STM32L476_MiniOS

Demonstration: How to implement a preemptive multitasking OS on embedded devices.

Contribution:

• Contribution
• Development
• What is this about?
• What is it not?
• How to port this to another platform?
• About

Contribution

• If you want to port this implementation fork me
• If you have improvements at your hand send me an PR

Development

• Hardware: STM32L476G-DISCO Board
• For development the STM32Cube IDE is used
  • gcc
• To get a highlevel API the Board BSP from ST is used
• Debug Printouts on UART2:
  • can be activated via switch in Usercode/debug.h or with compiler define.

  #define DEBUG_PRINT
  

  • Setting:
    • Baudrate: 9600
    • Databits: 8
    • Stopbits: 1
    • Parity: None

What is this about?

• This is a demonstration how to create a preemptive multitasking system which can run threads (using setjmp/longjmp, and a timer for preemptive scheduling)

What is it not?

• A implementation to use in production. If you need preemptive multithreading use RTOS or something similar.
• Portable to other platforms (Stackframe definition specific for ARM Cortex-M4)

How to port this to another platform?

1. You need everything in Usercode/Concurrency
2. remove or implement methods according to Usercode/debug.c
3. Adaptions in scheduler.c
   1. redefine t_stackFrame according to your platform
   2. allocate stackframe correct in allocateStack
   3. change this to match your platform
      1. if you not using cmsis_gcc.h find out how to set/get the stackpointer
      2. yield ... exit pending interrupt
      3. void TIM1_CC_IRQHandler() - this is the timer interupt for preemptive scheduling
      4. timers_init() - creating a timer which calls the the timer interrupt at a rate of TIMESLICE_MS

About

• OS Implementation:
  • Preemptive Scheduling: Usercode/Concurrency/scheduler.c
  • Synchronisation Mechanism via counting semaphores: Usercode/Concurrency/semaphore.c
  • Demo Usage: Usercode/usercode.c
    • To enable/disable synchronization change #define SEM_DEMO at start of usercode.c
• Basic Usage Example - printout stuff to console + green and red LED should flash in parallel forever:

void flashGreenThreadForever() {
	while (true) {
		BSP_LED_Toggle(LED_GREEN);
		scheduler_sleep(50);
	}
}

void flashRedThreadForever() {
	while (true) {
		BSP_LED_Toggle(LED_RED);
		scheduler_sleep(50);
	}
}

void printSome() {
	DEBUG_PRINTF("Test 1 ... ");
	DEBUG_PRINTF("Test 2 ... ");
	DEBUG_PRINTF("Test 3 ... ");
	DEBUG_PRINTF("Test 4 ... ");
	DEBUG_PRINTF("Test 5 ... ");
}

void runExample() {
	scheduler_init();
	scheduler_startThread(&printSome);
	scheduler_startThread(&flashGreenThreadForever);
	scheduler_startThread(&flashRedThreadForever);
}