GP_TCRR
bus_space_write_4(gptimer_iot, gptimer_ioh1, GP_TCRR, 0);
bus_space_write_4(gptimer_iot, gptimer_ioh0, GP_TCRR,
bus_space_write_4(gptimer_iot, gptimer_ioh0, GP_TCRR, UINT32_MAX);
oclock = bus_space_read_4(gptimer_iot, gptimer_ioh1, GP_TCRR);
clock = bus_space_read_4(gptimer_iot, gptimer_ioh1, GP_TCRR);
return bus_space_read_4(gptimer_iot, gptimer_ioh1, GP_TCRR);