Fix incorrect check for CRC when reading temperature. Fix Celsius conversion. Preliminary support for programmable resolution.

main/ds18b20.c

@@ -76,6 +76,29 @@ static bool _is_init(const DS18B20_Info * ds18b20_info)
     return ok;
 }
 
+static bool _check_resolution(DS18B20_RESOLUTION resolution)
+{
+    return (resolution >= DS18B20_RESOLUTION_9_BIT) && (resolution <= DS18B20_RESOLUTION_12_BIT);
+}
+
+static float _decode_temp(uint8_t lsb, uint8_t msb, DS18B20_RESOLUTION resolution)
+{
+    float result = 0.0f;
+    if (_check_resolution(resolution))
+    {
+        // masks to remove undefined bits from result
+        static const uint8_t lsb_mask[4] = { ~0x03, ~0x02, ~0x01, ~0x00 };
+        uint8_t lsb_masked = lsb_mask[resolution - DS18B20_RESOLUTION_9_BIT] & lsb;
+        int16_t raw = (msb << 8) | lsb_masked;
+        result = raw / 16.0f;
+    }
+    else
+    {
+        ESP_LOGE(TAG, "Unsupported resolution %d", resolution);
+    }
+    return result;
+}
+
 DS18B20_Info * ds18b20_malloc(void)
 {
     DS18B20_Info * ds18b20_info = malloc(sizeof(*ds18b20_info));
@@ -109,6 +132,7 @@ void ds18b20_init(DS18B20_Info * ds18b20_info, OneWireBus * bus, OneWireBus_ROMC
         ds18b20_info->bus = bus;
         ds18b20_info->rom_code = rom_code;
         ds18b20_info->use_crc = false;
+        ds18b20_info->resolution = DS18B20_RESOLUTION_12_BIT;
         ds18b20_info->init = true;
     }
     else
@@ -149,7 +173,7 @@ float ds18b20_get_temp(DS18B20_Info * ds18b20_info)
 
             uint8_t temp_LSB = 0;
             uint8_t temp_MSB = 0;
-            if (ds18b20_info->use_crc)
+            if (!ds18b20_info->use_crc)
             {
                 // Without CRC:
                 temp_LSB = owb_read_byte(bus);
@@ -173,7 +197,7 @@ float ds18b20_get_temp(DS18B20_Info * ds18b20_info)
             }
 
             ESP_LOGD(TAG, "temp_LSB 0x%02x, temp_MSB 0x%02x", temp_LSB, temp_MSB);
-            temp = (float)(((temp_MSB << 8) + temp_LSB) >> 4);
+            temp = _decode_temp(temp_LSB, temp_MSB, ds18b20_info->resolution);
         }
         else
         {

main/ds18b20.h

@@ -40,16 +40,28 @@
 extern "C" {
 #endif
 
+/**
+ * @brief Symbols for the supported temperature resolution of the device.
+ */
+typedef enum
+{
+    DS18B20_RESOLUTION_9_BIT   = 9,   ///< 9-bit resolution, LSB bits 2,1,0 undefined
+    DS18B20_RESOLUTION_10_BIT  = 10,  ///< 10-bit resolution, LSB bits 1,0 undefined
+    DS18B20_RESOLUTION_11_BIT  = 11,  ///< 11-bit resolution, LSB bit 0 undefined
+    DS18B20_RESOLUTION_12_BIT  = 12,  ///< 12-bit resolution (default)
+} DS18B20_RESOLUTION;
+
 /**
  * @brief Structure containing information related to a single DS18B20 device connected
  * via a 1-Wire bus.
  */
 typedef struct
 {
-    bool init;                    ///< True if struct has been initialised, otherwise false.
+    bool init;                     ///< True if struct has been initialised, otherwise false
     bool use_crc;                  ///< True if CRC checks are to be used when retrieving information from a device on the bus
-    OneWireBus * bus;             ///< Pointer to 1-Wire bus information relevant to this device.
+    OneWireBus * bus;              ///< Pointer to 1-Wire bus information relevant to this device
-    OneWireBus_ROMCode rom_code;  ///< The ROM code used to address this device on the bus.
+    OneWireBus_ROMCode rom_code;   ///< The ROM code used to address this device on the bus
+    DS18B20_RESOLUTION resolution; ///< Temperature measurement resolution per reading
 } DS18B20_Info;
 
 /**

main/ds18b20_main.c

@@ -42,7 +42,7 @@
 
 void app_main()
 {
-    esp_log_level_set("*", ESP_LOG_INFO);
+    esp_log_level_set("*", ESP_LOG_DEBUG);
 
