TweetFollow Us on Twitter

Access to Traps
Volume Number:1
Issue Number:6
Column Tag:MacPascal

Access to OS traps

By Alan Wootton

MacPascal is a miracle. Although billed as an educational product, and many serious programmers probably regard it as a toy (just as many consider the Mac to be merely a toy), MacPascal can be used to prototype professional software products.

Since MacPascal is not sold and supported as a development tool, a small amount of homework is needed to assemble a useful system. First you will need MacPascal. Second you will need RMaker, the resource compiler that runs on the Mac. For some an assembler is nice. And a 68000 debugger may be needed (I use MacDB by Bill Duvall). Since there is no syntax check on inline procedures, a debugger is useful to check the stack at the start of the call even if you are relatively bad at assembly language. Eventually one needs a compiler. For now all that is available is the Lisa Pascal Workshop. Hopefully, a Mac compiler will become available. For my purposes it is necessary for the compiler to generate native code; this rules out a p-code type of system (SoftTech Pascal won’t do). Last but not least, Inside Macintosh is a must.

MacPascal provides methods to access almost all of the toolbox routines that make the Mac so great. The OS traps, however, are a bit tricky. As Steve Brecher showed us last month in MacTutor with his Advanced Mac’ing column, the undocumented GENERIC procedure is used to call OS traps. However, INLINE can also be used for OS traps, as we shall see this month in this example of using STUFFHEX from Pascal. (See Steve’s Advanced Mac’ing column in this month’s issue for an example of using STUFFHEX from Basic.)

TWO TYPES OF TOOLBOX TRAPS

There are two types of toolbox trap; those that are stack based and those that are register based. The stack based calls are supported using the INLINE procedure. The register based traps, of which most of the OS traps are typical, are more difficult to access because there is no way (other than using GENERIC) to set registers from Pascal. Fortunately, virtually all of the register traps use only D0 and A0. Therefore, if we could set D0 and A0 before the trap and read them afterwards, we would have an OS trap call mechanism using the INLINE procedure. I have written a short piece of 68000 code to accomplish this.

As an example, I have prepared a short program to read the date and time from the system. Two calls are made to the toolbox to do this; both are register based. Note that when a pointer is to be passed in A0, the @ operator must be used to set the variable to the correct value before the call. Also note that for any $A0xx calls that return a value to the calling routine, the flag $100 should be added to not preserve all registers.

GLUE ROUTINE FOR PASCAL TO OS

Our machine language routine will pop from the stack, the addresses of the variables which we wish to place in the registers A0 and D0. We will pop these addresses off the stack and use them to load the variables into the two registers. The new values returned in A0 and D0 will then be copied back into those same two Pascal variables. Note that after the inlineP call, all registers are saved so we can use them any way we please. To return to Pascal, we are using an RTS instruction so it will be necessary for our machine language routine to calculate our return address. Fortunately A0 points at the word before where we must return.

ROUTINE TO LOAD A0 AND D0 FOR OS TRAP CALLS FROM MACPASCAL.

126: 2848 MOVE.L A0,A4   ;SAVE RETURN
128: 548C ADDQ.L #$2,A4  ;POINT TO RET
;
;  get address where trap will go into A0
;
12A: 41FA 000C     LEA   *+$000E,A0
;
;  pop trap from stack and place into code
;
12E: 309F MOVE.W  (A7)+,(A0) 
;
;  get A0 and D0 from stack
;
130: 245F MOVE.L (A7)+,A2 ;POP A0 VAR
132: 265F MOVE.L (A7)+,A3 ;POP D0 VAR
134: 2052 MOVE.L (A2),A0   ;LOAD A0
136: 2013 MOVE.L (A3),D0    ;LOAD D0
;
;  this word gets overwritten by real trap
;
138: FFFF .word  $FFFF  ;do trap now
; 
;  pass back A0 and D0 contents 
;
13A: 2488 MOVE.L A0,(A2) ;SAVE RET A0
13C: 2680 MOVE.L D0,(A3) ;SAVE RET D0
13E: 4ED4 JMP  (A4);RETURN 

We will stuff the machine code for our little OS trap caller above into memory by using the STUFFHEX routine from our Pascal program. The above listing is provided to show how the machine language patch works. Two OS traps, ReadDateTime and Secs2Date will be called using our OS trap caller, returning the information in variables of our DateTime record. From this example, it should be obvious how to access other OS type traps using INLINE procedures. (As we mentioned, the undocumented GENERIC can also be used for this purpose.)

program show_date_time;

