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pimoroni-pico/drivers/sgp30/sgp30.cpp

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/******************************************************************************
sgp30.cpp
Code based on "Sensirion_Gas_Sensors_Datasheet_SGP30.pdf" on sensirion.com.
Code written by Simon Reap, March 17, 2021
https://github.com/simon3270/pico-pimoroni
This code is released under the [MIT License](http://opensource.org/licenses/MIT).
Please review the LICENSE file included with this example.
Distributed as-is; no warranty is given.
******************************************************************************/
#include "sgp30.hpp"
namespace pimoroni {
bool SGP30::init() {
i2c_init(i2c, 400000);
gpio_set_function(sda, GPIO_FUNC_I2C);
gpio_pull_up(sda);
gpio_set_function(scl, GPIO_FUNC_I2C);
gpio_pull_up(scl);
soft_reset();
if(!retrieve_unique_id()) {
return false;
}
// Retrieve and check Feature Set
uint16_t featureset;
if(!read_reg_1_word(GET_FEATURE_SET_VERSION, 10, &featureset))
return false;
if((featureset & 0xF0) != SGP30_REQ_FEATURES)
return false;
// Start the measurement process
// - parameter true = wait for readings to initialise
// false = return immediately
// As usual, function returns true if the request succeeded
// if (!start_measurement(true))
// return false;
return true;
}
i2c_inst_t* SGP30::get_i2c() const {
return i2c;
}
int SGP30::get_sda() const {
return sda;
}
int SGP30::get_scl() const {
return scl;
}
// Get the unique ID from the Chip. Will fail if no chip attached
bool SGP30::retrieve_unique_id() {
// return the Chip ID, in three separate 16-bit values
return read_reg_3_words(GET_SERIAL_ID, 10, serial_number, serial_number + 1, serial_number + 2);
}
// get the previously-retreved Chip ID as the lower 48 bits of a 64-bit uint
uint64_t SGP30::get_unique_id() {
return (((uint64_t)serial_number[0]) << 32) \
+ (((uint64_t)serial_number[1]) << 16) \
+ serial_number[2];
}
// Write a soft reset - writes globally, so all devices on this
// I2C bus receive the request
bool SGP30::soft_reset() {
return write_global(SOFT_RESET, 10);
}
// Start the measurement process.
// If the parameter is true, wait for the readings to be valid
// If false, return immediately
bool SGP30::start_measurement(bool wait_for_setup) {
// First kick off the "measurement" phase
bool rc = write_reg(INIT_AIR_QUALITY, 10);
// Optionally wait up to 20 seconds for the measurement process to initiate
if(wait_for_setup) {
// It takes 15 seconds to start the measurement process but allow 20.
// Ignore the first 2 readings completely.
uint16_t eCO2, TVOC;
uint8_t sec_count = 0;
while(sec_count < 20) {
sleep_ms(988); // Will sleep last 12ms of 1sec in get_air_quality()
get_air_quality(&eCO2, &TVOC);
if((sec_count >= 2) && (eCO2 != 400 || TVOC != 0)) {
// startup process finished
break;
}
sec_count++;
}
}
return rc;
}
// get the air quality values - will be 400 and 0 respectively for the
// first 15 seconds after starting measurement
bool SGP30::get_air_quality(uint16_t * eCO2, uint16_t * TVOC) {
return read_reg_2_words(MEASURE_AIR_QUALITY, 12, eCO2, TVOC);
}
// Get the raw readings - not useful in real-world settings
bool SGP30::get_air_quality_raw(uint16_t * rawH2, uint16_t * rawEthanol) {
return read_reg_2_words(MEASURE_RAW_SIGNALS, 25, rawH2, rawEthanol);
}
// Get the baseline compensation values for eCO2 and VOC
bool SGP30::get_baseline(uint16_t *eco2, uint16_t *tvoc) {
return read_reg_2_words(GET_BASELINE, 10, eco2, tvoc);
}
// Write the baseline compensation values for eCO2 and VOC
void SGP30::set_baseline(uint16_t eco2, uint16_t tvoc) {
write_reg_2_words(SET_BASELINE, 10, eco2, tvoc);
}
// Set the absolute humidity, e.g. from an SHTxx chip
bool SGP30::set_humidity(uint32_t absolute_humidity) {
if(absolute_humidity > 256000) {
return false;
}
