Method readBytes

lib/i2cdev/I2Cdev.cpp:209–316

Read multiple bytes from an 8-bit device register. * @param devAddr I2C slave device address * @param regAddr First register regAddr to read from * @param length Number of bytes 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 bytes read (-1

 * @return Number of bytes read (-1 indicates failure)
 */
int8_t I2Cdev::readBytes(uint8_t devAddr, uint8_t regAddr, uint8_t length, uint8_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(" bytes 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 (int k = 0; k < length; k += min((int)length, I2CDEVLIB_WIRE_BUFFER_LENGTH)) {
                useWire->beginTransmission(devAddr);
                useWire->send(regAddr);
                useWire->endTransmission();
                useWire->beginTransmission(devAddr);
                useWire->requestFrom((uint8_t)devAddr, (uint8_t)min((int)length - k, I2CDEVLIB_WIRE_BUFFER_LENGTH));

                for (; useWire->available() && (timeout == 0 || millis() - t1 < timeout); count++) {
                    data[count] = useWire->receive();
                    #ifdef I2CDEV_SERIAL_DEBUG
                        Serial.print(data[count], HEX);
                        if (count + 1 < length) Serial.print(" ");
                    #endif
                }
            }
        #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 (int k = 0; k < length; k += min((int)length, I2CDEVLIB_WIRE_BUFFER_LENGTH)) {
                useWire->beginTransmission(devAddr);
                useWire->write(regAddr);
                useWire->endTransmission();
                useWire->beginTransmission(devAddr);
                useWire->requestFrom((uint8_t)devAddr, (uint8_t)min((int)length - k, I2CDEVLIB_WIRE_BUFFER_LENGTH));
        
                for (; useWire->available() && (timeout == 0 || millis() - t1 < timeout); count++) {
                    data[count] = useWire->read();
                    #ifdef I2CDEV_SERIAL_DEBUG
                        Serial.print(data[count], HEX);
                        if (count + 1 < length) Serial.print(" ");