RTOS for embedded systems

An open source firmware development framework that includes RTOS and drivers. Features include:

• Uses GCC + newlib and no extra dependencies
• Unified API across architectures
• RTOS scheduling is round robin with 1ms time slice

Feature support matrix

ARCH	Clock	Task	Mutex	Timer	Queue	GPIO	UART	SPI	I2C
stm32f0	48Mhz	yes	-	-	-	yes	yes	-	-
stm32f1	72Mhz	yes	-	-	-	yes	yes	-	-
stm32f3	72MHz	yes	-	-	-	yes	yes	-	-
stm32f7	216MHz	yes	-	-	-	yes	-	-	-

Build

Install packages arm-none-eabi-gcc, st-link, openocd (assuming Ubuntu):

$ apt-get install gcc-arm-none-eabi binutils-arm-none-eabi gdb-arm-none-eabi openocd stlink-tools

Build example firmware:

$ make -C examples/blinky clean all ARCH=stm32f1

To flash a firmware, connect your board and run:

$ make -C examples/blinky flash

API Reference

• Task management
  • rtos_init(); - must be the first function called by main()
  • rtos_task_create(fn, data, stacksize); - create task
  • rtos_schedule(); - start task scheduler, do not return
• Utility
  • rtos_msleep(ms); - sleep ms milliseconds
  • rtos_ram_free(); - return available RAM in bytes
  • rtos_ram_used(); - return used RAM in bytes
• GPIO
  • PIN(bank, num); - declare a GPIO pin: uint16_t pin = PIN('A', 5);
  • gpio_init(pin, mode, type, speed, pull, af); - init GPIO pin
  • gpio_on(pin); - set GPIO pin on
  • gpio_off(pin); - set GPIO pin off
  • gpio_toggle(pin); - toggle GPIO pin
  • gpio_input(pin); - (convenience) set input mode on a GPIO pin
  • gpio_output(pin); - (convenience) set output mode on a GPIO pin
• UART
  • uart_init(uart, tx_pin, rx_pin, baud); - initialise UART
  • uart_write_byte(uart, byte); - write one byte
  • uart_write_buf(uart, buf, len); - write buffer
  • uart_read_ready(uart); - return non-0 if UART can be read
  • uart_read_byte(uart); - read one byte

Debugging

In order to debug, first run openocd in one terminal:

$ make -C examples/blinky ARCH=stm32f3 openocd

In another terminal, build with DEBUG=1 and start a GDB debugger:

$ make -C examples/blinky ARCH=stm32f3 DEBUG=1 make clean all gdb

By default, GDB breakpoints in main(). Tip: use layout split GDB command for a handy source + disassembly display mode.

The DEBUG=1 adds a --specs rdimon linker flag, which enables a semihosting feature on ARM. That means, all stdio functions like printf() will be retargeted to an openocd console output - useful for a quick printf-debugging