Dear all,
       I'm writing a very simple device driver starting from the nulldev.cxx 
example. 

I define an equipment as reported at the end of this message then, if all 
variables are Input variables, I define them with:

  mdevice device("myEquimpent", "Input", DF_INPUT | DF_MULTITHREAD, mydevice);
  device.define_var("Var1", 0.1);
  device.define_var("Var2", 0.1);
  ...

If all variables are output variables, I define them with:

  mdevice device("myEquipment", "Output", DF_OUTPUT | DF_MULTITHREAD, mydevice);
  device.define_var("Var1", 0.1);
  device.define_var("Var2", 0.1);

But I don't know what to do if I have mixed input and output variables in the same 
device. I think I can do:

  mdevice device_in("myEquipment", "Input", DF_INPUT | DF_MULTITHREAD, mydevice);
  device.define_var("Var1", 0.1);

  mdevice device_out("myEquipment", "Output", DF_OUTPUT | DF_MULTITHREAD, 
mydevice);
  device.define_var("Var2", 0.1);

but in this case, inside mydevice.cxx, I don't know how to distinguish Var1 and 
Var2, because they are both identified as channel 0.

Do you have any suggestion?

Thank you,
      Francesco




-------------------------------------------------------------------



   {"SourceMotor",                       /* equipment name */
    {7, 0,                       /* event ID, trigger mask */
     "SYSTEM",                  /* event buffer */
     EQ_SLOW,                   /* equipment type */
     0,                         /* event source */
     "MIDAS",                   /* format */
     TRUE,                      /* enabled */
     RO_ALWAYS,        /* read when running and on transitions */
     60000,                     /* read every 60 sec */
     0,                         /* stop run after this event limit */
     0,                         /* number of sub events */
     1,                         /* log history every event */
     "", "", ""} ,
    cd_multi_read,                 /* readout routine */
    cd_multi,                      /* class driver main routine */
   },

The "multi" class driver takes care of that. It properly calls the SET and GET functions 
with the correct index. The code for that is in multi.cxx:105:

 device_driver(m_info->driver_input[i], CMD_GET,
               i - m_info->channel_offset_input[i],
               &m_info->var_input[i]);

The "channel_offset_input" and "channel_offset_output" store the first index of the 
channel in the overall ODB array (where inputs and outputs are staggered together), so 
the device_driver is always called with an index 0...n each for input and output, but 
with different commands CMD_GET and CMD_SET. You can take the mscbdev.cxx device driver 
as a working example.

Stefan

Dear all, does anyone have an example of for a device driver using modbus or modbus tcp to communicate with a device and willing to share it? Thanks.

> Dear all, does anyone have an example of for a device driver using modbus or modbus tcp to communicate with a device and willing to share it? Thanks.

I have not seen any modbus devices recently, so all my code and examples are quite old.

Basic modbus/tcp communication driver is in the midas repo:

daq00:midas$ find . | grep -i modbus
./drivers/divers/ModbusTcp.cxx
./drivers/divers/ModbusTcp.h
daq00:midas$ 

This driver worked for communication to a modbus PLC (T2K/ND280/TPC experiment in Japan).

An example program to use this driver and test modbus communication is here:
https://bitbucket.org/expalpha/agdaq/src/master/src/modbus.cxx

Because at the end, we do not have any modbus devices in any recent experiment,
I do not have any example of using this driver in the midas frontend. Sorry.

K.O.

let notification = new Notification('MIDAS Message', {
    body: text,
});

<button class="mbutton" onclick="Notification.requestPermission()">Request notification permission</button>

Asume you have a variable foo and a link bar -> foo. When you go to the ODB in
mhttpd, click "Delete" and select bar, it actually deletes foo. bar stays,
stating "<cannot resolve link>". Trying the same in odbedit with rm gives the
expected result (bar is gone, foo is still there).

I'm on the develop branch.

