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CountADBs and Reality

By Donald Koscheka, , Mark Armstrong

This column strives to present interesting insights into enhancing Hypercard through XCMDs. When I started writing this column almost two years ago, I was apprehensive; how would I come up with a new idea each month year in and year out. The answer to this question was something of a revelation to me -- once I decided to keep coming up with new ideas, I began looking in new places for those ideas. No part of Macintosh programming is off-limits, I explore everything. Of course there are limits to what one person can do and I find myself very often writing a column in response to some question asked by a colleague or a reader.

I’ve decided that it’s time to go one step further. Beginning this month, intermittently offer this space for “guest XCMDs” such as Mark Armstrong’s following ADB externals. The guest columnist idea appeals to me for two reasons: (1) it broadens the column’s “reach” by discussing areas that I may have not explored myself and (2) it provides you with different perspectives and coding styles so that you can see how others have solved specific problems in an XCMD. This is an open invitation. If you would like to have your XCMD published, send it to me via AppleLink (N0735) or America OnLine (AFC Donald) or to the Editor. Use Macwrite or TEXT only. I will respond as quickly as possible to inform you as to whether I can use the article or not. A few rules: If I can use the material, I will edit it and return it to you for approval. I edit for style and grammar, expect to have some work done to your prose. Don’t submit anything that you don’t want in the public domain and don’t submit any article without source code. You may use whatever language you like. Give yourself a “short plug” at the beginning of the column so that other readers get to know you better.

This month, I would like to introduce Mark Armstrong, Vice President of Research and Development at Pharos Technologies, Inc, a software development and systems integration company in Cincinnati, Ohio. Mark has written one commercial engineering application on the Macintosh called “UNITize” and has contributed to the arcade-style game “Marble Madness”. With his physics degree firmly in hand, he still wonders how he got mixed up in all this.

CountADBs and Reality

In some circumstances (such as on the factory floor), there is a need to monitor the Macintosh to determine whether the mouse or keyboard devices become detached from ADB. Some software may modify their behavior if certain input devices are available, hiding or showing functionality based on that result. Below are two simple XFCN’s, developed in Think C 4.0, that tell you if the mouse and keyboard are connected.

According to Inside Macintosh Volume 5, the function CountADBs() “returns a value representing the number of devices connected to the Apple Desktop Bus (ADB) by counting the number of entries in the device table....” The important word is representing. It does not really tell you what is connected out there on the bus. Consequently, even if you have no devices hooked up to ADB, CountADBs() will return a value of 2. This happens because the system always installs the keyboard and mouse drivers regardless of whether they are physically resident. To find out what is really connected to ADB you can poll devices that you believe are connected to the ADB. Connected devices will respond to the poll.

Before going too far, you must determine whether the host machine is equipped for ADB. The following call to SysEnvirons() determines whether ADB is installed.

/* 1 */

Boolean ADBExists()
 {
 SysEnvRectheWorld;
 OSErr  err;
 
 err = SysEnvirons(1,&theWorld);
 if (err) return (FALSE);
 else
 {
if ((theWorld.machineType >= 0) && (theWorld.machineType < 3)) 
 return (FALSE);
 else return (TRUE);
 }
 }

Once you have determined that ADB exists on your machine, you check to see what devices are actually there by looping from 1 to the maximum allowable number of ADB devices (16). Inside the loop, you call ADBIndAvail() which returns TRUE if the specified device is physically connected and functional or FALSE otherwise. ADBIndAvail() takes a device specified by the index and sends a command via ADBOp() to that device to see if it is responding. If the device receives the operation, it will signal that it has done so by executing a completion routine. If the completion routine ADBOp() doesn’t execute, then the device did not receive the message, and we can assume that the device is dysfunctional or disconnected. The completion routine ADBComplete() sets a global variable to TRUE. If completion does not occur, then the operation times out and the global variable remains FALSE. In the following code, we use the first byte of Scratch8 as the global variable. We chose to use Scratch8 because this code was developed for a Think C 4.0 XCMD where A4 had already been pushed using SetUpA4(). In most cases, a regular global variable will do the trick.

/* 2 */

#define ADB_TIMEOUT10000

extern char Scratch8[]  : 0x9FA;

ADBComplete(){
 *(char *)Scratch8 = TRUE;
}

ADBIndAvail(index)
 short  index;
 {
 ADBAddress addrs;
 ADBDataBlock  devBlock;
 OSErr  err;
 short  cmdNum;
 Str255 ADBData;
 
 addrs = GetIndADB(&devBlock,index);
 cmdNum = ((addrs*16)+0xF);
 ADBData[0] = 0;
 ADBData[1] = 0;
 ADBData[2] = 0;
 
 *(char *)Scratch8 = FALSE;
 err = ADBOp(NIL,ADBComplete,&ADBData,cmdNum);
 if (!err){
 short I= 0;
 do
 if (++I > ADB_TIMEOUT) *(char *)Scratch8 = TRUE; 
 while (!*(char *)Scratch8);
 if (ADBData[0] != 0) return (TRUE);
 }
 return (FALSE);
}

In both cases below, the first portion of the code checks to see if the first and only argument is a question mark (?) or an exclamation point (!). If so, the XFCN responds appropriately as suggested by MacDTS.

