TX39_INTRENABLE4_REG
tx_conf_write(tc, TX39_INTRENABLE4_REG, 0);
iregs[4] = tx_conf_read(tc, TX39_INTRENABLE4_REG);
tx_conf_write(tc, TX39_INTRENABLE4_REG, 0);
tx_conf_write(tc, TX39_INTRENABLE4_REG, iregs[4]);