SHT3x driver - some minor changes

- lookup tables made const to be held in flash
- crc8 computation changed to a non table lookup version
- measurement duration is now given in ticks and can be used directly
  for vTaskDelay (documentation and examples changed accordingly)

examples/sht3x/sht3x_one_sensor/sht3x_one_sensor.c

@@ -17,7 +17,7 @@
  *   +------------------------+     +----------+
  */
 
-// #define SINGLE_SHOT_MODE
+#define SINGLE_SHOT_MODE
  
 #include "espressif/esp_common.h"
 #include "esp/uart.h"
@@ -55,7 +55,7 @@ void user_task (void *pvParameters)
         
         // passive waiting until measurement results are available
         if (duration > 0)
-            vTaskDelay (duration/portTICK_PERIOD_MS);
+            vTaskDelay (duration);
         
         // retrieve the values and do something with them
         if (sht3x_get_results (sensor, &values))

examples/sht3x/sht3x_two_sensors/sht3x_two_sensors.c

@@ -18,7 +18,7 @@
  *   |          GPIO 12 (SDA) ------- SDA      |
  *   +------------------------+     +----------+
  */
- 
+
 #include "espressif/esp_common.h"
 #include "esp/uart.h"
 
@@ -61,7 +61,7 @@ void user_task_sensor1 (void *pvParameters)
 
         // passive waiting until measurement results are available
         if (duration > 0)
-            vTaskDelay (duration/portTICK_PERIOD_MS);
+            vTaskDelay (duration);
         
         // retrieve the values and do something with them
         if (sht3x_get_results (sensor1, &values))

extras/sht3x/README.md

@@ -119,7 +119,7 @@ void user_task (void *pvParameters)
 
     // passive waiting until first measurement results are available
     if (duration > 0)
-        vTaskDelay (duration/portTICK_PERIOD_MS);
+        vTaskDelay (duration);
 