> Asume you have a variable foo and a link bar -> foo. When you go to the ODB in
> mhttpd, click "Delete" and select bar, it actually deletes foo. bar stays,
> stating "<cannot resolve link>". Trying the same in odbedit with rm gives the
> expected result (bar is gone, foo is still there).
> 
> I'm on the develop branch.

I think I can confirm this. Created a bug report on bitbucket:

https://bitbucket.org/tmidas/midas/issues/148/mhttpd-odb-editor-deletes-wrong-symlink

K.O.

> > Asume you have a variable foo and a link bar -> foo. When you go to the ODB in
> > mhttpd, click "Delete" and select bar, it actually deletes foo. bar stays,
> > stating "<cannot resolve link>". Trying the same in odbedit with rm gives the
> > expected result (bar is gone, foo is still there).
> > 
> > I'm on the develop branch.
> 
> I think I can confirm this. Created a bug report on bitbucket:
> 
> https://bitbucket.org/tmidas/midas/issues/148/mhttpd-odb-editor-deletes-wrong-symlink
> 
> K.O.

I fixed this and committed the change. Took me a while since it was in KO's code.

Stefan

Another problem while using odbedit.
I tried the batch mode of "odbedit". I created a key as "/A_Str" by mistake and 
wanted to delete it. Then "odbedit" failed to accept the "Return" key. Please see 
the screen-shot attached. :-(

> Another problem while using odbedit.
> I tried the batch mode of "odbedit". I created a key as "/A_Str" by mistake and 
> wanted to delete it. Then "odbedit" failed to accept the "Return" key. Please see 
> the screen-shot attached. :-(

This bug has been fixed in the latest repository.
I encountered it in svn-r4488.

12:51:20.154 2025/02/19 [SC Frontend,ERROR] [mfe.cxx:620:register_equipment,ERROR] Write cache size mismatch for buffer "SYSTEM": equipment "Environment" asked for 0, while eqiupment "LED" asked for 10000000
12:51:20.154 2025/02/19 [SC Frontend,ERROR] [mfe.cxx:620:register_equipment,ERROR] Write cache size mismatch for buffer "SYSTEM": equipment "LED" asked for 10000000, while eqiupment "Xenon" asked for 0

   {"Trigger",               /* equipment name */
      {1, 0,                 /* event ID, trigger mask */
         "SYSTEM",           /* event buffer */
         EQ_POLLED,          /* equipment type */
         0,                  /* event source */
         "MIDAS",            /* format */
         TRUE,               /* enabled */
         RO_RUNNING |        /* read only when running */
         RO_ODB,             /* and update ODB */
         100,                /* poll for 100ms */
         0,                  /* stop run after this event limit */
         0,                  /* number of sub events */
         0,                  /* don't log history */
         "", "", "", "", "", 0, 0},
      read_trigger_event,    /* readout routine */
      10000000,              /* write cache size */
   },

fe_set_write_case(int size);

I think I added the cache size correctly:

  {"Trigger",               /* equipment name */
      {1, 0,                 /* event ID, trigger mask */
         "SYSTEM",           /* event buffer */
         EQ_POLLED,          /* equipment type */
         0,                  /* event source */
         "MIDAS",            /* format */
         TRUE,               /* enabled */
         RO_RUNNING |        /* read only when running */
         RO_ODB,             /* and update ODB */
         100,                /* poll for 100ms */
         0,                  /* stop run after this event limit */
         0,                  /* number of sub events */
         0,                  /* don't log history */
         "", "", "", "", "", // frontend_host, name, file_name, status, status_color
         0, // hidden
         0  // write_cache_size <<--------------------- set this to zero -----------
      },
   }

K.O.

the main purpose of the event buffer write cache is to prevent high contention for the 
event buffer shared memory semaphore in the pathological case of very high rate of very 
small events.

there is a computation for this, I have posted it here several times, please search for 
it.

in the nutshell, you want the semaphore locking rate to be around 10/sec, 100/sec 
maximum. coupled with smallest event size and maximum practical rate (1 MHz), this 
yields the cache size.

