Implement solo device optimisations - if there is only one device on the bus, addressing can be simplified.

README.md

@@ -8,11 +8,15 @@ It supports multiple devices on the same 1-Wire bus.
 
 It is written and tested for the [ESP-IDF](https://github.com/espressif/esp-idf) environment, using the xtensa-esp32-elf toolchain (gcc version 5.2.0).
 
-## Supported Features
+## Features
+
+This library includes:
 
  * External power supply mode (parasitic mode not yet supported).
  * Static (stack-based) or dynamic (malloc-based) memory model.
+ * No globals - support any number of 1-Wire buses simultaneously.
  * 1-Wire device detection and validation, including search for multiple devices on a single bus.
+ * Addressing optimisation for a single (solo) device on a bus.
  * 1-Wire bus operations including multi-byte read and write operations.
  * CRC checks on ROM code and temperature data.
  * Programmable temperature measurement resolution (9, 10, 11 or 12-bit resolution).
@@ -47,9 +51,8 @@ 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.
+ * Simultaneous temperature conversion from multiple devices on the same bus - concurrency.
  * Alarm support.
  * EEPROM support.
- * Single device optimisations - avoid ROM addressing when only one device exists.
  * Parasitic power support.
-
+ * FreeRTOS event-based example.

main/ds18b20.c

@@ -92,6 +92,36 @@ static bool _is_init(const DS18B20_Info * ds18b20_info)
     return ok;
 }
 
+static bool _address_device(const DS18B20_Info * ds18b20_info)
+{
+    bool present = false;
+    if (_is_init(ds18b20_info))
+    {
+        present = owb_reset(ds18b20_info->bus);
+        if (present)
+        {
+            if (ds18b20_info->solo)
+            {
+                // if there's only one device on the bus, we can skip
+                // sending the ROM code and instruct it directly
+                owb_write_byte(ds18b20_info->bus, OWB_ROM_SKIP);
+            }
+            else
+            {
+                // if there are multiple devices on the bus, a Match ROM command
+                // must be issued to address a specific slave
+                owb_write_byte(ds18b20_info->bus, OWB_ROM_MATCH);
+                owb_write_rom_code(ds18b20_info->bus, ds18b20_info->rom_code);
+            }
+        }
+        else
+        {
+            ESP_LOGE(TAG, "ds18b20 device not responding");
+        }
+    }
+    return present;
+}
+
 static bool _check_resolution(DS18B20_RESOLUTION resolution)
 {
     return (resolution >= DS18B20_RESOLUTION_9_BIT) && (resolution <= DS18B20_RESOLUTION_12_BIT);
@@ -125,12 +155,12 @@ static Scratchpad _read_scratchpad(const DS18B20_Info * ds18b20_info, size_t cou
     count = _min(sizeof(Scratchpad), count);   // avoid overflow
     Scratchpad scratchpad = {0};
     ESP_LOGD(TAG, "scratchpad read %d bytes: ", count);
-    owb_reset(ds18b20_info->bus);
-    owb_write_byte(ds18b20_info->bus, OWB_ROM_MATCH);
-    owb_write_rom_code(ds18b20_info->bus, ds18b20_info->rom_code);
+    if (_address_device(ds18b20_info))
+    {
         owb_write_byte(ds18b20_info->bus, DS18B20_FUNCTION_SCRATCHPAD_READ);
         owb_read_bytes(ds18b20_info->bus, (uint8_t *)&scratchpad, count);
         esp_log_buffer_hex(TAG, &scratchpad, count);
+    }
     return scratchpad;
 }
 