{ This is a test of a method of accessing   }
{ the Mac OS toolbox traps from Mac         }
{ Pascal that are register based, using    }
{ A0 and D0 only. The call will be:            }
{inlineP($4E75,@d0, @a0, trap,@access)}
{ d0 and a0 hold values of registers D0      }
{ and A0 before and after the call. Trap   }
{ refers to the trap address being called.}

type
 DaTimRec = record
 year: integer;
 month: integer;
 day: integer;
 hour: integer;
 minute: integer;
 second: integer;
 dayofweek: integer;
 end;

var
 currentTime: DatimRec;

procedure GetTime(var date: DaTimRec);
 var
 access: array[0..12] of integer;
 d0,a0, secs: longint;
begin
 stuffhex(@access,’2848548C41FA000C309F245F265F20522013FFFF248826804ED4');
a0:=ord(@secs);

inlineP($4E75,@d0,@a0,$A139, @access);
{ReadDateTime, pointer to secs in A0}

a0:=ord(@date);

inlineP($4E75,@secs,@a0,$A9C6,@access);
{Secs2Date, secs in d0, pointer to record}
{is in A0.}

end;
begin {main}
 GetTime(currentTime);
 with currentTime do
 begin
 writeln(‘year is’, year);
 writeln(‘month is’, month);
 writeln(‘day is’, day);
 writeln(‘hour is’, hour);
 writeln(‘minute is’, minute);
 writeln(‘second is’, second);
 writeln(‘year is’, year);
 writeln(‘day of week is’, dayofweek);
 end;
end.

 

Community Search:
MacTech Search:

Software Updates via MacUpdate

Adobe Dreamweaver CC 2020 20.1 - Build w...
Dreamweaver CC 2020 is available as part of Adobe Creative Cloud for as little as $20.99/month (or $9.99/month if you're a previous Dreamweaver customer). Adobe Dreamweaver CC 2020 allows you to... Read more
Adobe Audition 13.0.3 - Professional pos...
Audition is available as part of Adobe Creative Cloud for as little as $20.99/month (or $9.99/month if you're a previous Audition customer). Adobe Audition empowers you to create and deliver... Read more
Adobe After Effects 17.0.3 - Create prof...
After Effects is available as part of Adobe Creative Cloud for $52.99/month (or $20.99/month for a single app license). The new, more connected After Effects can make the impossible possible. Get... Read more
Audio Hijack 3.6.4 - Record and enhance...
Audio Hijack (was Audio Hijack Pro) drastically changes the way you use audio on your computer, giving you the freedom to listen to audio when you want and how you want. Record and enhance any audio... Read more
Eye Candy 7.2.3.96 - 30 professional Pho...
Eye Candy renders realistic effects that are difficult or impossible to achieve in Photoshop alone, such as Fire, Chrome, and the new Lightning. Effects like Animal Fur, Smoke, and Reptile Skin are... Read more
Notability 4.2.2 - Note-taking and annot...
Notability is a powerful note-taker to annotate documents, sketch ideas, record lectures, take notes and more. It combines, typing, handwriting, audio recording, and photos so you can create notes... Read more
Adobe Acrobat Reader 20.006.20034 - View...
Adobe Acrobat Reader allows users to view PDF documents. You may not know what a PDF file is, but you've probably come across one at some point. PDF files are used by companies and even the IRS to... Read more
Adobe Acrobat DC 20.006.20034 - Powerful...
Acrobat DC is available only as a part of Adobe Creative Cloud, and can only be installed and/or updated through Adobe's Creative Cloud app. Adobe Acrobat DC with Adobe Document Cloud services is... Read more
Day One 4.8 - Maintain a daily journal.
Day One is an easy, great-looking way to use a journal / diary / text-logging application. Day One is well designed and extremely focused to encourage you to write more through quick Menu Bar entry,... Read more
OmniPlan 3.14 - Professional-grade proje...
With OmniPlan, you can create logical, manageable project plans with Gantt charts, schedules, summaries, milestones, and critical paths. Break down the tasks needed to make your project a success,... Read more

Latest Forum Discussions

See All

Marvel Strike Force introduces new brawl...
FoxNext's squad-based RPG Marvel Strike Force is set to receive some fresh characters from the X-Men and Iron Man series. They'll arrive as part of the game's latest update, which follows a sizable spending boycott on the title due to complaints... | Read more »
Speed Dating for Ghosts is a narrative a...
Speed Dating for Ghosts originally released on Steam back 2018, since then it has received honourable mentions for narrative during the Independent Games Festival. Now it's made its way over to iOS devices where it's available as a premium title... | Read more »
Fast-paced multiplayer title Tennis Star...
Tennis Stars: Ultimate Clash is the latest free-to-play tennis title to hit iOS and Android. It's said to be a fairly casual experience, offering easy-to-learn controls and fast-paced, mobile-friendly matches. [Read more] | Read more »
Super Mecha Champions' latest updat...
Super Mecha Champions' latest update sees the addition of a brand new character called R.E.D. Alongside that, there's news about the current season and a series of Emojis that have been added to the game. [Read more] | Read more »
Isle Escape: The House is an upcoming pu...
Isle Escape: The House is an upcoming puzzle game from Simeon Angelov that's intended to serve as an introduction to a saga they're planning on releasing in an episodic fashion. The first chapter is set to release for both iOS and Android on 29th... | Read more »
Company of Heroes, the classic RTS, is n...
Feral Interactive has finally released their highly anticipated iOS version of the strategy classic Company of Heroes. It's available now for iPad as a premium title and has had various tweaks to ensure that it's optimised for touch controls. [... | Read more »
Mario Kart Tour's Vancouver Tour ha...
With Mario Kart Tour's Valentine's Tour now at an end (suspiciously before Valentine's Day has even arrived), it's now time to move on to the all-new and exciting Vancouver Tour. This time around, the featured drivers are Hiker Wario and Aurora... | Read more »
A new PictoQuest update makes it a much...
PictoQuest is a charming little puzzle game, but it left us a little disappointed. The game just didn’t seem to use screen space effectively, to the point that using the touch controls (as opposed to the default virtual d-pad) could lead to errant... | Read more »
Alley is an atmospheric adventure game a...
Alley is an atmospheric adventure game that sees you playing as a young girl trapped in an inescapable nightmare. Surrounded by her worst fears, every step forward for her is a huge challenge that you'll help guide her through using some simple... | Read more »
Fight monsters and collect heroes in Cry...
From Final Fantasy to Chaos Rings, Japanese roleplaying games have found a large and loyal fanbase on mobile devices. If you’re seeking a more under-the-radar JRPG to escape into, Lionsfilm’s Cryptract could be the one. The game has been around... | Read more »