     // busy waiting until first measurement results are available
     // while (sht3x_is_measuring (sensor) > 0) ;
@@ -140,7 +140,7 @@ void user_task (void *pvParameters)
 }
 ```
 
-At the beginning of the task, the periodic measurement is started by function **_sht3x_start_measurement_** with a rate of 1 measurement per second. Using the measurement duration returned from this function, the task is delayed using **_vTaskDelay_** to wait for first measurement results. The busy waiting alternative using function **_sht3x_is_measuring_** is shown in comments. Inside the task loop, the measurement results are fetched periodically using function **_sht3x_get_results_** with a rate of once per second.
+At the beginning of the task, the periodic measurement is started by function **_sht3x_start_measurement_** with a rate of 1 measurement per second. Using the measurement duration in RTOS ticks returned from this function, the task is delayed using **_vTaskDelay_** to wait for first measurement results. The busy waiting alternative using function **_sht3x_is_measuring_** is shown in comments. Inside the task loop, the measurement results are fetched periodically using function **_sht3x_get_results_** with a rate of once per second.
 
 In the **single shot mode**, the measurement has to be triggered 
 in each cycle. Waiting for measurement results is also required in each cylce, before the results can be fetched.
@@ -162,7 +162,7 @@ void user_task (void *pvParameters)
         
         // passive waiting until measurement results are available
         if (duration > 0)
-            vTaskDelay (duration/portTICK_PERIOD_MS);
+            vTaskDelay (duration);
         
         // busy waiting until first measurement results are available
         // while (sht3x_is_measuring (sensor) > 0) ;
@@ -233,7 +233,7 @@ static sht3x_sensor_t* sensor;    // sensor device data structure
 /*
  * User task that fetches latest measurement results of sensor every 2
  * seconds. It starts the SHT3x in periodic mode with 1 measurements per
- * second (*periodic_1mps*). It uses busy waiting for first measurement
+ * second (*periodic_1mps*). It uses passive waiting for first measurement
  * results.
  */
 void user_task (void *pvParameters)
@@ -242,9 +242,10 @@ void user_task (void *pvParameters)
 
     // start periodic measurements with 1 measurement per second
     sht3x_start_measurement (sensor, periodic_1mps);
-
+    
+    // passive waiting until measurement results are available
     if (duration > 0)
-        vTaskDelay (duration/portTICK_PERIOD_MS);
+        vTaskDelay (duration);
 
     TickType_t last_wakeup = xTaskGetTickCount();
     

extras/sht3x/sht3x.c

@@ -61,14 +61,14 @@
 #define SHT3x_FETCH_DATA_CMD           0xE000
 #define SHT3x_HEATER_OFF_CMD           0x3066
 
-uint16_t SHT3x_MEASURE_CMD[6][3] = { {0x2c06,0x2c0d,0x2c10},    // [SINGLE_SHOT][H,M,L]
+const uint16_t SHT3x_MEASURE_CMD[6][3] = { {0x2c06,0x2c0d,0x2c10},    // [SINGLE_SHOT][H,M,L]
-                                     {0x2032,0x2024,0x202f},    // [PERIODIC_05][H,M,L]
+                                           {0x2032,0x2024,0x202f},    // [PERIODIC_05][H,M,L]
-                                     {0x2130,0x2126,0x212d},    // [PERIODIC_05][H,M,L]
+                                           {0x2130,0x2126,0x212d},    // [PERIODIC_05][H,M,L]
-                                     {0x2236,0x2220,0x222b},    // [PERIODIC_05][H,M,L]
+                                           {0x2236,0x2220,0x222b},    // [PERIODIC_05][H,M,L]
-                                     {0x2234,0x2322,0x2329},    // [PERIODIC_05][H,M,L]
+                                           {0x2234,0x2322,0x2329},    // [PERIODIC_05][H,M,L]
-                                     {0x2737,0x2721,0x272a} };  // [PERIODIC_05][H,M,L]
+                                           {0x2737,0x2721,0x272a} };  // [PERIODIC_05][H,M,L]
                                      
-int32_t SHT3x_MEASURE_DURATION[3] = {30,20,20};  // [High, Medium, Low]
+const int32_t SHT3x_MEASURE_DURATION[3] = {3,2,2};  // tick counts [High, Medium, Low]
 
 #ifdef SHT3x_DEBUG
 #define debug(s, f, ...) printf("%s %s: " s "\n", "SHT3x", f, ## __VA_ARGS__)
@@ -111,7 +111,7 @@ sht3x_sensor_t* sht3x_init_sensor(uint8_t bus, uint8_t addr)
     dev->mode = single_shot;
     dev->repeatability = high;
     dev->meas_started = false;
-    dev->meas_start_time = 0;
+    dev->meas_start_tick = 0;
     
     dev->active = true;
 
@@ -149,10 +149,10 @@ int32_t sht3x_start_measurement (sht3x_sensor_t* dev, sht3x_mode_t mode)
     // start measurement according to selected mode and return an duration estimate
     if (sht3x_send_command(dev, SHT3x_MEASURE_CMD[dev->mode][dev->repeatability]))
     {
-        dev->meas_start_time = sdk_system_get_time ();
+        dev->meas_start_tick = xTaskGetTickCount ();
         dev->meas_started = true;
         dev->meas_first = true;
-        return SHT3x_MEASURE_DURATION[dev->repeatability];   // in ms
+        return SHT3x_MEASURE_DURATION[dev->repeatability];   // in RTOS ticks
     }
 
     dev->error_code |= SHT3x_SEND_MEAS_CMD_FAILED;
@@ -181,7 +181,7 @@ int32_t sht3x_is_measuring (sht3x_sensor_t* dev)
         
     uint32_t elapsed_time;
 
-    elapsed_time = (sdk_system_get_time() - dev->meas_start_time) / 1000;  // in ms
+    elapsed_time = (xTaskGetTickCount() - dev->meas_start_tick);  // in RTOS ticks
 
     if (elapsed_time >= SHT3x_MEASURE_DURATION[dev->repeatability])
         return 0;
@@ -371,46 +371,24 @@ static bool sht3x_get_status (sht3x_sensor_t* dev, uint16_t* status)
 }
 
 
-
+const uint8_t g_polynom = 0x31;
-static uint8_t crc8_table[256];         // lookup table with precomputed crc values