@@ -141,9 +171,8 @@ static bool _write_scratchpad(const DS18B20_Info * ds18b20_info, const Scratchpa
     // All three bytes MUST be written before the next reset to avoid corruption.
     if (_is_init(ds18b20_info))
     {
-        owb_reset(ds18b20_info->bus);
-        owb_write_byte(ds18b20_info->bus, OWB_ROM_MATCH);
-        owb_write_rom_code(ds18b20_info->bus, ds18b20_info->rom_code);
+        if (_address_device(ds18b20_info))
+        {
             owb_write_byte(ds18b20_info->bus, DS18B20_FUNCTION_SCRATCHPAD_WRITE);
             owb_write_bytes(ds18b20_info->bus, (uint8_t *)&scratchpad->trigger_high, 3);
             ESP_LOGD(TAG, "scratchpad write 3 bytes:");
@@ -164,6 +193,7 @@ static bool _write_scratchpad(const DS18B20_Info * ds18b20_info, const Scratchpa
                 }
             }
         }
+    }
     return result;
 }
 
@@ -193,15 +223,45 @@ void ds18b20_free(DS18B20_Info ** ds18b20_info)
     }
 }
 
-void ds18b20_init(DS18B20_Info * ds18b20_info, OneWireBus * bus, OneWireBus_ROMCode rom_code)
+static void _init(DS18B20_Info * ds18b20_info, OneWireBus * bus)
 {
     if (ds18b20_info != NULL)
     {
         ds18b20_info->bus = bus;
-        ds18b20_info->rom_code = rom_code;
+        memset(&ds18b20_info->rom_code, 0, sizeof(ds18b20_info->rom_code));
         ds18b20_info->use_crc = false;
         ds18b20_info->resolution = DS18B20_RESOLUTION_INVALID;
+        ds18b20_info->solo = false;   // assume multiple devices unless told otherwise
         ds18b20_info->init = true;
+    }
+    else
+    {
+        ESP_LOGE(TAG, "ds18b20_info is NULL");
+    }
+}
+
+void ds18b20_init(DS18B20_Info * ds18b20_info, OneWireBus * bus, OneWireBus_ROMCode rom_code)
+{
+    if (ds18b20_info != NULL)
+    {
+        _init(ds18b20_info, bus);
+        ds18b20_info->rom_code = rom_code;
+
+        // read current resolution from device as it may not be power-on or factory default
+        ds18b20_info->resolution = ds18b20_read_resolution(ds18b20_info);
+    }
+    else
+    {
+        ESP_LOGE(TAG, "ds18b20_info is NULL");
+    }
+}
+
+void ds18b20_init_solo(DS18B20_Info * ds18b20_info, OneWireBus * bus)
+{
+    if (ds18b20_info != NULL)
+    {
+        _init(ds18b20_info, bus);
+        ds18b20_info->solo = true;
 
         // read current resolution from device as it may not be power-on or factory default
         ds18b20_info->resolution = ds18b20_read_resolution(ds18b20_info);
@@ -297,26 +357,22 @@ static void _wait_for_conversion(DS18B20_RESOLUTION resolution)
     }
 }
 
-float ds18b20_get_temp(DS18B20_Info * ds18b20_info)
+float ds18b20_get_temp(const DS18B20_Info * ds18b20_info)
 {
     float temp = 0.0f;
     if (_is_init(ds18b20_info))
     {
         OneWireBus * bus = ds18b20_info->bus;
-        if (owb_reset(bus))
+        if (_address_device(ds18b20_info))
         {
-            //owb_write_byte(bus, OWB_ROM_SKIP);
-            owb_write_byte(bus, OWB_ROM_MATCH);
-            owb_write_rom_code(bus, ds18b20_info->rom_code);
+            // initiate a temperature measurement
             owb_write_byte(bus, DS18B20_FUNCTION_TEMP_CONVERT);
 
+            // wait at least maximum conversion time
             _wait_for_conversion(ds18b20_info->resolution);
 
