Method readWords

lib/i2cdev/I2Cdev.cpp:326–463

Read multiple words from a 16-bit device register. * @param devAddr I2C slave device address * @param regAddr First register regAddr to read from * @param length Number of words to read * @param data Buffer to store read data in * @param timeout Optional read timeout in milliseconds (0 to disable, leave off to use default class value in I2Cdev::readTimeout) * @return Number of words read (-1

 * @return Number of words read (-1 indicates failure)
 */
int8_t I2Cdev::readWords(uint8_t devAddr, uint8_t regAddr, uint8_t length, uint16_t *data, uint16_t timeout, void *wireObj) {
    #ifdef I2CDEV_SERIAL_DEBUG
        Serial.print("I2C (0x");
        Serial.print(devAddr, HEX);
        Serial.print(") reading ");
        Serial.print(length, DEC);
        Serial.print(" words from 0x");
        Serial.print(regAddr, HEX);
        Serial.print("...");
    #endif

    int8_t count = 0;
    uint32_t t1 = millis();

#if I2CDEV_IMPLEMENTATION == I2CDEV_ARDUINO_WIRE || I2CDEV_IMPLEMENTATION == I2CDEV_BUILTIN_SBWIRE || I2CDEV_IMPLEMENTATION == I2CDEV_TEENSY_3X_WIRE
        TwoWire *useWire = &Wire;
        if (wireObj) useWire = (TwoWire *)wireObj;

        #if (ARDUINO < 100)
            // Arduino v00xx (before v1.0), Wire library

            // I2C/TWI subsystem uses internal buffer that breaks with large data requests
            // so if user requests more than I2CDEVLIB_WIRE_BUFFER_LENGTH bytes, we have to do it in
            // smaller chunks instead of all at once
            for (uint8_t k = 0; k < length * 2; k += min(length * 2, I2CDEVLIB_WIRE_BUFFER_LENGTH)) {
                useWire->beginTransmission(devAddr);
                useWire->send(regAddr);
                useWire->endTransmission();
                useWire->beginTransmission(devAddr);
                useWire->requestFrom(devAddr, (uint8_t)(length * 2)); // length=words, this wants bytes
    
                bool msb = true; // starts with MSB, then LSB
                for (; useWire->available() && count < length && (timeout == 0 || millis() - t1 < timeout);) {
                    if (msb) {
                        // first byte is bits 15-8 (MSb=15)
                        data[count] = useWire->receive() << 8;
                    } else {
                        // second byte is bits 7-0 (LSb=0)
                        data[count] |= useWire->receive();
                        #ifdef I2CDEV_SERIAL_DEBUG
                            Serial.print(data[count], HEX);
                            if (count + 1 < length) Serial.print(" ");
                        #endif
                        count++;
                    }
                    msb = !msb;
                }
            }
        #elif (ARDUINO == 100)
            // Arduino v1.0.0, Wire library
            // Adds standardized write() and read() stream methods instead of send() and receive()
    
            // I2C/TWI subsystem uses internal buffer that breaks with large data requests
            // so if user requests more than I2CDEVLIB_WIRE_BUFFER_LENGTH bytes, we have to do it in
            // smaller chunks instead of all at once
            for (uint8_t k = 0; k < length * 2; k += min(length * 2, I2CDEVLIB_WIRE_BUFFER_LENGTH)) {
                useWire->beginTransmission(devAddr);
                useWire->write(regAddr);