"Occasionally a blocking open of dcm port 0 will hang in ttyopen()
waiting for carrier detect to be asserted when it's already
present.
The problem is that dcmmint() will return before updating the
value of sc->sc_mcndlast if the device is not open. If carrier
detect drops after the device is closed, sc->sc_mcndlast will
no longer correctly represent the "previous" state of the
signals when the next transition of carrier detect occurs.
A subsequent blocking open will wait forever for an event
which has in fact taken place."
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