-            // reset
-            owb_reset(bus);
-            //owb_write_byte(bus, OWB_ROM_SKIP);
-            owb_write_byte(bus, OWB_ROM_MATCH);
-            owb_write_rom_code(bus, ds18b20_info->rom_code);
+            // read measurement
+            _address_device(ds18b20_info);
             owb_write_byte(bus, DS18B20_FUNCTION_SCRATCHPAD_READ);
 
             uint8_t temp_LSB = 0;

main/ds18b20.h

@@ -59,6 +59,7 @@ typedef enum
 typedef struct
 {
     bool init;                     ///< True if struct has been initialised, otherwise false
+    bool solo;                     ///< True if device is intended to be the only one connected to the bus, 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_ROMCode rom_code;   ///< The ROM code used to address this device on the bus
@@ -87,6 +88,20 @@ void ds18b20_free(DS18B20_Info ** ds18b20_info);
  */
 void ds18b20_init(DS18B20_Info * ds18b20_info, OneWireBus * bus, OneWireBus_ROMCode rom_code);
 
+/**
+ * @brief Initialise a device info instance with the specified GPIO as a solo device on the bus.
+ *
+ * This is subject to the requirement that this device is the ONLY device on the bus.
+ * This allows for faster commands to be used without ROM code addressing.
+ *
+ * NOTE: if additional devices are added to the bus, operation will cease to work correctly.
+ *
+ * @param[in] ds18b20_info Pointer to device info instance.
+ * @param[in] bus Pointer to initialised 1-Wire bus instance.
+ * @param[in] rom_code Device-specific ROM code to identify a device on the bus.
+ */
+void ds18b20_init_solo(DS18B20_Info * ds18b20_info, OneWireBus * bus);
+
 /**
  * @brief Enable or disable use of CRC checks on device communications.
  * @param[in] ds18b20_info Pointer to device info instance.
@@ -125,7 +140,7 @@ OneWireBus_ROMCode ds18b20_read_rom(DS18B20_Info * ds18b20_info);
  * @param[in] ds18b20_info Pointer to device info instance. Must be initialised first.
  * @return The current temperature returned by the device, in degrees Celsius.
  */
-float ds18b20_get_temp(DS18B20_Info * ds18b20_info);
+float ds18b20_get_temp(const DS18B20_Info * ds18b20_info);
 
 
 #ifdef __cplusplus

main/ds18b20_main.c

@@ -36,8 +36,9 @@
 #include "ds18b20.h"
 
 
-#define GPIO_DS18B20_0 (GPIO_NUM_4)
+#define GPIO_DS18B20_0       (GPIO_NUM_5)
 #define MAX_DEVICES          (8)
+#define DS18B20_RESOLUTION   (DS18B20_RESOLUTION_12_BIT)
 
 
 void app_main()
@@ -109,16 +110,20 @@ void app_main()
         DS18B20_Info * ds18b20_info = ds18b20_malloc();  // heap allocation
         devices[i] = ds18b20_info;
 #endif
+        if (num_devices == 1)
+        {
+            printf("Single device optimisations enabled\n");
+            ds18b20_init_solo(ds18b20_info, owb);          // only one device on bus
+        }
+        else
+        {
             ds18b20_init(ds18b20_info, owb, device_rom_codes[i]); // associate with bus and device
-        //ds18b20_init_solo(ds18b20_info, owb);          // only one device on bus
+        }
         ds18b20_use_crc(ds18b20_info, true);           // enable CRC check for temperature readings
-//        ds18b20_set_resolution(ds18b20_info, DS18B20_RESOLUTION_9_BIT);
-//        ds18b20_set_resolution(ds18b20_info, DS18B20_RESOLUTION_10_BIT);
-//        ds18b20_set_resolution(ds18b20_info, DS18B20_RESOLUTION_11_BIT);
-        ds18b20_set_resolution(ds18b20_info, DS18B20_RESOLUTION_12_BIT);
+        ds18b20_set_resolution(ds18b20_info, DS18B20_RESOLUTION);
     }
 
-    // read temperatures from all sensors
+    // read temperatures from all sensors sequentially
     while (1)
     {
         printf("\nTemperature readings (degrees C):\n");