/* ****************************************************************************
*
* 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 "platform_rmt.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, PLATFORM_RMT_INTR_FLAGS ) == ESP_OK) {
rmt_get_ringbuf_handle( 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;
}