Electronics

This is a minimal example of using timer interrupts on PlatformIO / Arduino using HardwareTimer (which is a part of the PlatformIO STM32 Arduino installation – no need to install a library). Tested on the Olimex E407 board. It will run on almost any STM32 processor but you might need to adjust PC13 to the PIN connected to the LED. The example will blink the LED once per second.

#include <Arduino.h>

HardwareTimer timer(TIM1);
bool ledOn = false;

void OnTimer1Interrupt() {
    ledOn = !ledOn;
    digitalWrite(PC13, ledOn ? HIGH : LOW);
}

void setup() {
    pinMode(PC13, OUTPUT);
    // Configure timer
    timer.setPrescaleFactor(2564); // Set prescaler to 2564 => timer frequency = 168MHz/2564 = 65522 Hz (from prediv'd by 1 clocksource of 168 MHz)
    timer.setOverflow(32761); // Set overflow to 32761 => timer frequency = 65522 Hz / 32761 = 2 Hz
    timer.attachInterrupt(OnTimer1Interrupt);
    timer.refresh(); // Make register changes take effect
    timer.resume(); // Start
}

void loop() {
}

Problem:

When you click on Start debugging, press F5 or click on the debug start triangle in PlatformIO

the firmware builds but then nothing happens:

Linking .pio/build/olimex_e407/firmware.elf
Checking size .pio/build/olimex_e407/firmware.elf
Advanced Memory Usage is available via "PlatformIO Home > Project Inspect"
RAM:   [          ]   0.7% (used 936 bytes from 131072 bytes)
Flash: [          ]   1.7% (used 18064 bytes from 1048576 bytes)
Building .pio/build/olimex_e407/firmware.bin
======================================================================== [SUCCESS] Took 2.72 seconds ========================================================================

Solution:

You need to specify a debug_tool in platformio.ini. For STM32 processors, a typical choice is

debug_tool = stlink

A list of options for debug_tool is available here.

Note that you can NOT debug many boards via the USB port. You can not debug boards attached via serial-to-USB converter (like many Arduino boards). Your board need to have a proper debugger on-board (like an stlink which is integrated on many STM32 eval boards) or you need to use an external debugger.

Note: If you need more flexibility, see Minimal STM32 HardwareTimer PlatformIO / Arduino timer interrupt blink example where we show how to use HardwareTimer instead of TimerInterrupt_Generic. Note that TimerInterrupt_Generic uses HardwareTimer internally.

This is a minimal example of using timer interrupts on PlatformIO / Arduino using the TimerInterrupt_Generic library which runs on the Olimex E407. It will run on almost any STM32 processor but you might need to adjust PC13 to the PIN connected to the LED. The example will blink the LED once per second.

#include <Arduino.h>
#include <TimerInterrupt_Generic.h>

STM32Timer tim1(TIM1);
bool ledOn = false;

void OnTimer1Interrupt() {
    ledOn = !ledOn;
    digitalWrite(PC13, ledOn ? LOW : HIGH);
}

void setup() {
    pinMode(PC13, OUTPUT);
    // Enable TIM4
    
    tim1.attachInterruptInterval(500000, OnTimer1Interrupt);
}

void loop() {
}

Now add

lib_deps =
     khoih.prog/TimerInterrupt_Generic @ ^1.7.0

to your platformio.ini. My full platformio.ini looks like this:

[env:olimex_e407]
platform = ststm32
board = olimex_e407
framework = arduino
lib_deps =
     khoih.prog/TimerInterrupt_Generic @ ^1.7.0

This code will make the Olimex E407 LED blink.

#include <Arduino.h>

void setup() {
    pinMode(PC13, OUTPUT);
}

void loop() {
    digitalWrite(PC13, LOW);
    delay(500);
    digitalWrite(PC13, HIGH);
    delay(500);
}

Problem

You are trying to run a firmware on the Olimex E407 that blinks the builtin green status LED. You code uses LED_BUILTIN similar to this:

#include <Arduino.h>

void setup() {
    pinMode(LED_BUILTIN, OUTPUT);
}

void loop() {
    digitalWrite(LED_BUILTIN, LOW);
    delay(500);
    digitalWrite(LED_BUILTIN, HIGH);
    delay(500);
}

but when you upload the code onto the board, the LED does not blink and stays off.

Solution

Instead of LED_BUILTIN, use PC13 – the pin the LED is connected to (which you can see on the Olimex E407 schematic:

#include <Arduino.h>

void setup() {
    pinMode(PC13, OUTPUT);
}

void loop() {
    digitalWrite(PC13, LOW);
    delay(500);
    digitalWrite(PC13, HIGH);
    delay(500);
}

Problem:

While trying to program your STM32 board using stlink and PlatformIO (most programmers integrated onto a development board are STLink programmers), you see this error message:

xPack OpenOCD, x86_64 Open On-Chip Debugger 0.11.0-00155-ge392e485e (2021-03-15-16:43)
Licensed under GNU GPL v2
For bug reports, read
        http://openocd.org/doc/doxygen/bugs.html
debug_level: 1

hla_swd
Error: libusb_open() failed with LIBUSB_ERROR_ACCESS
Error: open failed
in procedure 'program'
** OpenOCD init failed **
shutdown command invoked

Solution:

You need to setup the correct permissions for the STLink usb devices – in other words, install the correct stlink udev rules files. On Ubuntu, install stlink-tools using

sudo apt -y install stlink-tools
sudo systemctl restart udev

After that, unplug your stlink (or development board) for 5 seconds and plugin it in again. This will cause the new device permissions to take effect.

Now you can retry uploading the firmware from PlatformIO.