6 years ago.

You first need to set the register from which to read and then read a byte from that register. Normally, multiple sequential read operations would automatically increment the selected register address and thus read from the next sequential register. However, the specific register address for ''sequence 4'' is linked to an internal fifo and every subsequent read operation does not access the next register, but instead sends the next value in the fifo. The problem with your code is that you read only one byte from the fifo, the master does not send an acknowledge since it is the last byte, and it does not send a Stop because you set the 'repeated start' parameter to 'true'.

Try this:

//reg = address of fifo
//set the register address, select repeated start for the follow-on read
i2c.write((int)((KX224_DEVICE_ADDRESS_1E << 1) | I2C_WRITE),  &reg, 1,  true);


//now read multiple bytes from the fifo register (10 in this case), make sure there is enough room in the buffer ''out'' for all 10
//dont use repeated start
char out[16];
int c = i2c.read((int)((KX224_DEVICE_ADDRESS_1E << 1) | I2C_READ), &out, 10);

//buffer out[0..9] now holds the 10 bytes from the fifo register

BTW you dont need to set the read/write bit in the slaveaddress. That is handled by the i2C lib. Just use:

...
i2c.write ((KX224_DEVICE_ADDRESS_1E << 1),  &reg, 1,  true);

..
int c = i2c.read ((KX224_DEVICE_ADDRESS_1E << 1), &out, 10);

i2c.frequency(400000);

char reg = 0x08;   //  magic byte 00001xxx
char out[16]; //buffer

//send magic byte, and dummy byte, select repeated start for the follow-on read
//use repeated start
i2c.write (reg,  out,  0, true);
 
//set the new freq (note: might be too high or not work...)
i2c.frequency (3000000); 

//now prepare to read from the fifo register
//use repeated start
reg = fifo read address;   // set the fifo address
int c = i2c.write( (int)(KX224_DEVICE_ADDRESS_1E << 1), &reg, 1, true);

//now read multiple bytes from the fifo register (10 in this case), make sure there is enough room in the buffer ''out'' for all 10
//dont use repeated start
int c = i2c.read( (int)(KX224_DEVICE_ADDRESS_1E << 1),  out, 10);
 
//restore the freq 
i2c.frequency (100000);