     // Create a 1-Wire bus
 #ifdef USE_STATIC

main/owb.c

@@ -42,28 +42,27 @@ static const char * TAG = "owb";
 /// @cond ignore
 struct _OneWireBus_Timing
 {
-    int A, B, C, D, E, F, G, H, I, J;
+    uint32_t A, B, C, D, E, F, G, H, I, J;
 };
 //// @endcond
 
-// 1-Wire timing delays (standard) in ticks (quarter-microseconds).
+// 1-Wire timing delays (standard) in microseconds.
+// Labels and values are from https://www.maximintegrated.com/en/app-notes/index.mvp/id/126
 static const struct _OneWireBus_Timing _StandardTiming = {
-        6 * 4,
+        6,    // A - read/write "1" master pull DQ low duration
-        64 * 4,
+        64,   // B - write "0" master pull DQ low duration
-        60 * 4,
+        60,   // C - write "1" master pull DQ high duration
-        10 * 4,
+        10,   // D - write "0" master pull DQ high duration
-        9 * 4,
+        9,    // E - read master pull DQ high duration
-        55 * 4,
+        55,   // F - complete read timeslot + 10ms recovery
-        0,        // G
+        0,    // G - wait before reset
-        480 * 4,  // H
+        480,  // H - master pull DQ low duration
-        70 * 4,   // I
+        70,   // I - master pull DQ high duration
-        410 * 4,  // J
+        410,  // J - complete presence timeslot + recovery
 };
 
-static void _tick_delay(int ticks)
+static void _us_delay(uint32_t time_us)
 {
-    // Each tick is 0.25 microseconds.
-    float time_us = ticks / 4.0;
     ets_delay_us(time_us);
 }
 
@@ -90,7 +89,7 @@ bool _is_init(const OneWireBus * bus)
 }
 
 /**
- * @brief Generate a 1-Wire reset.
+ * @brief Generate a 1-Wire reset (initialization).
  * @param[in] bus Initialised bus instance.
  * @return true if device is present, otherwise false.
  */
@@ -101,15 +100,15 @@ static bool _reset(const OneWireBus * bus)
     {
         gpio_set_direction(bus->gpio, GPIO_MODE_OUTPUT);
 
-        _tick_delay(bus->timing->G);
+        _us_delay(bus->timing->G);
         gpio_set_level(bus->gpio, 0);  // Drive DQ low
-        _tick_delay(bus->timing->H);
+        _us_delay(bus->timing->H);
         gpio_set_level(bus->gpio, 1);  // Release the bus
-        _tick_delay(bus->timing->I);
+        _us_delay(bus->timing->I);
 
         gpio_set_direction(bus->gpio, GPIO_MODE_INPUT);
         int level1 = gpio_get_level(bus->gpio);
-        _tick_delay(bus->timing->J);   // Complete the reset sequence recovery
+        _us_delay(bus->timing->J);   // Complete the reset sequence recovery
         int level2 = gpio_get_level(bus->gpio);
 
         present = (level1 == 0) && (level2 == 1);   // Sample for presence pulse from slave
@@ -131,9 +130,9 @@ static void _write_bit(const OneWireBus * bus, int bit)
         int delay2 = bit ? bus->timing->B : bus->timing->D;
         gpio_set_direction(bus->gpio, GPIO_MODE_OUTPUT);
         gpio_set_level(bus->gpio, 0);  // Drive DQ low
-        _tick_delay(delay1);
+        _us_delay(delay1);
         gpio_set_level(bus->gpio, 1);  // Release the bus
-        _tick_delay(delay2);
+        _us_delay(delay2);
     }
 }
 
@@ -148,13 +147,13 @@ static int _read_bit(const OneWireBus * bus)
     {
         gpio_set_direction(bus->gpio, GPIO_MODE_OUTPUT);
         gpio_set_level(bus->gpio, 0);  // Drive DQ low
-        _tick_delay(bus->timing->A);
+        _us_delay(bus->timing->A);
         gpio_set_level(bus->gpio, 1);  // Release the bus
-        _tick_delay(bus->timing->E);
+        _us_delay(bus->timing->E);
 
         gpio_set_direction(bus->gpio, GPIO_MODE_INPUT);
         int level = gpio_get_level(bus->gpio);
-        _tick_delay(bus->timing->F);   // Complete the timeslot and 10us recovery
+        _us_delay(bus->timing->F);   // Complete the timeslot and 10us recovery
         result = level & 0x01;
     }
     return result;