MIDAS history is very simple:
from your frontend, your write your history data to ODB /eq/xxx/variables (see below)
mlogger has a hotlink to all /eq/*/variables and it will "see" the new data, write it to history file (see below)
you should see the history file grow using "ls"
history web page in your browser sends a "give me more data" JSON-RPC request to mhttpd
mhttpd looks at the history file, if there is new data (file got bigger) it send it to the web page
web page shows the new data.
where things usually go wrong:
- mlogger only looks for new history variables on startup and on begin-of-run. if you add new stuff in your frontend, you
will not see it until you restart mlogger or start a new run.
- mlogger only looks at history data if corresponding "/eq/xxx/common/log history" is non-zero. for best effect, set it to
"1". (or "0" to turn history off).
- history file is not growing, likely mlogger does not "see" your new data
- timestamps of stuff in /eq/xxx/variables are not getting updated, likely frontend is not writing them, and there is no
new data for mlogger to "see" and write to file.
Frontend has several ways of writing to /eq/xxx/variables:
- write to ODB directly using ODB API db_set_data(), mvodb->Wx(), etc. this is the most foolproof method. use in
conjunction with a printf() statement to make sure you actually do write to ODB. Sometimes your frontend event loop fails
to run, a bug/failure that has nothing to do with midas history.
- generate a midas event and set the per-equipment "write event to ODB" flag (RO_ODB for mfe.c frontends), the mfe/tmfe
framework will write event data to ODB, each data bank will be written to /eq/xxx/variables/BANKNAME, data type is taken
from the event data bank definition.
This second method sometimes malfunctions, typical problems are missing RO_ODB in the equipment table, equipment table in
ODB overwriting the value in source code (this is confusing in mfe.c frontends).
Least likely failure is "/eq/xxx/common/log history" set to bogus value. Normal values are 0=history disabled, 1=history
enabled, other values are only needed if you do not want mlogger to record history as often as you generate it, i.e. you
update /eq/xxx/variables every 1/sec, but you want mlogger to only record it 1/minute.
I hope this helps.
P.S. I notice your equipment tables do not have RO_ODB, so if you use the 2nd method, write history via event data banks,
it will not work.
K.O.
> Dear MIDAS developers,
>
> I'm trying to understand handling of the history (slow control) variables in MIDAS,
> and it seems that the behavior I'm observing is somewhat counterintuitive.
> Most likely, I just do not understand the implemented logic.
>
> As it it rather difficult to report on the behavior of the interactive program,
> I'll describe what I'm doing and illustrate the report with the series of attached
> screenshots showing the history plots and the status of the run control at different
> consecutive points in time.
>
> Starting with the landscape:
>
> - I'm running MIDAS, git commit=30a03c4c (the latest, as of today).
>
> - I have built the midas/examples/slowcont frontend with the following modifications.
> (the diffs are enclosed below):
>
> 1) the frequency of the history updates is increased from 60sec/10sec to 6sec/1sec
> and, in hope to have updates continuos, I replaced (RO_RUNNING | RO_TRANSITIONS)
> with RO_ALWAYS.
>
> 2) for convenience of debugging, midas/drivers/nulldrv.cxx is replaced with its clone,
> which instead of returning zeroes in each channel, generates a sine curve:
>
> V(t) = 100*sin(t/60)+10*channel
>
> - an active channel in /Logger/History is chosen to be FILE
>
> - /History/LoggerHistoryChannel is also set to FILE
>
> - I'm running mlogger and modified, as described, 'scfe' frontend from midas/examples/slowcont
>
> - the attached history plots include three (0,4 and 7) HV:MEASURED channels
>
>
> Now, the observations:
>
> 1) the history plots are updated only when a new run starts, no matter how hard
> I'm trying to update them by clicking on various buttons.
>
> The attached screenshots show the timing sequence of the run control states
> (with the times printed) and the corresponding history plots.
>
> The "measured voltages" change only when the next run starts - the voltage graphs
> break only at the times corresponding to the vertical green lines.
>
> 2) No matter for how long I wait within the run, the history updates are not happening.
>
> 3) if the time difference between the two run starts gets too large,
> the plotted time dependence starts getting discontinuities
>
> 4) finally, if I switch the logging channel from FILE to MIDAS (activate the MIDAS
> channel in /Logger/History and set /History/LoggerHistoryChannel to MIDAS),
> the updates of the history plots simply stop.
>
> MIDAS feels as a great DAQ framework, so I would appreciate any suggestion on
> what I could be doing wrong. I'd also be happy to give a demo in real time
> (via ZOOM/SKYPE etc).
>
> -- much appreciate your time, thanks, regards, Pasha
>
> ------------------------------------------------------------------------------
> diff --git a/examples/slowcont/scfe.cxx b/examples/slowcont/scfe.cxx
> index 11f09042..c98d37e8 100644
> --- a/examples/slowcont/scfe.cxx
> +++ b/examples/slowcont/scfe.cxx
> @@ -24,9 +24,10 @@
> #include "mfe.h"
> #include "class/hv.h"
> #include "class/multi.h"
> -#include "device/nulldev.h"
> #include "bus/null.h"
>
> +#include "nulldev.h"
> +
> /*-- Globals -------------------------------------------------------*/
>
> /* The frontend name (client name) as seen by other MIDAS clients */
> @@ -74,11 +75,11 @@ EQUIPMENT equipment[] = {
> 0, /* event source */
> "FIXED", /* format */
> TRUE, /* enabled */
> - RO_RUNNING | RO_TRANSITIONS, /* read when running and on transitions */
> - 60000, /* read every 60 sec */
> + RO_ALWAYS, /* read when running and on transitions */
> + 6000, /* read every 6 sec */
> 0, /* stop run after this event limit */
> 0, /* number of sub events */
> - 10000, /* log history at most every ten seconds */
> + 1000, /* log history at most every one second */
> "", "", ""} ,
> cd_hv_read, /* readout routine */
> cd_hv, /* class driver main routine */
> @@ -93,8 +94,8 @@ EQUIPMENT equipment[] = {
> 0, /* event source */
> "FIXED", /* format */
> TRUE, /* enabled */
> - RO_RUNNING | RO_TRANSITIONS, /* read when running and on transitions */
> - 60000, /* read every 60 sec */
> + RO_ALWAYS, /* read when running and on transitions */
> + 6000, /* read every 6 sec */
> 0, /* stop run after this event limit */
> 0, /* number of sub events */
> 1, /* log history every event as often as it changes (max 1 Hz) */
> ------------------------------------------------------------------------------
> [test_001]$ diff ../midas/examples/slowcont/nulldev.cxx ../midas/drivers/device/nulldev.cxx
> 13d12
> < #include <math.h>
> 150,154c149,150
> < if (channel < info->num_channels) {
> < // *pvalue = info->array[channel];
> < time_t t = time(NULL);;
> < *pvalue = 100*sin(M_PI*t/60)+10*channel;
> < }
> ---
> > if (channel < info->num_channels)
> > *pvalue = info->array[channel];
> ------------------------------------------------------------------------------ |