MySensors/hal/architecture/STM32/README.md

MySensors STM32 Architecture Support

This directory contains the Hardware Abstraction Layer (HAL) implementation for STM32 microcontrollers using the official STM32duino Arduino core.

Overview

The STM32 HAL enables MySensors to run on a wide range of STM32 microcontrollers, including:

• STM32F0 series (Cortex-M0)
• STM32F1 series (Cortex-M3) - Note: This is separate from the old STM32F1 maple implementation
• STM32F4 series (Cortex-M4 with FPU)
• STM32L0/L4 series (Low-power Cortex-M0+/M4)
• STM32G0/G4 series (Cortex-M0+/M4)
• STM32H7 series (Cortex-M7)

Supported Boards

Tested on:

• STM32F401CC Black Pill (84 MHz, 256KB Flash, 64KB RAM)
• STM32F411CE Black Pill (100 MHz, 512KB Flash, 128KB RAM)

Should work on any STM32 board supported by the STM32duino core.

Features

Implemented ✅

• Serial communication (USB CDC and Hardware UART)
• SPI interface for radios (nRF24L01+, RFM69, RFM95)
• EEPROM emulation using Flash memory
• Watchdog support (requires explicit initialization)
• System reboot
• Random number generation (using internal temperature sensor)
• Unique device ID (96-bit STM32 UID)
• CPU voltage reading (via VREFINT)
• CPU temperature reading (via internal sensor)
• CPU frequency reporting
• Critical section (interrupt disable/restore)
• RAM routing table support

Planned 🔄

• Low-power sleep modes (STOP, STANDBY)
• RTC-based timekeeping
• Interrupt-based wake from sleep
• Free memory reporting (heap analysis)

Pin Mapping

STM32F4 Black Pill Example

nRF24L01+ Radio (SPI1)

nRF24     STM32
-----     -----
VCC   --> 3.3V
GND   --> GND
CE    --> PB0  (configurable via MY_RF24_CE_PIN)
CSN   --> PA4  (configurable via MY_RF24_CS_PIN)
SCK   --> PA5  (SPI1_SCK)
MOSI  --> PA7  (SPI1_MOSI)
MISO  --> PA6  (SPI1_MISO)
IRQ   --> PA3  (optional, configurable via MY_RF24_IRQ_PIN)

RFM69/RFM95 Radio (SPI1)

RFM69     STM32
-----     -----
VCC   --> 3.3V
GND   --> GND
NSS   --> PA4  (configurable)
SCK   --> PA5  (SPI1_SCK)
MOSI  --> PA7  (SPI1_MOSI)
MISO  --> PA6  (SPI1_MISO)
DIO0  --> PA3  (IRQ pin, configurable)
RESET --> PA2  (configurable)

Serial Communication

USB CDC:  Serial    (default, MY_SERIALDEVICE)
UART1:    PA9/PA10  (TX/RX)
UART2:    PA2/PA3   (TX/RX)

Optional Status LEDs

On-board LED: PC13 (Blue Pill) or PA5 (Black Pill)
RX LED:       Configurable via MY_DEFAULT_RX_LED_PIN
TX LED:       Configurable via MY_DEFAULT_TX_LED_PIN
ERR LED:      Configurable via MY_DEFAULT_ERR_LED_PIN

PlatformIO Configuration

platformio.ini Example

[env:blackpill_f411ce]
platform = ststm32
framework = arduino
board = blackpill_f411ce

; Upload configuration
upload_protocol = stlink

; Build flags
build_flags =
    -D MY_DEBUG
    -D MY_BAUD_RATE=115200
    -D MY_GATEWAY_SERIAL
    -D MY_RADIO_RF24
    -D MY_RF24_CE_PIN=PB0
    -D MY_RF24_CS_PIN=PA4
    -D MY_RF24_PA_LEVEL=RF24_PA_LOW

; Library dependencies
lib_deps =
    mysensors/MySensors@^2.4.0
    ; Add radio-specific libraries if needed

; Monitor configuration
monitor_speed = 115200

; Debug configuration
debug_tool = stlink

Supported Boards

Common board values for platformio.ini:

• blackpill_f401cc - STM32F401CC Black Pill
• blackpill_f411ce - STM32F411CE Black Pill (recommended)
• bluepill_f103c8 - STM32F103C8 Blue Pill (use old STM32F1 HAL instead)
• nucleo_f401re - STM32F401RE Nucleo
• nucleo_f411re - STM32F411RE Nucleo
• genericSTM32F103C8 - Generic F103C8
• See PlatformIO boards for complete list

Upload Methods

Supported upload_protocol options:

• stlink - ST-Link V2 programmer (recommended)
• dfu - USB DFU bootloader (requires boot0 jumper)
• serial - Serial bootloader (requires FTDI adapter)
• jlink - Segger J-Link
• blackmagic - Black Magic Probe

Arduino IDE Configuration

1. Install STM32duino core:

   • Add board manager URL: https://github.com/stm32duino/BoardManagerFiles/raw/main/package_stmicroelectronics_index.json
   • Tools → Board → Boards Manager → Install "STM32 MCU based boards"

