/* firmware template for STM8S microcontroller
 * Copyright (C) 2019-2020 King Kévin <kingkevin@cuvoodoo.info>
 * SPDX-License-Identifier: GPL-3.0-or-later
 */
#include <stdint.h>
#include <stdbool.h>
#include "stm8s.h"

// get length of array
#define ARRAY_LENGTH(x) (sizeof(x) / sizeof((x)[0]))

// blocking wait (in 10 us steps, up to UINT32_MAX / 10)
static void wait_10us(uint32_t us10)
{
	us10 = ((us10 / (1 << CLK->CKDIVR.fields.HSIDIV)) * 1000) / 206; // calibrated for 1 ms
	for (volatile uint32_t t = 0; t < us10; t++); // burn energy
}

void main(void)
{
	sim(); // disable interrupts (while we reconfigure them)

	CLK->CKDIVR.fields.HSIDIV = CLK_CKDIVR_HSIDIV_DIV0; // don't divide internal 16 MHz clock
	CLK->CKDIVR.fields.CPUDIV = CLK_CKDIVR_CPUDIV_DIV0; // don't divide CPU frequency to 16 MHz
	while (!CLK->ICKR.fields.HSIRDY); // wait for internal oscillator to be ready

	// configure auto-wakeup (AWU) to be able to refresh the watchdog
	// 128 kHz LSI used by default in option bytes CKAWUSEL
	// we skip measuring the LS clock frequency since there is no need to be precise
	AWU->TBR.fields.AWUTB = 10; // interval range: 128-256 ms
	AWU->APR.fields.APR = 0x3e; // set time to 256 ms
	AWU_CSR |= AWU_CSR_AWUEN; // enable AWU (start only when entering wait or active halt mode)

	// configure independent watchdog (very loose, just it case the firmware hangs)
	IWDG->KR.fields.KEY = IWDG_KR_KEY_REFRESH; // reset watchdog
	IWDG->KR.fields.KEY = IWDG_KR_KEY_ENABLE; // start watchdog
	IWDG->KR.fields.KEY = IWDG_KR_KEY_ACCESS; // allows changing the prescale
	IWDG->PR.fields.PR = IWDG_PR_DIV256; // set prescale to longest time (1.02s)
	IWDG->KR.fields.KEY = IWDG_KR_KEY_REFRESH; // reset watchdog

	rim(); // re-enable interrupts
	bool action = false; // if an action has been performed
	while (true) {
		IWDG_KR = IWDG_KR_KEY_REFRESH; // reset watchdog
		if (action) { // something has been performed, check if other flags have been set meanwhile
			action = false; // clear flag
		} else { // nothing down
			wfi(); // go to sleep (wait for any interrupt, including periodic AWU)
		}
	}
}

void awu(void) __interrupt(IRQ_AWU) // auto wakeup
{
	volatile uint8_t awuf = AWU_CSR; // clear interrupt flag by reading it (reading is required, and volatile prevents compiler optimization)
	// let the main loop kick the dog
}