FB_DALIVirtualCommunication

The individual DALI commands are temporarily stored in a command buffer within the Tc3_DALI library before further processing. The FB_DALIVirtualCommunication function block sequentially reads the DALI commands from this command buffer and forwards the DALI commands to the associated instances of FB_DALIVirtualControlGear.

One instance of the FB_DALIVirtualCommunication function block must be created for each DALI line that is to be simulated. This instance must be called in a separate, faster task. This faster communication task must have a higher priority than the task in which the function blocks for the individual DALI commands are called.

The utilization rate of the command buffer can be determined using the outputs of the function block. If you find that the command buffer is overflowing regularly, you should take the following steps:

How heavily are the individual PLC tasks utilized? TwinCAT provides suitable analysis tools.
Try reducing the cycle time of the task in which the FB_DALIVirtualCommunication function block is called. The value should not be greater than 6 ms. The optimum value is 2 ms or less.
Check the cycle time of the PLC task in which the function blocks for the individual DALI commands are called. This value should not be greater than 10 ms. The optimum value is 8 ms or less.
If possible avoid polling (regular reading) of values. Only read values when they are actually required.
Distribute the individual simulated DALI devices evenly over several DALI lines. Since several DALI lines are processed simultaneously in each PLC cycle, this increases the data throughput.

Inputs

VAR_INPUT
  bResetMaximumDemandCounter     : BOOL;
  bResetOverflowCounter          : BOOL;
  nOptions                       : DWORD := 0;
END_VAR

Name	Type	Description
bResetMaximumDemandCounter	BOOL	A positive edge resets the stored value for the maximum utilization of the command buffer, nBufferMaximumDemandMeter (0…100%).
ResetOverflowCounter	BOOL	A positive edge resets the stored value for the number of overflows of the command buffer, nBufferOverflowCounter.
nOptions	DWORD	Reserved for future extensions.

Outputs

VAR_OUTPUT
  bError                       : BOOL;
  ipResultMessage              : I_TcMessage;
  bBusy                        : BOOL;
  nBufferDemandMeter           : BYTE;
  nBufferMaximumDemandMeter    : BYTE;
  nBufferOverflowCounter       : UINT;
END_VAR

Name	Type	Description
bError	BOOL	This output is switched to TRUE if an error occurs during the execution. Further information about the error can be queried via the variable ipResultMessage. The output is set to FALSE again as soon as bBusy switches to TRUE.
ipResultMessage	I_TcMessage	Interface pointer (see error evaluation) that can be used to obtain detailed information about the processing of the function block (see runtime messages). The interface pointer is valid after bBusy has changed from TRUE to FALSE.
bBusy	BOOL	The output is set as soon as execution of the DALI commands has commenced. It remains active until all DALI commands have been processed.
nBufferDemandMeter	BYTE	Utilization rate of the command buffer (0…100%).
nBufferMaximumDemandMeter	BYTE	Maximum utilization rate of the command buffer reached so far (0…100%). The counter can be reset via the input bResetMaximumDemandCounter.
nBufferOverflowCounter	UINT	Number of command buffer overflows to date. The counter can be reset via the input bResetOverflowCounter.

Requirements

Development environment	Required PLC library
TwinCAT from v3.1.4024.29	Tc3_DALI from v3.11.0.0