Experimental Physics and
Industrial Control System

Michael Davidsaver via Tech-talk <tech-talk at aps.anl.gov> · Tue, 17 Mar 2020 14:07:07 -0700

On 3/17/20 9:13 AM, Di Wang wrote:
> Hi Michael,
> 
>   I found an event lost situation in my MRF VME-EVR-230RF,

Can you clarify "lost"?  Do you seen any messages being logged?
Are either the hardware or software FIFO overflow counters incrementing
when this happens?

Also, have you verified, by configuring an LED or output, that
event 125 is actually being received?

> so I am wondering how will mrfioc2 handle the event received right after the timestamp reset event (i.e. 125) ?

This should not make a difference as far as software is concerned.
The EVRMRM::seconds_tick method you link below is executed here:

https://github.com/epics-modules/mrfioc2/blob/7bee26590cb5fea8117d0a12920bc281ab1c7cd8/evrMrmApp/src/drvem.cpp#L1317

So it is executed by the thread servicing the hardware event FIFO.
However, it doesn't alter the entries being read.  It only acts to
cross-check the new seconds value to make sure that is has incremented
by one from the previous value.  Allowing corrupt timestamps into
generalTime has been known to cause strange issues.

> We might send event code only 1 tick (i.e. 9 nanosecond) later than before one, so the 'right after' could be very fast. Here is a brief example.
> 
> Event       Timestamp
> 1           953053925.999,917,620
> 125       953053925.999,977,626  <-----TS reset event
> 2 <-----lost, and the timestamp should be 953053926.999,977,650
> 3            953053926.000,100,043
> 4            953053926.000,450,210
> 
> 
>   I understand that when TS reset event is received the 32-bit seconds register will be reset, and below callback function would be called, but I still do not understand the process logic and the reason of event lost.

Can I assume that the source of event 125 is asynchronous to the others?
That is, a real GPS receiver, as opposed to some kind of loopback for testing?

Are there any other event codes which are going over the link?
"120 events" is mentioned below, though the more important question
is how frequently these are sent, and how many asynchronous sources
are involved.

One explanation would be if the event link was too busy, and events
were being lost at the EVG due to the limited buffering at the
priority encoder.  Unfortunately, I don't believe there will be any
indication if this is happening other than missing events.

> https://github.com/epics-modules/mrfioc2/blob/7bee26590cb5fea8117d0a12920bc281ab1c7cd8/evrMrmApp/src/drvem.cpp#L1430
> 
>   For you convenience, some information might help:
> epics 3.15.5, devlib 2-2.10, mrfioc 2-2.2.0 (I added several functions to buffer the events in drvem.cpp)
> event clock: 114 MHz, repetition rate: 50 Hz, more than 120 events are monitored
> 
> Regards,
> Di WANG
> Linac Control Group, KEK
> 

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System