/** library to query measurements from Aosong DHT11 temperature and relative humidity sensor * @file * @author King Kévin * @copyright SPDX-License-Identifier: GPL-3.0-or-later * @date 2017-2020 * @note peripherals used: timer channel @ref sensor_dht11_timer */ /* standard libraries */ #include // standard integer types /* STM32 (including CM3) libraries */ #include // Cortex M3 utilities #include // interrupt handler #include // real-time control clock library #include // general purpose input output library #include // timer utilities /* own libraries */ #include "sensor_dht11.h" // PZEM electricity meter header and definitions #include "global.h" // common methods /** @defgroup sensor_dht11_timer timer peripheral used to measure signal timing for bit decoding * @{ */ #define SENSOR_DHT11_TIMER 3 /**< timer peripheral */ #define SENSOR_DHT11_CHANNEL 1 /**< channel used as input capture */ #define SENSOR_DHT11_JITTER 0.1 /**< signal timing jitter tolerated in timing */ /** @} */ volatile bool sensor_dht11_measurement_received = false; /** communication states */ volatile enum sensor_dht11_state_t { SENSOR_DHT11_OFF, // no request has started SENSOR_DHT11_HOST_START, // host starts request (and waits >18ms) SENSOR_DHT11_HOST_STARTED, // host started request and waits for slave answer SENSOR_DHT11_SLAVE_START, // slave responds to request and puts signal low for 80 us and high for 80 us SENSOR_DHT11_SLAVE_BIT, // slave is sending bit by putting signal low for 50 us and high (26-28 us = 0, 70 us = 1) SENSOR_DHT11_MAX } sensor_dht11_state = SENSOR_DHT11_OFF; /**< current communication state */ /** the bit number being sent (MSb first), up to 40 */ volatile uint8_t sensor_dht11_bit = 0; /** the 40 bits (5 bytes) being sent by the device */ volatile uint8_t sensor_dht11_bits[5] = {0}; /** reset all states */ static void sensor_dht11_reset(void) { // reset states sensor_dht11_state = SENSOR_DHT11_OFF; sensor_dht11_bit = 0; sensor_dht11_measurement_received = false; gpio_set(TIM_CH_PORT(SENSOR_DHT11_TIMER,SENSOR_DHT11_CHANNEL), TIM_CH_PIN(SENSOR_DHT11_TIMER,SENSOR_DHT11_CHANNEL)); // idle is high (using pull-up resistor), pull-up before setting as output else the signal will be low for short gpio_set_mode(TIM_CH_PORT(SENSOR_DHT11_TIMER,SENSOR_DHT11_CHANNEL), GPIO_MODE_OUTPUT_2_MHZ, GPIO_CNF_OUTPUT_OPENDRAIN, TIM_CH_PIN(SENSOR_DHT11_TIMER,SENSOR_DHT11_CHANNEL)); // setup GPIO pin as output (host starts communication before slave replies) timer_ic_disable(TIM(SENSOR_DHT11_TIMER), TIM_IC(SENSOR_DHT11_CHANNEL)); // enable capture interrupt only when receiving data timer_disable_counter(TIM(SENSOR_DHT11_TIMER)); // disable timer } void sensor_dht11_setup(void) { // setup timer to measure signal timing for bit decoding (use timer channel as input capture) rcc_periph_clock_enable(RCC_TIM_CH(SENSOR_DHT11_TIMER,SENSOR_DHT11_CHANNEL)); // enable clock for GPIO peripheral rcc_periph_clock_enable(RCC_TIM(SENSOR_DHT11_TIMER)); // enable clock for timer peripheral rcc_periph_reset_pulse(RST_TIM(SENSOR_DHT11_TIMER)); // reset