26.45C | 152 cyc (~0.704 us)
Tamb=24.2C Tsink=23.1C I=0.62A -> T_int_hat=26.78C | 148 cyc (~0.685 us)
...

API Functions

// Initialize with UART handle
ThermalDemo_Init(&huart3);

// Enable simulated inputs (default: enabled)
ThermalDemo_EnableSimulatedInputs(true);

// Or provide real sensor values
ThermalDemo_SetInputs(25.0f, 24.0f, 0.65f);

// Run one inference cycle
ThermalDemo_Step();

// Get last prediction without printing
float temp = ThermalDemo_GetLastPredictionC();

Performance Comparison

Typical inference timing (216 MHz, -O0):

Configuration	Cycles	Time (μs)
Flash/SRAM	~308	~1.43
TCM (FAST_RAM)	~274	~1.27

Performance gain: ~11% faster with TCM

Model Details

The linear regression model was trained offline (see Temperature Model Training.ipynb) with the following coefficients:

// Model: T_internal = w0*T_amb + w1*T_sink + w2*I_drive + bias
w = [0.594197, 0.308914, 4.995486]
b = 1.945341

Initialization Sequence

Critical initialization order in main():

1. MPU_SetAXI_NoCache()    // Configure non-cacheable region
2. EnableTCM()              // Enable ITCM/DTCM
3. CopyTCM()                // Copy code/data to TCM
4. HAL_Init()               // HAL initialization (can now use FAST_CODE/DATA)
5. SystemClock_Config()     // Configure 216 MHz clock
6. Peripheral init          // GPIO, UART, etc.
7. DWT_ForceEnable()        // Enable cycle counter

Important: TCM must be initialized before HAL_Init() to ensure any HAL code/data marked with FAST_CODE/FAST_DATA is properly placed.

Linker Script Requirements

The linker script must define the following sections for TCM operation:

/* ITCM section for fast code */
.fast_code : {
    _sitcm = .;
    *(.fast_code)
    _eitcm = .;
} >ITCM AT>FLASH

/* DTCM section for fast data */
.fast_data : {
    _sdtcm = .;
    *(.fast_data)
    _edtcm = .;
} >DTCM AT>FLASH

/* DTCM BSS section */
.fast_bss (NOLOAD) : {
    _sdtcmbss = .;
    *(.fast_bss)
    _edtcmbss = .;
} >DTCM