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SHT3x driver - some minor changes

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- 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)
This commit is contained in:
Gunar Schorcht 2017-10-13 17:43:43 +02:00
parent 5a0fc09989
commit 1525f61fe3
5 changed files with 55 additions and 73 deletions
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4
examples/sht3x/sht3x_one_sensor/sht3x_one_sensor.c
View file

@ -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))

2
examples/sht3x/sht3x_two_sensors/sht3x_two_sensors.c
View file

@ -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))

11
extras/sht3x/README.md
View file

@ -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)
@ -243,8 +243,9 @@ 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();

62
extras/sht3x/sht3x.c
View file

@ -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]
{0x2032,0x2024,0x202f}, // [PERIODIC_05][H,M,L]
{0x2130,0x2126,0x212d}, // [PERIODIC_05][H,M,L]
{0x2236,0x2220,0x222b}, // [PERIODIC_05][H,M,L]
{0x2234,0x2322,0x2329}, // [PERIODIC_05][H,M,L]
{0x2737,0x2721,0x272a} }; // [PERIODIC_05][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]
{0x2130,0x2126,0x212d}, // [PERIODIC_05][H,M,L]
{0x2236,0x2220,0x222b}, // [PERIODIC_05][H,M,L]
{0x2234,0x2322,0x2329}, // [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)
}
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;
}
}
const uint8_t g_polynom = 0x31;
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];
uint8_t data = (uint8_t)(b ^ crc);
crc = (uint8_t)(crc8_table[data]);
crc ^= data[i];
for (int i = 0; i < 8; i++)
{
bool xor = crc & 0x80;
crc = crc << 1;
crc = xor ? crc ^ g_polynom : crc;
}
}
return crc;

45
extras/sht3x/sht3x.h
View file

@ -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
* measurement duration must be waited only once until the first results are
* available. After this first measurement, the sensor then automatically
* performs all subsequent measurements. The rate of periodic measurements can
* be 10, 4, 2, 1 or 0.5 measurements per second (mps). The user task can
* fetch the results with the half or less rate. The rate of the periodic
* measurements is defined by the parameter *mode*.
* In the *periodic mode*, this function has to be called only once. Also
* the measurement duration must be waited only once until the first
* results are available. After this first measurement, the sensor then
* automatically performs all subsequent measurements. The rate of periodic
* measurements can be 10, 4, 2, 1 or 0.5 measurements per second (mps). Due
* to inaccuracies in timing of the sensor, the user task should fetch the
* 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
* defines the duration needed by the sensor before first results become
* available. The user task has to wait this time before it can fetch the
* results using function *sht3x_get_results* or *sht3x_get_raw_data*.
* On success, the function returns an estimated measurement duration given
* in RTOS ticks. This defines the duration needed by the sensor before
* first results become available. The user task has to wait this time
* 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 mode measurement mode, see type *sht3x_mode_t*
* @return true on success, false on error
* @param dev pointer to sensor device data structure
* @param mode measurement mode, see type *sht3x_mode_t*
* @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
* at all and how long it still takes before measurement results become
* available. The return value can be
* The function can be used to test whether a measurement has been
* started and how long it still takes before measurement results
* 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
* @return remaining measurement duration or -1 on error
* @param dev pointer to sensor device data structure
* @return remaining measurement duration in RTOS ticks or -1 on error
*/
int32_t sht3x_is_measuring (sht3x_sensor_t* dev);