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- /* ****************************************************************************
- *
- * ESP32 platform interface for DHT temperature & humidity sensors
- *
- * Copyright (c) 2017, Arnim Laeuger
- *
- * Permission is hereby granted, free of charge, to any person obtaining a copy
- * of this software and associated documentation files (the "Software"), to deal
- * in the Software without restriction, including without limitation the rights
- * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
- * copies of the Software, and to permit persons to whom the Software is
- * furnished to do so, subject to the following conditions:
- *
- * The above copyright notice and this permission notice shall be included in all
- * copies or substantial portions of the Software.
- *
- * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
- * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
- * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
- * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
- * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
- * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
- * SOFTWARE.
- * ****************************************************************************/
- #include "platform.h"
- #include "driver/rmt.h"
- #include "driver/gpio.h"
- #include "freertos/FreeRTOS.h"
- #include "freertos/task.h"
- #include "esp_log.h"
- #undef DHT_DEBUG
- // RX idle threshold [us]
- // needs to be larger than any duration occurring during bit slots
- // datasheet specs up to 200us for "Bus master has released time"
- #define DHT_DURATION_RX_IDLE (250)
- // zero bit duration threshold [us]
- // a high phase
- // * shorter than this is detected as a zero bit
- // * longer than this is detected as a one bit
- #define DHT_DURATION_ZERO (50)
- // grouped information for RMT management
- static struct {
- int channel;
- RingbufHandle_t rb;
- int gpio;
- } dht_rmt = {-1, NULL, -1};
- static void dht_deinit( void )
- {
- // drive idle level 1
- gpio_set_level( dht_rmt.gpio, 1 );
- rmt_rx_stop( dht_rmt.channel );
- rmt_driver_uninstall( dht_rmt.channel );
- platform_rmt_release( dht_rmt.channel );
- // invalidate channel and gpio assignments
- dht_rmt.channel = -1;
- dht_rmt.gpio = -1;
- }
- static int dht_init( uint8_t gpio_num )
- {
- // acquire an RMT module for RX
- if ((dht_rmt.channel = platform_rmt_allocate( 1 )) >= 0) {
- #ifdef DHT_DEBUG
- ESP_LOGI("dht", "RMT RX channel: %d", dht_rmt.channel);
- #endif
- rmt_config_t rmt_rx;
- rmt_rx.channel = dht_rmt.channel;
- rmt_rx.gpio_num = gpio_num;
- rmt_rx.clk_div = 80; // base period is 1us
- rmt_rx.mem_block_num = 1;
- rmt_rx.rmt_mode = RMT_MODE_RX;
- rmt_rx.rx_config.filter_en = true;
- rmt_rx.rx_config.filter_ticks_thresh = 30;
- rmt_rx.rx_config.idle_threshold = DHT_DURATION_RX_IDLE;
- if (rmt_config( &rmt_rx ) == ESP_OK) {
- if (rmt_driver_install( rmt_rx.channel, 512, 0 ) == ESP_OK) {
- rmt_get_ringbuf_handler( dht_rmt.channel, &dht_rmt.rb );
- dht_rmt.gpio = gpio_num;
- // use gpio for TX direction
- // drive idle level 1
- gpio_set_level( gpio_num, 1 );
- gpio_pullup_dis( gpio_num );
- gpio_pulldown_dis( gpio_num );
- gpio_set_direction( gpio_num, GPIO_MODE_INPUT_OUTPUT_OD );
- gpio_set_intr_type( gpio_num, GPIO_INTR_DISABLE );
- return PLATFORM_OK;
- }
- }
- platform_rmt_release( dht_rmt.channel );
- }
- return PLATFORM_ERR;
- }
- int platform_dht_read( uint8_t gpio_num, uint8_t wakeup_ms, uint8_t *data )
- {
- if (dht_init( gpio_num ) != PLATFORM_OK)
- return PLATFORM_ERR;
- // send start signal and arm RX channel
- TickType_t xDelay = pdMS_TO_TICKS( wakeup_ms ) > 0 ? pdMS_TO_TICKS( wakeup_ms ) : 1;
- gpio_set_level( gpio_num, 0 ); // pull wire low
- vTaskDelay( xDelay ); // time low phase
- rmt_rx_start( dht_rmt.channel, true ); // arm RX channel
- gpio_set_level( gpio_num, 1 ); // release wire
- // wait for incoming bit stream
- size_t rx_size;
- rmt_item32_t* rx_items = (rmt_item32_t *)xRingbufferReceive( dht_rmt.rb, &rx_size, pdMS_TO_TICKS( 100 ) );
- // default is "no error"
- // error conditions have to overwrite this with PLATFORM_ERR
- int res = PLATFORM_OK;
- if (rx_items) {
- #ifdef DHT_DEBUG
- ESP_LOGI("dht", "rx_items received: %d", rx_size);
- for (size_t i = 0; i < rx_size / 4; i++) {
- ESP_LOGI("dht", "level: %d, duration %d", rx_items[i].level0, rx_items[i].duration0);
- ESP_LOGI("dht", "level: %d, duration %d", rx_items[i].level1, rx_items[i].duration1);
- }
- #endif
- // we expect 40 bits of payload plus a response bit and two edges for start and stop signals
- // each bit on the wire consumes 2 rmt samples (and 2 rmt samples stretch over 4 bytes)
- if (rx_size >= (5*8 + 1+1) * 4) {
- // check framing
- if (rx_items[ 0].level0 == 1 && // rising edge of the start signal
- rx_items[ 0].level1 == 0 && rx_items[1].level0 == 1 && // response signal
- rx_items[41].level1 == 0) { // falling edge of stop signal
- // run through the bytes
- for (size_t byte = 0; byte < 5 && res == PLATFORM_OK; byte++) {
- size_t bit_pos = 1 + byte*8;
- data[byte] = 0;
- // decode the bits inside a byte
- for (size_t bit = 0; bit < 8; bit++, bit_pos++) {
- if (rx_items[bit_pos].level1 != 0) {
- // not a falling edge, terminate decoding
- res = PLATFORM_ERR;
- break;
- }
- // ignore duration of low level
- // data is sent MSB first
- data[byte] <<= 1;
- if (rx_items[bit_pos + 1].level0 == 1 && rx_items[bit_pos + 1].duration0 > DHT_DURATION_ZERO)
- data[byte] |= 1;
- }
- #ifdef DHT_DEBUG
- ESP_LOGI("dht", "data 0x%02x", data[byte]);
- #endif
- }
- // all done
- } else {
- // framing mismatch on start, response, or stop signals
- res = PLATFORM_ERR;
- }
- } else {
- // too few bits received
- res = PLATFORM_ERR;
- }
- vRingbufferReturnItem( dht_rmt.rb, (void *)rx_items );
- } else {
- // time out occurred, this indicates an unconnected / misconfigured bus
- res = PLATFORM_ERR;
- }
- dht_deinit();
- return res;
- }
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