tasks

/*
 * Generate time slots for stm32f1
 */
#include <libopencm3/stm32/rcc.h>
#include <libopencm3/stm32/gpio.h>
#include <libopencm3/stm32/timer.h>
#include <libopencm3/cm3/nvic.h>

#define SLOT_LEN 10
#define SMALLEST_SLOT_TIME 3
static volatile uint32_t t_slot = 0;
static volatile uint32_t ms[SLOT_LEN];

static void sys_init(void) {
	rcc_clock_setup_in_hse_8mhz_out_72mhz(); // Use this for "blue pill"
	/* Enable GPIOA clock. */
	rcc_periph_clock_enable(RCC_GPIOA);
	rcc_periph_clock_enable(RCC_AFIO);
	/* Set GPIO1 (in GPIO port A) to 'output alternate function push-pull'. */
	gpio_set_mode(GPIOA, GPIO_MODE_OUTPUT_50_MHZ, GPIO_CNF_OUTPUT_ALTFN_PUSHPULL, GPIO1);
	// timer init
	rcc_periph_clock_enable(RCC_TIM2);
	TIM2_SR = 0;
	TIM2_PSC = 17;
	TIM2_ARR = ms[t_slot];
	TIM2_CCR2 = 1;
	// set up interrupt
	TIM2_DIER = TIM_DIER_UIE;
	nvic_enable_irq(NVIC_TIM2_IRQ);
	// set output to PWM1 mode
	TIM2_CCMR1 = TIM_CCMR1_OC2M_PWM1;
	TIM2_CCER = TIM_CCER_CC2E;
}

void tim2_isr() {
	TIM2_SR &= ~TIM_SR_UIF;
	if (t_slot==SLOT_LEN) t_slot = 0;
	TIM2_ARR = ms[t_slot++];
}

int main(void) {
	// set up time slot
	for (int i = 0; i < SLOT_LEN; i++)
		ms[i] = 4*i + SMALLEST_SLOT_TIME;
	sys_init();
	// enable timer
	TIM2_CR1 |= TIM_CR1_CEN;
	for (;;);
	return 0;
}