2. Select board:

   • Tools → Board → STM32 boards groups → Generic STM32F4 series
   • Tools → Board part number → BlackPill F411CE

3. Configure USB support:

   • Tools → USB support → CDC (generic 'Serial' supersede U(S)ART)

4. Select upload method:

   • Tools → Upload method → STM32CubeProgrammer (SWD)

Sketch Configuration

Basic Gateway Example

// Enable debug
#define MY_DEBUG

// Gateway mode
#define MY_GATEWAY_SERIAL

// Radio configuration
#define MY_RADIO_RF24
#define MY_RF24_CE_PIN PB0
#define MY_RF24_CS_PIN PA4

#include <MySensors.h>

void setup() {
    // MySensors initializes automatically
}

void presentation() {
    sendSketchInfo("STM32 Gateway", "1.0");
}

void loop() {
    // Add sensor reading code here
}

Basic Sensor Node Example

#define MY_DEBUG
#define MY_RADIO_RF24
#define MY_RF24_CE_PIN PB0
#define MY_RF24_CS_PIN PA4
#define MY_NODE_ID 10

#include <MySensors.h>

#define CHILD_ID_TEMP 0
MyMessage msgTemp(CHILD_ID_TEMP, V_TEMP);

void setup() {
    // Setup code
}

void presentation() {
    sendSketchInfo("STM32 Sensor", "1.0");
    present(CHILD_ID_TEMP, S_TEMP);
}

void loop() {
    float temperature = 22.5; // Read from sensor
    send(msgTemp.set(temperature, 1));
    sleep(60000); // Sleep for 1 minute
}

EEPROM Emulation

The STM32 HAL uses the STM32duino EEPROM library, which provides Flash-based EEPROM emulation:

• Size: Configurable, typically 1-4KB
• Location: Last Flash page(s)
• Wear leveling: Implemented by STM32duino core
• Persistence: Survives power cycles and resets
• Write cycles: ~10,000 writes per page (Flash limitation)

Configuration is automatic. EEPROM size can be adjusted in the STM32duino menu or via build flags.

Low-Power Considerations

Current Status

Sleep modes are NOT YET IMPLEMENTED in this initial release. Calling sleep() functions will return MY_SLEEP_NOT_POSSIBLE.

Future Implementation

The STM32 supports several low-power modes:

• Sleep mode: ~10mA (CPU stopped, peripherals running)
• Stop mode: ~10-100µA (CPU and most peripherals stopped)
• Standby mode: ~1-10µA (only backup domain active)

Implementation will use:

• RTC for timed wake-up
• EXTI for interrupt wake-up
• Backup SRAM for state retention

Troubleshooting

Compilation Errors

Error: Hardware abstraction not defined

• Solution: Ensure you're using STM32duino core, not Arduino STM32 (maple)
• The platform should define ARDUINO_ARCH_STM32

Error: EEPROM.h not found

• Solution: Update STM32duino core to latest version (2.0.0+)

Error: Undefined reference to __disable_irq

• Solution: Ensure CMSIS is included (should be automatic with STM32duino)

Upload Issues

Upload fails with ST-Link

• Check ST-Link connections (SWDIO, SWCLK, GND, 3.3V)
• Verify ST-Link firmware is up to date
• Try: st-flash reset to reset the chip

DFU mode not detected

• Set BOOT0 jumper to 1 (3.3V)
• Press reset button
• Verify with: dfu-util -l
• After upload, set BOOT0 back to 0 (GND)

Runtime Issues

Serial monitor shows garbage

• Check baud rate matches (default 115200)
• USB CDC may require driver on Windows
• Try hardware UART instead

Radio not working

• Verify 3.3V power supply (nRF24 needs clean power)
• Check SPI pin connections
• Add 10µF capacitor across radio VCC/GND
• Verify CE and CS pin definitions

EEPROM not persisting

• EEPROM emulation requires Flash write access
• Check for debug mode preventing Flash writes
• Verify sufficient Flash space for EEPROM pages

Performance Characteristics

STM32F411CE Black Pill

• CPU: 100 MHz ARM Cortex-M4F
• Flash: 512KB
• RAM: 128KB
• Current: ~50mA active, <1µA standby (when implemented)
• MySensors overhead: ~30KB Flash, ~4KB RAM

Benchmarks (preliminary)

• Radio message latency: <10ms (similar to AVR)
• EEPROM read: ~50µs per byte
• EEPROM write: ~5ms per byte (Flash write)
• Temperature reading: ~100µs

Contributing

This STM32 HAL is designed for easy contribution to the main MySensors repository. When contributing:

1. Follow MySensors coding style
2. Test on multiple STM32 variants if possible
3. Document any chip-specific quirks
4. Update this README with new features

References

• STM32duino Core
• STM32duino Wiki
• PlatformIO STM32 Platform
• MySensors Documentation
• STM32 Reference Manuals

License

This code is part of the MySensors project and is licensed under the GNU General Public License v2.0.

Version History

• v1.0.0 (2025-01-17) - Initial STM32 HAL implementation
  • Basic functionality (GPIO, SPI, EEPROM, Serial)
  • Tested on STM32F401/F411 Black Pill
  • Gateway and sensor node support
  • No sleep mode yet (planned for v1.1.0)