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];
------------------------------------------------------------------------------