dht_test/main.c

/*
 * This file is part of the libopencm3 project.
 *
 * Copyright (C) 2009 Uwe Hermann <uwe@hermann-uwe.de>
 *
 * This library is free software: you can redistribute it and/or modify
 * it under the terms of the GNU Lesser General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * This library is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public License
 * along with this library.  If not, see <http://www.gnu.org/licenses/>.
 */

#include <stdio.h>

#include <libopencm3/cm3/nvic.h>
#include <libopencm3/stm32/rcc.h>
#include <libopencm3/stm32/gpio.h>
#include <libopencm3/stm32/timer.h>

#include <SEGGER_RTT.h>

#define puts(s) SEGGER_RTT_WriteString(0, s);SEGGER_RTT_WriteString(0,"\n")

#define DHT_PORT GPIOB
#define DHT_PIN  GPIO0

enum DHT11_STATE {
	DHT11_STOP,  // Stop statemachine
	DHT11_START,  // We drive DATA Low for minimum 18ms and then drive it HIGH and start waiting for response
	DHT11_RESPONSE,  // Wait for DHT to drive DATA Low
	DHT11_DATA,  // Receiving data
	DHT11_END,  // Got last bit
	DHT11_TIMEOUT,  // Not response or got partial data only
};

int g_dht11_state = DHT11_STOP;

// 2 pulses are the DHT Response and last 40 are data pulses for 5 bytes
// so we have total of 42 pulses
#define DHT11_BIT_COUNT 42
int g_dht_i = 0;  // how many bits we have captured
uint16_t g_dht_vals[DHT11_BIT_COUNT] = {0};  // captured bit times in us


static void delay(int count)
{
	for (int i=0; i < count; i++) {
		__asm__("nop");
	}
}

static void gpio_setup(void)
{
	/* Enable GPIOA clock. */
	/* Manually: */
	// RCC_APB2ENR |= RCC_APB2ENR_IOPCEN;
	/* Using API functions: */
	rcc_periph_clock_enable(RCC_GPIOB);

	/* Set GPIO5 (in GPIO port A) to 'output push-pull'. */
	/* Manually: */
	// GPIOA_CRH = (GPIO_CNF_OUTPUT_PUSHPULL << (((5 - 8) * 4) + 2));
	// GPIOA_CRH |= (GPIO_MODE_OUTPUT_2_MHZ << ((5 - 8) * 4));
	/* Using API functions: */
	// DHT Data pin
	gpio_set_mode(DHT_PORT, GPIO_MODE_INPUT, GPIO_CNF_INPUT_PULL_UPDOWN, DHT_PIN);
	// Maple mini led
	gpio_set_mode(GPIOB, GPIO_MODE_OUTPUT_2_MHZ, GPIO_CNF_OUTPUT_PUSHPULL, GPIO1);
	// A random DEBUG pin we can toggle and measure with logic
	gpio_set_mode(GPIOB, GPIO_MODE_OUTPUT_2_MHZ, GPIO_CNF_OUTPUT_PUSHPULL, GPIO2);
}

// Onetime config of timer things that stay the same
static void tim_setup(void)
{
	nvic_enable_irq(NVIC_TIM3_IRQ);
	nvic_set_priority(NVIC_TIM3_IRQ, 1);  // interrupts will not work without it???

	rcc_periph_clock_enable(RCC_TIM3);
	rcc_periph_reset_pulse(RST_TIM3);

	// configure the timer to be a normal up counting timer, nothing fancy
	timer_set_mode(TIM3, TIM_CR1_CKD_CK_INT, TIM_CR1_CMS_EDGE, TIM_CR1_DIR_UP);
	timer_set_prescaler(TIM3, (rcc_apb1_frequency*2) / 1000000 - 1);  // set timer tickrate to 1mhz
	timer_set_period(TIM3, 0xffff);  // ~64 ms, DHT11 packet is never longer than 26ms

	timer_enable_irq(TIM3, TIM_DIER_UIE);  // overflow
	timer_enable_irq(TIM3, TIM_DIER_CC3IE);  // triggered when DHT drives DATA pin
}

void tim3_isr(void)
{
	// Timer overflow that should only happen if DHT11 does not answer
	if (timer_get_flag(TIM3, TIM_SR_UIF)) {
		timer_clear_flag(TIM3, TIM_SR_UIF);
		puts("overflow");
		g_dht11_state = DHT11_TIMEOUT;
		timer_disable_counter(TIM3);
	}

	else if (timer_get_flag(TIM3, TIM_SR_CC3IF))  // PB0 changed value
	{
		//gpio_toggle(GPIOB, GPIO2);

		// handle DHT11_END_START
		if (g_dht11_state == DHT11_START) {
			// Drive DATA pin high for a split second so that we have a nice sharp edge
			gpio_set(DHT_PORT, DHT_PIN);
			// Make the GPIO input so that we can wait for response
			// there is a external pull-up connected to the DATA pin
			// probably could use the internal pull-up also...
			gpio_set_mode(DHT_PORT, GPIO_MODE_INPUT, GPIO_CNF_INPUT_FLOAT, DHT_PIN);

			// setup timer input capture to wait for start response from dht11
			// need to disable input capture before we can configure it.
			timer_ic_disable(TIM3, TIM_IC3);
			timer_ic_set_input(TIM3, TIM_IC3, TIM_IC_IN_TI3);
			timer_ic_set_polarity(TIM3, TIM_IC3, TIM_IC_FALLING);
			timer_clear_flag(TIM3, TIM_SR_CC3IF);  // otherwise we will get a invalid interrupt
			timer_ic_enable(TIM3, TIM_IC3);

