Why do I receive the error "Invalid Signal" when using "getsignal" from Simulink Real-Time in R2020a and earlier?

I'm trying to retrieve the value of a signal from my Simulink Real-Time (SLRT) model running on the target machine. However, "getsignal" claims that the signal does not exist - despite it being listed:

>> tg.load('rtapp');
>> tg.ShowSignals = 'on'

Target: TargetPC1
   Connected       = Yes
   Application     = rtapp
   Mode            = Real-Time Single-Tasking
   Status          = running
   CPUOverload     = none

   <...>

   Scopes          = 1
   NumSignals      = 2
   ShowSignals     = on
   Signals         = INDEX  VALUE       Type      BLOCK NAME      LABEL
                     0      1.000000    DOUBLE    Gain            myGain
                     1      0.737111    DOUBLE    Source block    mySource

   NumParameters   = 2
   ShowParameters  = off

>> tg.getsignal('myGain')
Error using xpctarget.xpc/getsignal
Invalid Signal

What am I doing wrong?

Answer 1

[MathWorks Support Team]

The SimulinkRealTime.target.getsignal function accepts either a signal ID or a SLRT signal name (block path) as the input. In this case, although "myGain" is the name of the Simulink signal, it is considered the label of the SLRT signal.

To access the signal by label, we must first access its signal ID, as follows:

>> sigID = tg.getsignalidsfromlabel('myGain');
>> tg.getsignal(sigID)

However, we recommend using "getsignal" with the block path instead of the signal label. For instance:

>> tg.getsignal('Gain')

This is a neater solution to access the signal compared to using the signal ID.

More information regarding accessing SLRT signals by name can be found in the documentation: https://www.mathworks.com/help/releases/R2020a/xpc/api/getsignal.html#d120e44386