TweetFollow Us on Twitter

MDS->MPW
Volume Number:5
Issue Number:6
Column Tag:Developer Notes

MDS->MPW

By Dan Weston, Portland, OR

Converting MDS files to MPW

This article describes how to convert MDS assembler source files to the MPW environment. I don’t go into all the details, but try and give you enough of the major points so that you can get your old files over to MPW and get more productive. MPW is a very rich and wonderful environment and I am purposely ignoring many of its subtle and not-so-subtle features in this article for the sake of clarity (and deadline).

Declare a MAIN Procedure

MPW expects you to declare at least one code module in your source file. There are several ways to start a code module, but the easiest is to put the MAIN directive on the same line at the label at the start of your code producing statements. For example, the following code fragment establishes the label “Start” and the main code module.

Start MAIN; code statements start here

If you don’t declare a code module, either by using MAIN or PROC or FUNC, MPW will complain heartily.

Declare Global Data Record

In MDS, it is customary to declare global variables with the DS directive. The MDS assembler gathers all DS directives together into a common global data block and tells the linker to locate the data block at -256(a5) when the program is loaded. (This location is the default and you can change it with Link directives, although most people don’t bother to change it. Later in this article when we discuss the QuickDraw globals, you will see that the location of the application globals in MDS is important.) All the labels associated with the DS statements become negative offsets from A5 to the proper location in the data area. For example, if you have the following data statements in your MDS file:

thePointds.l1  ;space for a Point
theRect ds.w4  ;4 words for a Rect

You can access those variables by using the name of the variable as an offset from register a5, as in this line of code.

  move.l   thePoint(a5),-(sp) 

In MDS files, DS directives can be placed anywhere in the file, and the assembler will gather them all together and make a single data block. The MPW assembler also gathers up DS statements and makes code modules and the MPW linker combines all the data modules and place them just below the a5 boundary points when the program is loaded. The MPW linker does not give you an automatic 256 byte cushion below the a5 boundary the way the MDS linker does. Labels for DS statements become negative offsets from register a5, however, in much the same way as in MDS. You can access MPW assembler data variables by using the variable name (label) as as offset from register a5, as shown in the previous example.

A better way to declare global variables in MPW is to gather all your DS statements together into a RECORD and then use that data template to access all your globals as fields of the template. For example, to convert the global variables from the MDS example above, you would place the following data declaration at the beginning of your file (after the ‘INCLUDES’ and ‘EQU’ statements but before the first code statements).

MyData RECORD

thePoint ds.l 1

theRect ds.w 4

ENDR

Once you declare a block of globals this way, you can access the individual variables without referencing register a5, since the MPW assembler will automatically generate the ar reference for you. You access a variable by using its data module name ( eg. ‘MyData’) and a field name from the data template (eg. ‘thePoint’), much like a record structure in C or Pascal. For example, you can access the variable at the label ‘thePoint’ with the following code.

    move.l   MyData.thePoint,-(sp)  

You can also declare implicit data modules by using the WITH directive. For example, if you preceded the previous example with the statement:

Start MAIN
 WITH   MyData
 ; Code statements begin here

you could dispense with the data module name when accessing individual fields of the data module, so that the access statement becomes:

    move.l   thePoint,-(sp)  

In summary then; when converting an MDS file to MPW, gather all your DS directive lines into a single data module and give the data module name (the label that appears on the same line as the RECORD directive) in a WITH statement before accessing any of the variables in the data module. You can then access the variables by using their names without worrying about referencing register a5.

Declare QuickDraw Globals

One of the hidden features of the MDS linker is that it places the application globals 256 bytes below the a5 boundary by default. The MPW linker places the application globals right below the a5 boundary, without any cushion. Most casual assembly language programmers (is there such a thing?) just accept the default and don’t really think about it, but it can get you in a lot of trouble when converting between MDS and MPW if you don’t take this difference into account.