timer state timer_set_mode(TIM(SENSOR_DHT11_TIMER), TIM_CR1_CKD_CK_INT, TIM_CR1_CMS_EDGE, TIM_CR1_DIR_UP); // set timer mode, use undivided timer clock,edge alignment (simple count), and count up timer_set_prescaler(TIM(SENSOR_DHT11_TIMER), 20 - 1); // set the prescaler so this 16 bits timer allows to wait for 18 ms for the start signal ( 1/(72E6/20/(2**16))=18.20ms ) timer_ic_set_input(TIM(SENSOR_DHT11_TIMER), TIM_IC(SENSOR_DHT11_CHANNEL), TIM_IC_IN_TI(SENSOR_DHT11_CHANNEL)); // configure ICx to use TIn timer_ic_set_filter(TIM(SENSOR_DHT11_TIMER), TIM_IC(SENSOR_DHT11_CHANNEL), TIM_IC_OFF); // use no filter input (precise timing needed) timer_ic_set_polarity(TIM(SENSOR_DHT11_TIMER), TIM_IC(SENSOR_DHT11_CHANNEL), TIM_IC_FALLING); // capture on rising edge timer_ic_set_prescaler(TIM(SENSOR_DHT11_TIMER), TIM_IC(SENSOR_DHT11_CHANNEL), TIM_IC_PSC_OFF); // don't use any prescaler since we want to capture every pulse timer_clear_flag(TIM(SENSOR_DHT11_TIMER), TIM_SR_UIF); // clear flag timer_update_on_overflow(TIM(SENSOR_DHT11_TIMER)); // only use counter overflow as UEV source (use overflow as start time or timeout) timer_enable_irq(TIM(SENSOR_DHT11_TIMER), TIM_DIER_UIE); // enable update interrupt for timer timer_clear_flag(TIM(SENSOR_DHT11_TIMER), TIM_SR_CCIF(SENSOR_DHT11_CHANNEL)); // clear input compare flag timer_enable_irq(TIM(SENSOR_DHT11_TIMER), TIM_DIER_CCIE(SENSOR_DHT11_CHANNEL)); // enable capture interrupt nvic_enable_irq(NVIC_TIM_IRQ(SENSOR_DHT11_TIMER)); // catch interrupt in service routine sensor_dht11_reset(); // reset state } bool sensor_dht11_measurement_request(void) { if (sensor_dht11_state != SENSOR_DHT11_OFF) { // not the right state to start (wait up until timeout to reset state) return false; } if (gpio_get(TIM_CH_PORT(SENSOR_DHT11_TIMER,SENSOR_DHT11_CHANNEL), TIM_CH_PIN(SENSOR_DHT11_TIMER,SENSOR_DHT11_CHANNEL)) == 0) { // signal should be high per default return false; } if (TIM_CR1(TIM(SENSOR_DHT11_TIMER)) & (TIM_CR1_CEN)) { // timer should be off return false; } sensor_dht11_reset(); // reset states // send start signal (pull low for > 18 ms) gpio_clear(TIM_CH_PORT(SENSOR_DHT11_TIMER,SENSOR_DHT11_CHANNEL), TIM_CH_PIN(SENSOR_DHT11_TIMER,SENSOR_DHT11_CHANNEL)); // set signal to low timer_set_counter(TIM(SENSOR_DHT11_TIMER), 0); // reset timer counter timer_enable_counter(TIM(SENSOR_DHT11_TIMER)); // enable timer to wait for 18 ms until overflow sensor_dht11_state = SENSOR_DHT11_HOST_START; // remember we started sending signal return true; } struct sensor_dht11_measurement_t sensor_dht11_measurement_decode(void) { struct sensor_dht11_measurement_t measurement = { 0xff, 0xff }; // measurement to return if (sensor_dht11_bit < 40) { // not enough bits received return measurement; } if ((uint8_t)(sensor_dht11_bits[0] + sensor_dht11_bits[1] + sensor_dht11_bits[2] + sensor_dht11_bits[3]) != sensor_dht11_bits[4]) { // error in checksum (not really parity bit, as mentioned in the datasheet) return measurement; } // calculate measured values (byte 1 and 3 should be