-static bool crc8_first_time = true;     // indicator whether table has still to be created
-
-static void generate_crc8_table()
-{
-    const uint8_t g_polynom = 0x31;
-
-    for (int i=0; i < 256; i++)
-    {
-        uint8_t value = (uint8_t)i;
-        for (uint8_t bit = 0; bit < 8; bit++)
-        {
-            bool xor = value & 0x80;
-            value = value << 1;
-            value = xor ? value ^ g_polynom : value;
-        }
-        crc8_table[i] = value;
-    }
-} 
-
 
 static uint8_t crc8 (uint8_t data[], int len)
 {
-    // generate crc lookup table first time it is called
-    if (crc8_first_time)
-    {
-        crc8_first_time = false;
-        generate_crc8_table ();
-    }
-
     // initialization value
     uint8_t crc = 0xff;
     
     // iterate over all bytes
     for (int i=0; i < len; i++)
     {
-        uint8_t b = data[i];
+        crc ^= data[i];  
-        uint8_t data = (uint8_t)(b ^ crc);
+    
-        crc = (uint8_t)(crc8_table[data]);
+        for (int i = 0; i < 8; i++)
+        {
+            bool xor = crc & 0x80;
+            crc = crc << 1;
+            crc = xor ? crc ^ g_polynom : crc;
+        }
     }
 
     return crc;

extras/sht3x/sht3x.h

@@ -137,7 +137,7 @@ typedef struct {
     sht3x_repeat_t  repeatability;   // used repeatability
  
     bool            meas_started;    // indicates whether measurement started
-    uint32_t        meas_start_time; // measurement start time in microseconds
+    TickType_t      meas_start_tick; // measurement start time in RTOS ticks
     bool            meas_first;      // first measurement in periodic mode
     
 } sht3x_sensor_t;    
@@ -161,28 +161,31 @@ sht3x_sensor_t* sht3x_init_sensor (uint8_t bus, uint8_t addr);
  * @brief	Start single shot or periodic measurements
  *
  * The function starts the measurement either in *single shot mode* 
- * (exactly one measurement) or *periodic mode* (periodic measurements). 
+ * (exactly one measurement) or *periodic mode* (periodic measurements) and
+ * returns an estimated measurement duration given in RTOS ticks. 
  *
  * In the *single shot mode*, this function has to be called for each
  * measurement. The measurement duration returned by the function has to be
  * waited every time before the results can be fetched. 
  *
- * In the *periodic mode*, this function has to be called only once. Also the
+ * In the *periodic mode*, this function has to be called only once. Also 
- * measurement duration must be waited only once until the first results are
+ * the measurement duration must be waited only once until the first
- * available. After this first measurement, the sensor then automatically 
+ * results are available. After this first measurement, the sensor then
- * performs all subsequent measurements. The rate of periodic measurements can
+ * automatically performs all subsequent measurements. The rate of periodic
- * be 10, 4, 2, 1 or 0.5 measurements per second (mps). The user task can 
+ * measurements can be 10, 4, 2, 1 or 0.5 measurements per second (mps). Due
- * fetch the results with the half or less rate. The rate of the periodic 
+ * to inaccuracies in timing of the sensor, the user task should fetch the
- * measurements is defined by the parameter *mode*.
+ * results at a lower rate. The rate of the periodic measurements is defined
+ * by the parameter *mode*.
  *
- * On success, the function returns an estimated measurement duration. This 
+ * On success, the function returns an estimated measurement duration given
- * defines the duration needed by the sensor before first results become 
+ * in RTOS ticks. This defines the duration needed by the sensor before
- * available. The user task has to wait this time before it can fetch the 
+ * first results become available. The user task has to wait this time
- * results using function *sht3x_get_results* or *sht3x_get_raw_data*.
+ * before it can fetch the results using function *sht3x_get_results* or
+ * *sht3x_get_raw_data*.
  *
- * @param   dev       pointer to sensor device data structure
+ * @param   dev   pointer to sensor device data structure
- * @param   mode      measurement mode, see type *sht3x_mode_t*
+ * @param   mode  measurement mode, see type *sht3x_mode_t*
- * @return            true on success, false on error
+ * @return        measurement duration in RTOS ticks or -1 on error
  */
 int32_t sht3x_start_measurement (sht3x_sensor_t* dev, sht3x_mode_t mode);
 
@@ -190,9 +193,9 @@ int32_t sht3x_start_measurement (sht3x_sensor_t* dev, sht3x_mode_t mode);
 /**
  * @brief	Check whether measurement is still running
  *
- * The function can be used to test whether a measurement has been started
+ * The function can be used to test whether a measurement has been
- * at all and how long it still takes before measurement results become
+ * started and how long it still takes before measurement results
- * available. The return value can be
+ * become available. The return value is given in RTOS ticks and can be
  *
  *   >0  in case the measurement is is still running,
  *    0  in case the measurement has been already finished, or
@@ -201,8 +204,8 @@ int32_t sht3x_start_measurement (sht3x_sensor_t* dev, sht3x_mode_t mode);
  * That is, a return value greater than 0 indicates that the measurement
  * results are still not available and the user task has to wait that time.
  * 
- * @param   dev       pointer to sensor device data structure
+ * @param   dev   pointer to sensor device data structure
- * @return            remaining measurement duration or -1 on error
+ * @return        remaining measurement duration in RTOS ticks or -1 on error
  */
 int32_t sht3x_is_measuring (sht3x_sensor_t* dev);