Science event telemetry begins before bias map has been telemetered, overloading direct memory transfers from one or more FEPs, resulting in locked values for the FEP Threshold Plane.
Three times:
Most likely not. The untricklebias patch, installed in Flight Software
Version B-opt-C in 2003, calls all biasThief methods from within the
science thread, preventing simultaneous telemetry of bias and event
packets.
We are speaking of two symptoms, interleaved bias and event packets, and frozen threshold crossing values. The most immediately obvious symptom is saturated telemetry, with far too many events from the affected FEP or FEPs. On an affected FEP, the threshold crossing counts will not change from one frame to the next. The symptoms disappear with the next science run, and may become apparent only when SSR data are examined.
In 2001, the response was to recycle FEP power. This is now automatically built into the start of each SI mode command sequence, and is unnecessary. The subsequent science run in the load will execute normally, so no corrective action is necessary.
If we see T-Plane latchup on coming into comm, it may be worth trying
to salvage the remainder of the science run. Check whether a CLD
exists for a WSPOWXXXXX packet to command the required set of DEA boards
and FEPs. If so, and significant time remains for the obsid, execute
stop science, WSFEPALLDN, the WSPOWXXXXX command, and start science.
A special case: if the following science run is a no-bias version of
the same SI mode, it will not recycle the FEP power. Send a stop
science and a WSFEPALLDN command to ACIS.
Afterward, the team may examine the telemetry stream at leisure to see what may have triggered the latchup. If there was no interleaving of bias and events, look for any other simultaneous high demand on DMA transfers out of the affected FEPs.
Once the T-Plane latches, science will be lost from the latched FEPs for the rest of the science run, and some science is likely to be lost from remaining FEPs due to telemetry saturation.
1A_AA000_191.CLD, AA00000000 (stop science command)1A_WS003_165.CLD, WSFEPALLDN (command to power down all FEPs)Currently there are 2 6-chip and 3 5-chip power commands in CLDs. The 5-chip commands all power an additional, unneeded FEP.