Changes of integer input of FMU are ignored

[anatoly.trosinenko@…]

When simulating an FMU with an integer input that should trigger when condition in algorithm block, changes are ignored but the input is passed through correctly.

How to reproduce

TestInt.mo:

model TestInt
  input Integer inInt;
  output Integer outInt;
  output Integer passthrough;
initial equation
  outInt = 0;
algorithm
  when inInt > pre(inInt) then
    outInt := outInt + 1;
  end when;
equation
  passthrough = inInt;
end TestInt;

TestInt.mos:

print(buildModelFMU(TestInt, "1.0", "me"));
print(getErrorString());

input.csv:

time;inInt
0.0;0
0.7;1
0.8;2

Compile it with

$ omc TestInt.mos TestInt.mo
/home/trosinenko/TestInt.fmu

$ ...

Simulate with FMUChecker (tested with 2.0.3):

$ path/to/fmuCheck.linux64 -i input.csv TestInt.fmu           
[INFO][FMUCHK] FMI compliance checker Test [FMILibrary: Test] build date: Dec 19 2016
[INFO][FMUCHK] Called with following options:
[INFO][FMUCHK] /path/to/fmuCheck.linux64 -i input.csv TestInt.fmu
[INFO][FMUCHK] Will process FMU TestInt.fmu
[INFO][FMILIB] XML specifies FMI standard version 1.0
[INFO][FMUCHK] Model name: TestInt
[INFO][FMUCHK] Model identifier: TestInt
[INFO][FMUCHK] Model GUID: {344d6ea1-babe-4fab-a4f1-a7a6ef710740}
[INFO][FMUCHK] Model version: 
[INFO][FMUCHK] FMU kind: ModelExchange
[INFO][FMUCHK] The FMU contains:
0 constants
0 parameters
3 discrete variables
1 continuous variables
1 inputs
2 outputs
1 internal variables
0 variables with causality 'none'
0 real variables
3 integer variables
0 enumeration variables
1 boolean variables
0 string variables

[INFO][FMUCHK] Printing output file header
"time","outInt","passthrough"
[INFO][FMUCHK] Opening input file input.csv
[INFO][FMUCHK] Detected separator character in input file: ;
[INFO][FMILIB] Loading 'linux64' binary with 'standard32' platform types
[INFO][FMUCHK] Version returned from FMU:   1.0
[INFO][FMUCHK] Initialized FMU for simulation starting at time 0
0.0000000000000000E+00,0,0
2.0000000000000000E-03,0,0
4.0000000000000001E-03,0,0
...
7.9600000000000004E-01,0,1
7.9800000000000004E-01,0,1
8.0000000000000004E-01,0,2
8.0200000000000005E-01,0,2
...
9.9600000000000022E-01,0,2
9.9800000000000022E-01,0,2
1.0000000000000000E+00,0,2
[INFO][FMUCHK] Simulation finished successfully at time 1
FMU check summary:
FMU reported:
        0 warning(s) and error(s)
Checker reported:
        0 Warning(s)
        0 Error(s)

Changing line

  when inInt > pre(inInt) then

to

  when change(inInt) then

does not change behavior.

[anatoly.trosinenko@…]

Possibly related: #5149

Workaround for this bug: replace

  when inInt > pre(inInt) then

with

  when passthrough > pre(passthrough) then

Then it works (except for that one need to add something like output Real x and der(x) = x equation, so it is validated in FMUChecker 2.0.4).

[anatoly.trosinenko@…]

Some random observations:

• when I change types of inInt and passthrough to Real, both expressions from the above mentioned workaround give the same stay-at-zero counter (which is not surprising because x > pre(x) for continuous Real variables is quite strange)
• adding +d=newInst to the command line does not change anything

For slightly modified Test.mo:

model Test
  input Integer inInt;
  output Integer outInt, o;
  output Integer passthrough;
initial equation
  outInt = 0;
  o = 0;
algorithm
  when inInt > pre(inInt) then
    outInt := outInt + 1;
  end when;
  when passthrough > pre(passthrough) then
    o := o + 1;
  end when;
equation
  passthrough = inInt;
end Test;

... looking at the generated Test.c after executing omc -s ../Test.mo, I see the following

/*
 equation index: 9
 type: SIMPLE_ASSIGN
 passthrough = inInt
 */
void Test_eqFunction_9(DATA *data, threadData_t *threadData)
{
  TRACE_PUSH
  const int equationIndexes[2] = {1,9};
  data->localData[0]->integerVars[3] /* passthrough DISCRETE */ = (modelica_integer)data->localData[0]->integerVars[0] /* inInt variable */;
  TRACE_POP
}
/*
 equation index: 10
 type: ALGORITHM
 
   o := pre(o);
   $whenCondition2 := pre($whenCondition2);
   outInt := pre(outInt);
   $whenCondition1 := pre($whenCondition1);
   $whenCondition1 := false;
   when $whenCondition1 then
     outInt := outInt + 1;
   end when;
   $whenCondition2 := passthrough > pre(passthrough);
   when $whenCondition2 then
     o := o + 1;
   end when;
 */
void Test_eqFunction_10(DATA *data, threadData_t *threadData)
{
    ...
}

I see two interesting points here:

• $whenCondition1 is explicitly assigned false just before usage in Modelica pseudocode (so it looks not like just a bug in the fmi runtime)
• the passthrough variable is shown as DISCRETE, while inInt is just a variable, just like non-discrete Reals from the example above. On the other hand, passthrough is annotated as discrete by default (this is, again, logical, since it is integral type)

[anatoly.trosinenko@…]

Seems like the issue #5149 about not being able to specify discrete input Integer inInt; is really connected to this one not by mere coincidence, since the lowerKnownVarkind function seems to be intentionally returning BackendDAE.VARIABLE() even for inherently-discrete types, and copy-pasting type-aware code from the lowerVarkind function leads to an error about mixed-determined system.

This issue looks quite insidious since it does not lead to compile-time or even run-time error -- just to (probably hard-to-debug) unexpected behaviors, so I humbly set the importance to critical :)

[Adrian Pop]

I made PR: ​https://github.com/OpenModelica/OMCompiler/pull/2742
with your suggested changes (also set String variables to discrete).
I will run the testsuite on it to see how many models this change breaks.