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1991-02-05
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16-SEPT-1988 Richard B. Johnson V1.06
Found bug in interrupt service routine where if both the line status
and modem status interrupts happened at the same time the UART would
ignore the lowest-priority interrupt (the modem status) forever. This
could occur when large files were being transferred and flow-control
was active. The program would hang forever waiting for the modem
status to change when, in fact, it had many hours ago. The work-
around was to read the modem status every time anything caused a
UART interrupt. This is one of the known "bugs" of the 8250 UART.
The bug is in the documentation. The UART is doing just what it was
told to do (which isn't what I wanted).