CSR_TCFG_VAL
delta &= CSR_TCFG_VAL;
timer_config = period & CSR_TCFG_VAL;
write_gcsr_timertick(CSR_TCFG_VAL);
period = cfg & CSR_TCFG_VAL;
val = msec_to_cycles(msec) & CSR_TCFG_VAL;