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Inside Macintosh: Networking /

Chapter 10 - Link-Access Protocol (LAP) Manager / Using the LAP Manager

Determining if the LAP Manager Is Installed

Before you issue any calls to the LAP Manager, you should check to determine if the LAP Manager is installed on the node that is running your application. The LAP Manager is implemented beginning with AppleTalk version 53. To determine if the
LAP Manager is installed, you can check the low-memory global variable LAPMgrPtr. However, Apple Computer, Inc. recommends that you use a higher-level method to perform this check, such as the one that the code in Listing 10-1 shows.

Listing 10-1 Checking to determine if the LAP Manager is installed

FUNCTION GestaltAvailable: Boolean;
CONST
   _Gestalt = $A1AD;
BEGIN
   GestaltAvailable := TrapAvailable(_Gestalt);
END;

FUNCTION AppleTalkVersion: Integer;
CONST
   versionRequested = 1;   {version of SysEnvRec}
VAR
   refNum: Integer;
   world: SysEnvRec;
   attrib: LongInt;
BEGIN
   AppleTalkVersion := 0;   {default to no AppleTalk}
   IF OpenDriver('.MPP', refNum) = noErr THEN  
                           {open the AppleTalk driver}
      IF GestaltAvailable THEN
      BEGIN
         IF (Gestalt(gestaltAppleTalkVersion, attrib) = noErr)
            THEN
            AppleTalkVersion := BAND(attrib, $000000FF);
      END
      ELSE {Gestalt or gestaltAppleTalkVersion selector isn't }
            { available.}
         IF SysEnvirons(versionRequested, world) = noErr THEN
            AppleTalkVersion := world.atDrvrVersNum;
END;

FUNCTION LAPMgrExists: Boolean;
BEGIN
   {AppleTalk Phase 2 is AppleTalk version 53 and later}
   LAPMgrExists := (AppleTalkVersion >= 53);
END;

Here is the declaration for the TrapAvailable function that the code in
Listing 10-1 calls:

FUNCTION TrapAvailable (theTrap: Integer): Boolean;
VAR
   tType: TrapType;
BEGIN
   tType := GetTrapType(theTrap);
   IF tType = ToolTrap THEN
   BEGIN
      theTrap := BAND(theTrap, $07FF);
      IF theTrap >= NumToolboxTraps THEN
         theTrap := _Unimplemented, ToolTrap;
END;