for slow control events generated at 1 Hz, the write cache is not needed, 
write_cache_size value 0 is the correct setting.

for "typical" physics events generated at 1 kHz, write cache size should be set to fit 
10 events (100 Hz semaphore locking rate) to 100 events (10 Hz semaphore locking rate).

unfortunately, one cannot have two cache sizes for an event buffer, so typical frontends 
that generate physics data at 1 kHz and scalers and counters at 1 Hz must have a non-
zero write cache size (or semaphore locking rate will be too high).

the other consideration, we do not want data to sit in the cache "too long", so the 
cache is flushed every 1 second or so.

all this cache stuff could be completely removed, deleted. result would be MIDAS that 
works ok for small data sizes and rates, but completely falls down at 10 Gige speeds and 
rates.

P.S. why is high semaphore locking rate bad? it turns out that UNIX and Linux semaphores 
are not "fair", they do not give equal share to all users, and (for example) an event 
buffer writer can "capture" the semaphore so the buffer reader (mlogger) will never get 
it, a pathologic situation (to help with this, there is also a "read cache"). Read this 
discussion: https://stackoverflow.com/questions/17825508/fairness-setting-in-semaphore-
class

K.O.

> the main purpose of the event buffer write cache

how to control the write cache size:

1) in a frontend, all equipments should ask for the same write cache size, both mfe.c and 
tmfe frontends will complain about mismatch

2) tmfe c++ frontend, per tmfe.md, set fEqConfWriteCacheSize in the equipment constructor, in 
EqPreInitHandler() or EqInitHandler(), or set it in ODB. default value is 10 Mbytes or value 
of MIN_WRITE_CACHE_SIZE define. periodic cache flush period is 0.5 sec in 
fFeFlushWriteCachePeriodSec.

3) mfe.cxx frontend, set it in the equipment definition (number after "hidden"), set it in 
ODB, or change equipment[i].write_cache_size. Value 0 sets the cache size to 
MIN_WRITE_CACHE_SIZE, 10 Mbytes.

4) in bm_set_cache_size(), acceptable values are 0 (disable the cache), MIN_WRITE_CACHE_SIZE 
(10 Mbytes) or anything bigger. Attempt to set the cache smaller than 10 Mbytes will set it 
to 10 Mbytes and print an error message.

All this is kind of reasonable, as only two settings of write cache size are useful: 0 to 
disable it, and 10 Mbytes to limit semaphore locking rate to reasonable value for all event 
rate and size values practical on current computers.

In mfe.cxx it looks to be impossible to set the write cache size to 0 (disable it), but 
actually all you need is call "bm_set_cache_size(equipment[0].buffer_handle, 0, 0);" in 
frontend_init() (or is it in begin_of_run()?).

K.O.

> > the main purpose of the event buffer write cache
> how to control the write cache size:

OP provided insufficient information to say what went wrong for them, but do try this:

1) in ODB, for all equipments, set write_cache_size to 0
2) in the frontend equipment table, set write_cache_size to 0

That is how it is done in the example frontend: examples/experiment/frontend.cxx

If this configuration still produces an error, we may have a bug somewhere, so please let us know how it shakes out.

K.O.

 > All this is kind of reasonable, as only two settings of write cache size are useful: 0 to 
> disable it, and 10 Mbytes to limit semaphore locking rate to reasonable value for all event 
> rate and size values practical on current computers.

Indeed KO is correct that only 0 and 10MB make sense, and we cannot mix it. Having the cache setting in the equipment table is 
cumbersome. If you have 10 slow control equipment (cache size zero), you need to add many zeros at the end of 10 equipment 
definitions in the frontend. 

I would rather implement a function or variable similar to fEqConfWriteCacheSize in the tmfe framework also in the mfe.cxx 
framework, then we need only to add one line llike

gEqConfWriteCacheSize = 0;

in the frontend.cxx file and this will be used for all equipments of that frontend. If nobody complains, I will do that in April when I'm 
back from Japan.

Stefan