Support separate conversion start and temperature retrieval to allow for multiple devices to be used simultaneously.

README.md

@@ -21,6 +21,7 @@ This library includes:
  * CRC checks on ROM code and temperature data.
  * Programmable temperature measurement resolution (9, 10, 11 or 12-bit resolution).
  * Temperature conversion and retrieval.
+ * Separation of conversion and temperature retrieval to allow for simultaneous conversion across multiple devices.
 
 ## Documentation
 
@@ -51,7 +52,7 @@ Parts of this code are based on references provided to the public domain by Maxi
 
 The following features are anticipated but not yet implemented:
 
- * Simultaneous temperature conversion from multiple devices on the same bus - concurrency.
+ * Concurrency support (multiple tasks accessing devices on the same bus).
  * Alarm support.
  * EEPROM support.
  * Parasitic power support.

main/ds18b20.c

@@ -360,9 +360,9 @@ DS18B20_RESOLUTION ds18b20_read_resolution(DS18B20_Info * ds18b20_info)
     return resolution;
 }
 
-float ds18b20_get_temp(const DS18B20_Info * ds18b20_info)
+bool ds18b20_convert(const DS18B20_Info * ds18b20_info)
 {
-    float temp = 0.0f;
+    bool result = false;
     if (_is_init(ds18b20_info))
     {
         OneWireBus * bus = ds18b20_info->bus;
@@ -370,10 +370,42 @@ float ds18b20_get_temp(const DS18B20_Info * ds18b20_info)
         {
             // initiate a temperature measurement
             owb_write_byte(bus, DS18B20_FUNCTION_TEMP_CONVERT);
+            result = true;
+        }
+        else
+        {
+            ESP_LOGE(TAG, "ds18b20 device not responding");
+        }
+    }
+    return result;
+}
 
-            // wait at least maximum conversion time
-            _wait_for_conversion(ds18b20_info->resolution);
+void ds18b20_convert_all(const OneWireBus * bus)
+{
+    owb_reset(bus);
+    owb_write_byte(bus, OWB_ROM_SKIP);
+    owb_write_byte(bus, DS18B20_FUNCTION_TEMP_CONVERT);
+
+    // wait the maximum conversion duration
+    _wait_for_conversion(DS18B20_RESOLUTION_12_BIT);
+}
+
+void ds18b20_wait_for_conversion(const DS18B20_Info * ds18b20_info)
+{
+    if (_is_init(ds18b20_info))
+    {
+        _wait_for_conversion(ds18b20_info->resolution);
+    }
+}
 
+float ds18b20_read_temp(const DS18B20_Info * ds18b20_info)
+{
+    float temp = 0.0f;
+    if (_is_init(ds18b20_info))
+    {
+        OneWireBus * bus = ds18b20_info->bus;
+        if (_address_device(ds18b20_info))
+        {
             // read measurement
             _address_device(ds18b20_info);
             owb_write_byte(bus, DS18B20_FUNCTION_SCRATCHPAD_READ);
@@ -411,6 +443,23 @@ float ds18b20_get_temp(const DS18B20_Info * ds18b20_info)
             ESP_LOGE(TAG, "ds18b20 device not responding");
         }
     }
+    return temp;
+}
 
+float ds18b20_convert_and_read_temp(const DS18B20_Info * ds18b20_info)
+{
+    float temp = 0.0f;
+    if (_is_init(ds18b20_info))
+    {
+        if (ds18b20_convert(ds18b20_info))
+        {
+            // wait at least maximum conversion time
+            _wait_for_conversion(ds18b20_info->resolution);
+
+            temp = ds18b20_read_temp(ds18b20_info);
+        }
+    }
     return temp;
 }
+
+

main/ds18b20.h

@@ -136,12 +136,39 @@ DS18B20_RESOLUTION ds18b20_read_resolution(DS18B20_Info * ds18b20_info);
 OneWireBus_ROMCode ds18b20_read_rom(DS18B20_Info * ds18b20_info);
 
 /**
- * @brief Get current temperature from device.
+ * @brief Start a temperature measurement conversion on a single device.
+ * @param[in] ds18b20_info Pointer to device info instance.
+ */
+bool ds18b20_convert(const DS18B20_Info * ds18b20_info);
+
+/**
+ * @brief Start temperature conversion on all connected devices.
+ * @param[in] bus Pointer to initialised bus instance.
+ */
+void ds18b20_convert_all(const OneWireBus * bus);
+
+/**
+ * @brief Wait for the maximum conversion time according to the current resolution of the device.
+ * @param[in] bus Pointer to initialised bus instance.
+ */
+void ds18b20_wait_for_conversion(const DS18B20_Info * ds18b20_info);
+
+/**
+ * @brief Read last temperature measurement from device.
+ *
+ * This is typically called after ds18b20_start_mass_conversion(), provided enough time
+ * has elapsed to ensure that all devices have completed their conversions.
  * @param[in] ds18b20_info Pointer to device info instance. Must be initialised first.
- * @return The current temperature returned by the device, in degrees Celsius.
+ * @return The measurement value returned by the device, in degrees Celsius.
  */
-float ds18b20_get_temp(const DS18B20_Info * ds18b20_info);
+float ds18b20_read_temp(const DS18B20_Info * ds18b20_info);
 
+/**
+ * @brief Convert, wait and read current temperature from device.
+ * @param[in] ds18b20_info Pointer to device info instance. Must be initialised first.
+ * @return The measurement value returned by the device, in degrees Celsius.
+ */
+float ds18b20_convert_and_read_temp(const DS18B20_Info * ds18b20_info);
 