Price Scanner via MacPrices.net

Save up to $220 on 11″ iPad Pros with these r...
Apple has Certified Refurbished 11″ iPad Pros available on their online store for up to $220 off the cost of new models. Prices start at $679. Each iPad comes with a standard Apple one-year warranty... Read more
8-Core 27″ iMac Pro available for $4249, Cert...
Apple has Certified Refurbished 27″ 3.2GHz 8-Core iMac Pros available for $4249 including free shipping. Their price is $750 off the cost of new models. A standard Apple one-year warranty is included... Read more
$749 MacBook Airs continue to be available on...
Amazon has the 2017 13″ 1.8GHz/128GB MacBook Air on sale today for only $749 shipped. That’s $250 off Apple’s original MSRP for this model and the cheapest new MacBook available from any Apple... Read more
HomePods on sale for $204 at Other World Comp...
Other World Computing has discounted, new, Apple HomePods on sale for up to $95 off Apple’s MSRP: – HomePod Space Gray: $207.99 $92 off MSRP – HomePod White: $204.99 $95 off MSRP These are the same... Read more
Get a Certified Refurbished iMac at Apple for...
Apple has Certified Refurbished 2019 21″ & 27″ iMacs available starting at $929 and up to $350 off the cost of new models. Apple’s one-year warranty is standard, shipping is free, and each iMac... Read more
A Look Back At The Top 5 Most Read Stories Of...
FEATURE: 02.21.20 The best of the best are now history and we’re not talking about Super Bowl LIV from earlier this month but rather, coverage from the past year (its second and first full one at... Read more
Apple offers wide range of discounted custom...
Save up to $610 on a custom-configured 21″ or 27″ iMac with these Certified Refurbished models available at Apple. Each iMac features a new outer case, free shipping, and includes Apple’s standard 1-... Read more
Find the best prices and sales on Macs, iPads...
Our Apple award-winning price trackers are the best place to look for the best New Year’s deals and lowest prices on Apple gear. Scan our price trackers for the latest information on sales, bundles,... Read more
Apple’s 27″ 8-Core iMac Pro on sale today for...
B&H Photo has the base 8-Core 3.2GHz 32GB/1TB iMac Pro on sale today for $4599 — $400 off Apple’s MSRP. Overnight shipping is free to many addresses in the US: – 8-Core 3.2GHz 32GB/1TB iMac Pro... Read more
In stock! Apple’s new Mac Pro for $5995 with...
Apple reseller DataVision has the new 2019 Apple Mac Pro in stock today for $5995 ($5 off MSRP) including free shipping. DataVision charges sales tax for NY, NJ, PA, and CA residents only. If you don... Read more

Jobs Board

Medical Assistant - *Apple* Valley Clinic -...
…professional, quality care to patients in the ambulatory setting at the M Health Fairview Apple Valley Clinic, located in Apple Valley, MN. Join the **M Health Read more
Geek Squad *Apple* Consultation Professiona...
**756636BR** **Job Title:** Geek Squad Apple Consultation Professional **Job Category:** Store Associates **Store NUmber or Department:** 001053-Arundel Mills-Store Read more
Medical Assistant - *Apple* Valley Clinic -...
…professional, quality care to patients in the ambulatory setting at the M Health Fairview Apple Valley Clinic, located in Apple Valley, MN. Join the **M Health Read more
*Apple* Certified Repair Technician - Utah S...
…selected candidate will work in the USU Campus Store Tech Department as an Apple Certified Repair Technician and floor associate. This position is for both summer Read more
*Apple* Mobility Pro - Best Buy (United Stat...
**744429BR** **Job Title:** Apple Mobility Pro **Job Category:** Store Associates **Store NUmber or Department:** 000574-Garner-Store **Job Description:** At Best Read more
All contents are Copyright 1984-2011 by Xplain Corporation. All rights reserved. Theme designed by Icreon.