the factional value but they are always 0) measurement.humidity = sensor_dht11_bits[0]; measurement.temperature = sensor_dht11_bits[2]; return measurement; } /** interrupt service routine called for timer */ void TIM_ISR(SENSOR_DHT11_TIMER)(void) { if (timer_get_flag(TIM(SENSOR_DHT11_TIMER), TIM_SR_UIF)) { // overflow update event happened timer_clear_flag(TIM(SENSOR_DHT11_TIMER), TIM_SR_UIF); // clear flag if (sensor_dht11_state == SENSOR_DHT11_HOST_START) { // start signal sent gpio_set_mode(TIM_CH_PORT(SENSOR_DHT11_TIMER,SENSOR_DHT11_CHANNEL), GPIO_MODE_INPUT, GPIO_CNF_INPUT_FLOAT, TIM_CH_PIN(SENSOR_DHT11_TIMER,SENSOR_DHT11_CHANNEL)); // switch pin to input (the external pull up with also set the signal high) sensor_dht11_state = SENSOR_DHT11_HOST_STARTED; // switch to next state timer_ic_enable(TIM(SENSOR_DHT11_TIMER), TIM_IC(SENSOR_DHT11_CHANNEL)); // enable capture interrupt only when receiving data } else { // timeout occurred sensor_dht11_reset(); // reset states } } else if (timer_get_flag(TIM(SENSOR_DHT11_TIMER), TIM_SR_CCIF(SENSOR_DHT11_CHANNEL))) { // edge detected on input capture uint16_t time = TIM_CCR(SENSOR_DHT11_TIMER,SENSOR_DHT11_CHANNEL); // save captured bit timing (this clear also the flag) timer_set_counter(TIM(SENSOR_DHT11_TIMER), 0); // reset timer counter time = (time * 1E6) / (rcc_ahb_frequency / (TIM_PSC(TIM(SENSOR_DHT11_TIMER)) + 1)); // calculate time in us switch (sensor_dht11_state) { case (SENSOR_DHT11_HOST_STARTED): // the host query data and the slave is responding sensor_dht11_state = SENSOR_DHT11_SLAVE_START; // set new state break; case (SENSOR_DHT11_SLAVE_START): // the slave sent the start signal if (time >= ((80 + 80) * (1 - SENSOR_DHT11_JITTER)) && time <= ((80 + 80)*(1 + SENSOR_DHT11_JITTER))) { // response time should be 80 us low and 80 us high sensor_dht11_state = SENSOR_DHT11_SLAVE_BIT; // set new state } else { goto error; } break; case (SENSOR_DHT11_SLAVE_BIT): // the slave sent a bit if (sensor_dht11_bit >= 40) { // no bits should be received after 40 bits goto error; } if (time >= ((50 + 26) * (1 - SENSOR_DHT11_JITTER)) && time <= ((50 + 28) * (1 + SENSOR_DHT11_JITTER))) { // bit 0 time should be 50 us low and 26-28 us high sensor_dht11_bits[sensor_dht11_bit / 8] &= ~(1 << (7 - (sensor_dht11_bit % 8))); // clear bit } else if (time >= ((50 + 70)*(1 - SENSOR_DHT11_JITTER)) && time <= ((50 + 70) * (1 + SENSOR_DHT11_JITTER))) { // bit 1 time should be 50 us low and 70 us high sensor_dht11_bits[sensor_dht11_bit / 8] |= (1 << (7 - (sensor_dht11_bit % 8))); // set bit } else { goto error; } sensor_dht11_bit++; if (sensor_dht11_bit >= 40) { // all bits received sensor_dht11_reset(); // reset states sensor_dht11_bit = 40; // signal decoder all bits have been received sensor_dht11_measurement_received = true; // signal user all bits have been received } break; default: // unexpected state error: sensor_dht11_reset(); // reset states } } else { // no other interrupt should occur while (true); // unhandled exception: wait for the watchdog to bite } }