uint16_t ah_scaled = (uint16_t)(((uint64_t)absolute_humidity * 256 * 16777) >> 24);
return write_reg_1_word(SET_HUMIDITY, 10, ah_scaled);
}
// Write a single byte globally (not to a specifc I2c address)
bool SGP30::write_global(uint16_t reg, uint16_t delay_ms) {
uint8_t buffer[1] = { (uint8_t)(reg & 0xFF)};
i2c_write_blocking(i2c, 0, buffer, 1, false);
sleep_ms(delay_ms);
return true;
}
// Write just the register to the i2c address, no parameter
bool SGP30::write_reg(uint16_t reg, uint16_t delay_ms) {
uint8_t buffer[2] = { (uint8_t)((reg >> 8) & 0xFF), (uint8_t)(reg & 0xFF)};
i2c_write_blocking(i2c, address, buffer, 2, false);
sleep_ms(delay_ms);
return true;
}
// Write one 16-bit word (+CRC)
bool SGP30::write_reg_1_word(uint16_t reg, uint16_t delay_ms, uint16_t value) {
uint8_t buffer[5] = { (uint8_t)((reg >> 8) & 0xFF), (uint8_t)(reg & 0xFF),
(uint8_t)((value >> 8) & 0xFF), (uint8_t)(value & 0xFF), calculate_crc(value)};
i2c_write_blocking(i2c, address, buffer, 5, false);
sleep_ms(delay_ms);
return true;
}
// Write two 16-bit words (+CRC)
bool SGP30::write_reg_2_words(uint16_t reg, uint16_t delay_ms, uint16_t value1, uint16_t value2) {
uint8_t buffer[8] = { (uint8_t)((reg >> 8) & 0xFF), (uint8_t)(reg & 0xFF),
(uint8_t)((value1 >> 8) & 0xFF), (uint8_t)(value1 & 0xFF), calculate_crc(value1),
(uint8_t)((value2 >> 8) & 0xFF), (uint8_t)(value2 & 0xFF), calculate_crc(value2)};
i2c_write_blocking(i2c, address, buffer, 8, false);
sleep_ms(delay_ms);
return true;
}
// Write register and read one 16-bit word in response
bool SGP30::read_reg_1_word(uint16_t reg, uint16_t delay_ms, uint16_t *value) {
uint8_t regbuf[2] = { (uint8_t)((reg >> 8) & 0xFF), (uint8_t)(reg & 0xFF) };
uint8_t buffer[3];
i2c_write_blocking(i2c, address, regbuf, 2, true);
sleep_ms(delay_ms);
i2c_read_blocking(i2c, address, buffer, 3, false);
if(buffer[2] != calculate_crc(buffer[0], buffer[1]))
return false;
*value = (buffer[0] << 8) + buffer[1];
return true;
}
// Write register and read two 16-bit words
bool SGP30::read_reg_2_words(uint16_t reg, uint16_t delay_ms, uint16_t *value1, uint16_t *value2) {
uint8_t regbuf[2] = { (uint8_t)((reg >> 8) & 0xFF), (uint8_t)(reg & 0xFF) };
uint8_t buffer[6];
i2c_write_blocking(i2c, address, regbuf, 2, true);
sleep_ms(delay_ms);
i2c_read_blocking(i2c, address, buffer, 6, false);
if((buffer[2] != calculate_crc(buffer[0], buffer[1])) || (buffer[5] != calculate_crc(buffer[3], buffer[4]))) {
return false;
}
*value1 = (buffer[0] << 8) + buffer[1];
*value2 = (buffer[3] << 8) + buffer[4];
return true;
}
// Write register and read three 16-bit words
bool SGP30::read_reg_3_words(uint16_t reg, uint16_t delay_ms, uint16_t *value1, uint16_t *value2, uint16_t *value3) {
uint8_t regbuf[2] = { (uint8_t)((reg >> 8) & 0xFF), (uint8_t)(reg & 0xFF) };
uint8_t buffer[9];
i2c_write_blocking(i2c, address, regbuf, 2, true);
sleep_ms(delay_ms);
i2c_read_blocking(i2c, address, buffer, 9, false);
if(buffer[2] != calculate_crc(buffer[0], buffer[1])) {
return false;
}
if (buffer[5] != calculate_crc(buffer[3], buffer[4])) {
return false;
}
if (buffer[8] != calculate_crc(buffer[6], buffer[7])) {
return false;
}
*value1 = (buffer[0] << 8) + buffer[1];
*value2 = (buffer[3] << 8) + buffer[4];
*value3 = (buffer[6] << 8) + buffer[7];
return true;
}
// calculate the CRC for a single 16-bit word
uint8_t SGP30::calculate_crc(uint16_t value) {
return calculate_crc((value >> 8) && 0xFF, value & 0xFF);
}
// calculate the CRC for two 8-bit bytes
uint8_t SGP30::calculate_crc(uint8_t value1, uint8_t value2) {
// calculates 8-Bit checksum with given polynomial
uint8_t crc = SGP30_CRC_BASE;
crc ^= value1;
for(uint8_t b = 0; b < 8; b++) {
if(crc & 0x80)
crc = (crc << 1) ^ SGP30_CRC_SEED;
else
crc <<= 1;
}
crc ^= value2;
for(uint8_t b = 0; b < 8; b++) {
if(crc & 0x80)
crc = (crc << 1) ^ SGP30_CRC_SEED;
else
crc <<= 1;
}
return crc;
}
}
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