I8254_CTRL_SEL_CTR
__i8254_write(i8254, I8254_CTRL_SEL_CTR(counter) | I8254_CTRL_LATCH,
byte = I8254_CTRL_SEL_CTR(counter) | /* select counter */
#define I8254_CTRL_READBACK(x) (I8254_CTRL_SEL_CTR(3) | BIT(x))