
/* ****************************************************************************
 *
 * 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, ESP_INTR_FLAG_LOWMED | ESP_INTR_FLAG_IRAM | ESP_INTR_FLAG_SHARED ) == 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;
}