			//puts("waiting for response");
			g_dht11_state = DHT11_RESPONSE;
		}

		// DHT11 drove DATA low and has started talking to us
		else if (g_dht11_state == DHT11_RESPONSE) {
			// store time when DHT11 pulled DATA low
			g_dht_vals[g_dht_i++] = TIM_CCR3(TIM3);
			g_dht11_state = DHT11_DATA;
		}

		// DHT11 is sending data to us
		else {
			// store length of the data bit
			g_dht_vals[g_dht_i++] = TIM_CCR3(TIM3);
		}

		// Did we just capture our last bit?
		if (g_dht_i >= DHT11_BIT_COUNT) {
			// yes we did
			g_dht11_state = DHT11_END;
			timer_disable_counter(TIM3);
		}

		timer_clear_flag(TIM3, TIM_SR_CC3IF);
		//gpio_toggle(GPIOB, GPIO2);
	}

	// Should only happen if TIM_SR_CC3IF is too slow
	// at 72mhz it should never happen but could at lower cpu speeds
	if (timer_get_flag(TIM3, TIM_SR_CC3OF))
	{
		timer_clear_flag(TIM3, TIM_SR_CC3OF);
		//puts("we are too slow to read and clear timer input capture flags");
		g_dht11_state = DHT11_TIMEOUT;
		timer_disable_counter(TIM3);
	}

}

// Setup the timer and trigger DHT11 Start
static void dht_start(void)
{
	timer_disable_counter(TIM3);
	g_dht11_state = DHT11_STOP;
	g_dht_i = 0;

	// Setup DHT11_END_START trigger on output compare 1
	timer_set_counter(TIM3, 0);

	// capture compare channel must be disabled before we can configure it
	timer_ic_disable(TIM3, TIM_IC3);
	// set channel as output so that we can get an interrupt when OC3 values matches the timer counter
	timer_ic_set_input(TIM3, TIM_IC3, TIM_IC_OUT);
	// tick rate should be 1Mhz (via timer prescaler), so this should trigger in 20ms
	timer_set_oc_value(TIM3, TIM_OC3, 1000*20);
	// clear status flags so that we dont get any stray interrupts
	timer_clear_flag(TIM3, TIM_SR_CC3IF);
	// and make sure that we can get interrupts
	timer_ic_enable(TIM3, TIM_IC3);

	// Begin the statemachine
	g_dht11_state = DHT11_START;

	// Do DHT11_BEGIN_START aka drive DATA Low
	gpio_set_mode(DHT_PORT, GPIO_MODE_OUTPUT_2_MHZ, GPIO_CNF_OUTPUT_PUSHPULL, DHT_PIN);
	gpio_clear(DHT_PORT, DHT_PIN);

	// And start counting
	timer_enable_counter(TIM3);
}

// Parse received DHT11 bit timing data from g_dht_vals and print out pretty values
static void dht_parse_data(void) {
	int8_t data[5] = {0};
	uint8_t checksum = 0;
	int data_index = 0;
	int data_bit = 7;

	// create bytes from bits
	for (int i=2; i < DHT11_BIT_COUNT; i++){  // First 2 pulses are start of response, ignore them
		uint16_t bit_time = g_dht_vals[i] - g_dht_vals[i-1];

		// ~80us is 0 and ~120us is 1
		if (bit_time > 100) {
			data[data_index] |= 1 << data_bit;
		}
		data_bit--;
		if (data_bit < 0) {
			data_bit = 7;
			data_index++;
		}
	}

	for (int i = 0; i < 4; i++){
		checksum += data[i];
	}

	if (checksum == data[4]) {
		SEGGER_RTT_printf(0, "Humidity: %d.%d%%; Temperature: %d.%dC\n",
						  data[0], data[1], data[2], data[3]);
	} else {
		SEGGER_RTT_printf(0, "Checksum did not match, %x != %x\n", checksum, data[4]);
	}
}

// Just toggle the data pin, used only for debugging
//static void dht_start_signal(void)
//{
//	gpio_set_mode(DHT_PORT, GPIO_MODE_OUTPUT_2_MHZ, GPIO_CNF_OUTPUT_PUSHPULL, DHT_PIN);
//	gpio_clear(DHT_PORT, DHT_PIN);
//	delay(100000);
//	//delay(30000);
//	gpio_set(DHT_PORT, DHT_PIN);
//	delay(100);
//	gpio_set_mode(DHT_PORT, GPIO_MODE_INPUT, GPIO_CNF_INPUT_PULL_UPDOWN, DHT_PIN);
//}

int main(void)
{
	int i = 0;
	bool wait = false;
	puts("Start");
	rcc_clock_setup_pll(&rcc_hse_configs[RCC_CLOCK_HSE8_72MHZ]);
	gpio_setup();
	tim_setup();

	/* Blink the LED (PA5) on the board. */
	while (1) {
		/* Using API function gpio_toggle(): */
		gpio_toggle(GPIOB, GPIO1);	/* LED on/off */
		i++;
		SEGGER_RTT_printf(0, "Poll: %d\n", i);
		delay(10000000);
		dht_start();
		wait = true;
		while (wait) {
			switch (g_dht11_state) {
				case DHT11_END:
					dht_parse_data();
					// fall through
				case DHT11_TIMEOUT:
					wait = false;
			}
		}
	}

	return 0;
}