[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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