TX39_INTRENABLE3_REG
tx_conf_write(tc, TX39_INTRENABLE3_REG, 0);
iregs[3] = tx_conf_read(tc, TX39_INTRENABLE3_REG);
tx_conf_write(tc, TX39_INTRENABLE3_REG, 0);
tx_conf_write(tc, TX39_INTRENABLE3_REG, iregs[3]);