Operating instructions
M300USERSGUIDE SEA
GENERALINFORMATION
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• M300 interfaces directly with BC635PCI/BC637PCI (GPS Mode) interface (IRIG-A, IRIG-B, IEEE 1344
(Modulated or DCLS). There are no drivers to talk to the BC635PCI/BC637PCI interface in QNX 4.
• In general, time adjustments when M300 is running causes issues, mostly with data triggers. If the time
adjustment is forward, usually it's not too bad. But if we make a backwards adjustment in time, then this
causes problems with the triggers (specifically the time/frequency property).
• Different times used are M300 time (System/SBUS interface), QNX 4 time (PC internal clock),
BC635PCI/BC637PCI time, NTP (network based) and GPS (either via NMEA serial data or hookup to
BC637PCI).
Normal M300 operation.
• In acquisition initialization M300 reads either QNX 4 clock or BC635PCI/BC637PCI time. This depends
on the mode selected in the System board setup. This is used as the starting time for M300. If BC635PCI/
BC637PCI is in fly wheeling then QNX 4 clock is used.
• In the IRQ 3 handler we increment time and keep track of time. This time (M300 time) will be different
than QNX 4 time.
• In the IRQ 3 handler, we also read the QNX 4 time once per second.
• In the proxy, once per second, we check to see if there is a time drift between BC635PCI/BC637PCI time
or M300 time and QNX 4 time. If the difference is less than 100 ms, we do a small adjust to the QNX 4
clock over time. Otherwise we just set the QNX 4 clock to the BC635PCI/BC637PCI time or M300 time.
We use BC635PCI/BC637PCI time is not in fly wheeling mode or using external clock source. Otherwise
we use M300 time.
• If we are using BC635PCI/BC637PCI (not in fly wheeling mode or we are using external clock source). In
the proxy, once per second, we also check to see if the M300 time and BC635PCI/BC637PCI time differ. If
the difference is outside the time limit provided in the System Board Setup, then we reset the M300 time
with BC635PCI/BC637PCI time.
BC635PCI/BC637PCI card interface setup (M300 board initialization).
• Setup mode (user selects mode).
• Set year using value from QNX 4 system.
• Set local offset.
• Set year auto increment.
• Set local time observe flag.
• If the time is fly wheeling mode, then we set the time to the card with QNX 4 time.
• Set the heartbeat (this uses n1 and n2 values). We compute these from maximum system frequency.
Synchronize to other systems.