Example: Memory ring FiFo (FB_MemRingBuffer)

The interface of the FB_Data setFifo function block:

The application-specific function block FB_Data setFifo used in the project example uses the FB_MemRingBuffer function block internally. This block simplifies adding/removing of data sets. In addition, the new function block provides the current percentage fill status of the buffer and an overwrite option. If the bOverwrite input is set and the buffer is full, the oldest entry is removed from the buffer and overwritten with the new one.

VAR_GLOBAL CONSTANT
    MAX_BUFFER_SIZE : UDINT := 1000;
END_VAR

FUNCTION_BLOCK FB_DataSetFifo
VAR_INPUT
    bOverwrite : BOOL;
    in         : ST_DataSetEntry;
END_VAR
VAR_OUTPUT
    bOk        : BOOL;
    nCount     : UDINT;
    nLoad      : UDINT;
    out        : ST_DataSetEntry;
END_VAR
VAR
    arrBuffer  : ARRAY[0..MAX_BUFFER_SIZE] OF BYTE; (* Buffer memory used by FB_MemRingBuffer function block *)
    fbBuffer   : FB_MemRingBuffer;
END_VAR

The main program:

A rising edge at bReset deletes all buffer entries. If you set bAdd = TRUE a new data record will be written into the ring buffer, and when bRemove =TRUE the oldest data record is removed. A rising edge at bGet results in the oldest data set to be read but not removed.

PROGRAM MAIN
VAR
    fbFifo      : FB_DataSetFifo := ( bOverwrite := TRUE );
    newEntry    : ST_DataSetEntry;
    oldEntry    : ST_DataSetEntry;
    bSuccess    : BOOL;
    nCount      : UDINT;
    nLoad       : UDINT;

    bReset      : BOOL := TRUE;
    bAdd        : BOOL := TRUE;
    bGet        : BOOL := TRUE;
    bRemove     : BOOL := TRUE;
END_VAR

IF bReset THEN
    bReset := FALSE;
    (* reset fifo (clear all entries) *)
    fbFifo.A_Reset( in := newEntry, bOk=>bSuccess, nCount=> nCount, nLoad => nLoad );
END_IF

IF bAdd THEN
    bAdd := FALSE;

    (* create new or modify data set entry *)
    newEntry.bFlag  := NOT newEntry.bFlag;
    newEntry.nValue := newEntry.nValue + 1;
    newEntry.sMsg   := BYTE_TO_STRING(newEntry.nValue);

    (* add new entry to the fifo *)
    fbFifo.A_Add( in := newEntry, bOk=>bSuccess, nCount=> nCount, nLoad => nLoad );
END_IF

IF bGet THEN
    bGet := FALSE;
    (* get (but not delete) oldest entry *)
    fbFifo.A_Get( out => oldEntry, bOk => bSuccess, nCount => nCount, nLoad => nLoad );
END_IF

IF bRemove THEN
    bRemove:= FALSE;
    (* remove oldest entry *)
    fbFifo.A_Remove( out => oldEntry, bOk => bSuccess, nCount => nCount, nLoad => nLoad );
END_IF

Requirements