 #ifdef __cplusplus
 }

main/ds18b20_main.c

@@ -72,6 +72,11 @@ void app_main()
         found = owb_search_next(owb, &search_state);
     }
 
+    //uint64_t rom_code = 0x0001162e87ccee28;  // pink
+    //uint64_t rom_code = 0xf402162c6149ee28;  // green
+    //uint64_t rom_code = 0x1502162ca5b2ee28;  // orange
+    //uint64_t rom_code = owb_read_rom(owb);
+
     // known ROM codes (LSB first):
     OneWireBus_ROMCode known_device = {
         .fields.family = { 0x28 },
@@ -82,15 +87,8 @@ void app_main()
     owb_string_from_rom_code(known_device, rom_code_s, sizeof(rom_code_s));
     printf("Device %s is %s\n", rom_code_s, owb_verify_rom(owb, known_device) ? "present" : "not present");
 
-    //uint64_t rom_code = 0x0001162e87ccee28;  // pink
-    //uint64_t rom_code = 0xf402162c6149ee28;  // green
-    //uint64_t rom_code = 0x1502162ca5b2ee28;  // orange
-    //uint64_t rom_code = owb_read_rom(owb);
-
     // Create a DS18B20 device on the 1-Wire bus
 #ifdef USE_STATIC
-    DS18B20_Info ds18b20_info_static;       // static allocation
-    DS18B20_Info * ds18b20_info = &ds18b20_info_static;
     DS18B20_Info devices_static[MAX_DEVICES] = {0};
     DS18B20_Info * devices[MAX_DEVICES] = {0};
     for (int i = 0; i < MAX_DEVICES; ++i)
@@ -98,7 +96,6 @@ void app_main()
         devices[i] = &(devices_static[i]);
     }
 #else
-    DS18B20_Info * ds18b20_info = ds18b20_malloc();  // heap allocation
     DS18B20_Info * devices[MAX_DEVICES] = {0};
 #endif
 
@@ -123,21 +120,44 @@ void app_main()
         ds18b20_set_resolution(ds18b20_info, DS18B20_RESOLUTION);
     }
 
-    // read temperatures from all sensors sequentially
-    while (1)
+//    // read temperatures from all sensors sequentially
+//    while (1)
+//    {
+//        printf("\nTemperature readings (degrees C):\n");
+//        for (int i = 0; i < num_devices; ++i)
+//        {
+//            float temp = ds18b20_get_temp(devices[i]);
+//            printf("  %d: %.3f\n", i, temp);
+//        }
+//        vTaskDelay(1000 / portTICK_PERIOD_MS);
+//    }
+
+    // read temperatures more efficiently by starting conversions on all devices at the same time
+    if (num_devices > 0)
     {
-        printf("\nTemperature readings (degrees C):\n");
-        for (int i = 0; i < num_devices; ++i)
+        while (1)
         {
-            float temp = ds18b20_get_temp(devices[i]);
-            printf("  %d: %.3f\n", i, temp);
+            printf("\nTemperature readings (degrees C):\n");
+            ds18b20_convert_all(owb);
+
+            // we know all devices use the same resolution, so use the first device to determine the delay
+            ds18b20_wait_for_conversion(devices[0]);
+
+            for (int i = 0; i < num_devices; ++i)
+            {
+                float temp = ds18b20_read_temp(devices[i]);
+                printf("  %d: %.3f\n", i, temp);
+            }
+            vTaskDelay(1000 / portTICK_PERIOD_MS);
         }
-        vTaskDelay(1000 / portTICK_PERIOD_MS);
     }
 
 #ifndef USE_STATIC
     // clean up dynamically allocated data
-    ds18b20_free(&ds18b20_info);
+    for (int i = 0; i < num_devices; ++i)
+    {
+        ds18b20_free(&devices[i]);
+    }
     owb_free(&owb);
 #endif
 

main/owb.h

@@ -80,6 +80,20 @@ typedef union
 
 } OneWireBus_ROMCode;
 
+/**
+ * @brief Represents the state of a device search on the 1-Wire bus.
+ *
+ *        Pass a pointer to this structure to owb_search_first() and
+ *        owb_search_next() to iterate through detected devices on the bus.
+ */
+typedef struct
+{
+    OneWireBus_ROMCode rom_code;
+    int last_discrepancy;
+    int last_family_discrepancy;
+    int last_device_flag;
+} OneWireBus_SearchState;
+
 /**
  * @brief Construct a new 1-Wire bus instance.
  *        New instance should be initialised before calling other functions.
@@ -188,23 +202,6 @@ uint8_t owb_crc8_byte(uint8_t crc, uint8_t data);
  */
 uint8_t owb_crc8_bytes(uint8_t crc, const uint8_t * data, size_t len);
 
-
-// Search API
-
-/**
- * @brief Represents the state of a device search on the 1-Wire bus.
- *
- *        Pass a pointer to this structure to owb_search_first() and
- *        owb_search_next() to iterate through detected devices on the bus.
- */
-typedef struct
-{
-    OneWireBus_ROMCode rom_code;
-    int last_discrepancy;
-    int last_family_discrepancy;
-    int last_device_flag;
-} OneWireBus_SearchState;
-
 /**
  * @brief Locates the first device on the 1-Wire bus, if present.
  * @param[in] bus Pointer to initialised bus instance.