#include "main.h"
#include "generic_macros.h"
#include "dht11.h"

static struct SysTickConfig stc;
static uint32_t *systick_base = (uint32_t *) SysTick_BASE;

static void wait(uint32_t wait_us)
{
	int target_time = *(systick_base+8);
	target_time -= wait_us << 4;

	while (*(systick_base+8) > target_time) {}
}

static void dht11_save_systick_state(void)
{
	stc.ctrl = *(systick_base + 0);
	stc.load = *(systick_base + 4);
	stc.val  = *(systick_base + 8);
}

static void dht11_load_systick_state(void)
{
	*(systick_base + 4) = stc.load;
	*(systick_base + 8) = stc.val;
	*(systick_base + 0) = stc.ctrl;
}

static void dht11_init_systick(void)
{
	dht11_save_systick_state();

	*(systick_base + 0) = 0x5;      // disable /8 prescaler, no interrupts, enable counting
	*(systick_base + 4) = 0xFFFFFF; // load largest possible value

	// verify value load
	if (*(systick_base + 8) == 0)
		PANIC(0x4000);
}

static size_t dht11_measure_high_duration(void)
{
	int current_time = *(systick_base+8);
	SKIP_HIGH;

	// elapsed_time > 49us ? 1 : 0
	return (current_time - *(systick_base+8)) > (49 << 4);
}

static void dht11_read_value(struct DHT11_Data *data)
{
	dht11_init_systick();

	register uint8_t read_register = 0;

	GPIOD->BSRR = GPIO_PIN_11;       // enable DHT11
	wait(50000);                     // hold HIGH for 50 ms
	GPIOD->BSRR = GPIO_PIN_11 << 16; // start signal
	wait(30000);                     // hold it for 30 ms
	GPIOD->BSRR = GPIO_PIN_11;       // pull up, DHT will now take control over the connection

	// switch GPIOD 11 to input mode
	GPIOD->MODER &= 0xFF3FFFFF;

	// read transmission start sequence from DHT11
	SKIP_HIGH;
	SKIP_LOW;
	SKIP_HIGH;

	// read humidity integral
	FILL_REGISTER;
	data->humid_integral = read_register;

	// read humidity decimal
	FILL_REGISTER;
	data->humid_decimal = read_register;

	// read temperature integral
	FILL_REGISTER;
	data->temp_integral = read_register;

	// read temperature decimal
	FILL_REGISTER;
	data->temp_decimal = read_register;

	// read crc
	FILL_REGISTER;
	data->crc = read_register;

	dht11_load_systick_state();
}

void dht11_show_both(void)
{
	struct DHT11_Data data;
	dht11_read_value(&data);
}