BlackZork
commented
4 months ago As for MQTT -> Modbus write commands are always executed. If you see other behavior, then it is a bug.
For Modbus -> MQTT I agree, it should be configurable on mqtt level and topic level. It may be also useful for debugging purposes.
JayHerpin
There are a few use cases when this is beneficial.
Modbus -> MQTT:
It is sometimes useful to have the timestamp of values updating those values are not changing. Consider the simple task so plotting the value of some value vs time. In the current implementation, doing this would require obersving changes in the "availability" of a particular value and assuming that the value had not changed because it still says it is available and no update had been received. While doable, it needlessly complicates the issue.
MQTT -> Modbus:
Consider the case where a register may have multiple writers or can otherwise value outside the view of mqmgateway. Given as mqmgateway will presumably always be used within the scope of some larger application or system, if that application or system wants to forcefully set some particular register to some value, a common way to do this might be to write that periodically. However, given that mqmgateway will discard operations that appear to have no effect, subsequent writes of the same value become ineffective. If the register in question where to change without that change being passed through mqmgateway then the larger application would effectively be unable to enforce its desired state.
Ideally there would be a setting that could enable/disable this behavior. While having the ability to control this per topic would be ideal, having it as a singular application wide setting would be better than nothing.