[ntp:hackers] More on the looping problems with some FreeBSD systems
David L. Mills
mills at udel.edu
Wed Apr 27 19:11:19 PDT 2005
Guys,
I've had two incidents where a reference clock driver got in an I/O loop
and a report about an ACTS driver doint what might be the same thing.
The problem occurs at or shortly after the open and before or at the
first read. It looks like an I/O interrupt isn't being cleard and a
continuous stream of zero-length buffers is happening. I'm no expert on
Unix I/O code, but I did trace through the select() loop and don't see a
smoking gun. O do suspect, however, that the interrupt stream is coming
from the driver, perhaps due to modem control lines. Note I have some
machines that work fine the way things are and two that don't. Same
machine, same configuration, same radio.
On that assumption I pulled all the pins out of the interface cable
except the TXD and RXD data pins. That did in fact fix the problem.
However, it is not clear that something in the refclock setup procedure
might be twiddling a modem control line that sets off a bug in the port
driver. It would be wise if somebody with Knowledge checked the port
driver looking for little evils that might occur with various
manufacture of 16550 or 8250 UARTs or whatever else folks. use.
Dave
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