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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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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;