SR_BRK
sr &= SR_PE | SR_FE | SR_OVR | SR_BRK;
if (sr & SR_BRK) {
if (sr & SR_BRK)
port->read_status_mask |= SR_BRK;
port->ignore_status_mask |= SR_BRK;
port->ignore_status_mask |= SR_PE | SR_OVR | SR_FE | SR_BRK;