The XFCN checks first to see if ADB exists on this machine and returns an error code if it does not. Next, it loops through all the devices to see if any one of them is a responding mouse. If it finds one, it returns TRUE, otherwise it completes the loop and returns FALSE. Each time through the loop, we call GetIndADB(), as directed in Inside Mac, to determine if the device in question is, indeed, a mouse.

/* 3 */

#include “MacTypes.h”
#include “HyperXCmd.h”
#include “DeskBus.h”
#include “SetUpA4.h”

#define ADB_KEYBOARD 2
#define ADB_MOUSE3

#define STANDARD_KBD 1
#define EXTENDED_KBD 2

#define MAX_ADB_DEVICES 16

pascal main(paramPtr)
   XCmdBlockPtr  paramPtr;
   {
   Str255 str;
   shortix;
   
   RememberA0();
   SetUpA4();
   
   if(paramPtr->paramCount == 1){
   ZeroToPas(paramPtr,*((unsigned char **)paramPtr->params[0]),str);
      if (str[0] == 1){
        if (str[1] == ‘?’) 
 pstrcpy(str,”\pKBDAvail()”);
        else if (str[1] == ‘!’) 
 pstrcpy(str,”\pv1.0; © Pharos Technologies, Inc. 1989");
      }
      goto Done;
   }
   
   if (!ADBExists()){ 
 pstrcpy(str,”\p0\rnoADB”); 
 goto Done; 
 }
   
 for ( ix  =1; ix <=MAX_ADB_DEVICES; ix ++){
 ADBDataBlock    ADBinfo;
 ADBAddress ADBaddr;
 
 if (!ADBIndAvail( ix )) continue;
 ADBaddr = GetIndADB(&ADBinfo,I);
 if (ADBaddr <= 0) continue;
 if (ADBinfo.origADBAddr == ADB_MOUSE){ 
 pstrcpy(str,”\ptrue”); 
 goto Done; 
 }
 }
 pstrcpy(str,”\pfalse”);
Done:
   paramPtr->returnValue = PasToZero(paramPtr,(StringPtr)str);
   RestoreA4();
}

A similar routine checks for keyboard devices. This routine not only checks to see if it is a keyboard, but also returns the type of keyboard by examining the devType field of ADBInfo.

/* 4 */

#include “MacTypes.h”
#include “HyperXCmd.h”
#include “DeskBus.h”
#include “SetUpA4.h”

#define ADB_KEYBOARD 2
#define ADB_MOUSE3
#define STANDARD_KBD 1
#define EXTENDED_KBD 2
#define MAX_ADB_DEVICES 16

pascal main(paramPtr)
   XCmdBlockPtr  paramPtr;
   {
   Str255 str;
   shortI;
   
   RememberA0();
   SetUpA4();
   
   if (paramPtr->paramCount == 1){
   ZeroToPas(paramPtr,*((unsigned char **)paramPtr->params[0]),str);
      if (str[0] == 1){
        if (str[1] == ‘?’) 
 pstrcpy(str,”\pKBDAvail()”);
        else if (str[1] == ‘!’) 
 pstrcpy(str,”\pv1.0; © Pharos Technologies, Inc. 1989");
      }
      goto Done;
    }
   
   if (!ADBExists()){ 
 pstrcpy(str,”\p0\rnoADB”); 
 goto Done; 
 }
   
 for (I=1;I<=MAX_ADB_DEVICES;I++){
 ADBDataBlock    ADBinfo;
 ADBAddress ADBaddr;
 
 if (!ADBIndAvail(I)) continue;
 ADBaddr = GetIndADB(&ADBinfo,I);
 if (ADBaddr <= 0) continue;

 if (ADBinfo.origADBAddr == ADB_KEYBOARD){
 if (ADBinfo.devType == STANDARD_KBD){ 
 pstrcpy(str,”\ptrue,standard”); 
 goto Done; 
 }
 else if (ADBinfo.devType == EXTENDED_KBD){ 
 pstrcpy(str,”\ptrue,extended”); 
 goto Done; 
 }
 else{ 
 pstrcpy(str,”\ptrue,unknown”); 
 goto Done; 
 }
 }
 }
 pstrcpy(str,”\pfalse”);
Done:
   paramPtr->returnValue = PasToZero(paramPtr,(StringPtr)str);
   RestoreA4();
   }

Once you know how to identify a particular device, it is easy to check to see if it is present on ADB. If you don’t know how to identify a given device, then the code above can be easily modified to return all devices found on ADB. By the way, I would like to give special thanks and credit to Cameron Birse. If you don’t recognize the name from any number of “sources”, then never mind.