In particular, it is common for MDS programs to assume that the QuickDraw globals will be placed just below the a5 boundary, extending downward in memory for 206 bytes. The ROM call InitGraf expects a pointer to the 203rd byte of a 206 byte area for the QuickDraw globals. Because MDS gives a 256 byte cushion below the a5 boundary before the application’s globals, MDS programs typically call InitGraf with a pointer to a long word four bytes below the a5 boundary, as shown below.

; typical MDS technique
 pea    -4(a5)   
 _InitGraf

This works great in MDS programs because the QuickDraw globals grow downward from the a5 boundary but are not large enough to outgrow the 256 byte cushion provided by the MDS linker.

In MPW, you are not so lucky. You must explicitly allocate some global storage for the Quickdraw globals in a data module and then pass a pointer to that module when calling InitGraf. If you don’t do this and use the previous code to initialize QuickDraw, your globals and the QuickDraw globals will share overlapping data space beneath the a5 boundary, and that will cause your program to crash as your program and QuickDraw write over each others globals.

The sample program provided with MPW shows a good method for allocating data space for the QuickDraw globals. Listed below is a simplified version of that method. First, declare a data module for the QD globals. This declaration should come just before or just after your application’s data declaration, but before any code statements, as shown below.

QDGlobals RECORD ,DECREMENT

thePort DS.L 1

white DS.B 8

black DS.B 8

gray DS.B 8

ltGray DS.B 8

dkGray DS.B 8

arrow DS.B cursRec

screenBits DS.B bitmapRec

randSeed DS.L 1

ORG -grafSize

ENDR

Once the QD globals data module is declared, it will be combined with any other data modules in your program and loaded just below the a5 boundary when the program is loaded. Because you don’t know exactly where the QD globals will be loaded in relation to the other data modules (alright, if you dig through the MPW manuals you can probably figure out how the data modules are ordered).

In order to use the QuickDraw globals that are defined as a data module, you should place the name of the data module in the WITH directive along with the name of your application’s data module, as shown below.

Start MAIN
 WITH   MyData,QDGlobals

 ; Code statements begin here

And, once you are using the QD globals you have defined, you can point directly to the QD data area when initializing QuickDraw, as shown below.

; thePort is a variable in QDGlobals
 pea    thePort  
 _InitGraf

By explicitly defining a data area for the QuickDraw globals and pointing to it when initializing QuickDraw you can avoid the data overlap that occurs when you convert an MDS program without thinking about the details.

Misc Details

-- MPW uses IMPORT and EXPORT instead of the XDEF and XREF directives found in MDS.

-- Macros are defined differently in MPW and MDS. For example, take a look at the following macro defined for both MDS and MPW:

MDS macro:

 MACRO   _SFGetFile =
 MOVE.W #2,-(SP)
 _Pack3
 |

MPW equivalent macro:

 MACRO   
 _SFGetFile 
 MOVE.W #2,-(SP)
 _Pack3
 ENDM

-- The labels used with EQU and SET statements in MPW must be in the first column, unlike MDS.

-- RMaker and rez source files are totally incompatable, but you use your old resource files by either “including” them in your rez file or running derez on them to get a rez compatable source file.

-- Make files made by the “Create Build Commands...” menu option in MPW typically are a good way to build your programs, but you can remove the link files “Runtime.o” and “Interface.o” put in the make file by default.

 

Community Search:
MacTech Search:

Software Updates via MacUpdate

Sparkle Pro 2.8.10 - Visual website crea...
Sparkle Pro will change your mind if you thought building websites wasn't for you. Sparkle is the intuitive site builder that lets you create sites for your online portfolio, team or band pages, or... Read more
WhatsApp 0.4.930 - Desktop client for Wh...
WhatsApp is the desktop client for WhatsApp Messenger, a cross-platform mobile messaging app which allows you to exchange messages without having to pay for SMS. WhatsApp Messenger is available for... Read more
DaisyDisk 4.9 - $9.99
DaisyDisk allows you to visualize your disk usage and free up disk space by quickly finding and deleting big unused files. The program scans your disk and displays its content as a sector diagram... Read more
MacJournal 6.2.2 - $39.95
MacJournal is the world's most popular journaling software for the Mac. MacJournal 6 adds a calendar mode that show entries from any journal, geolocation, word count, and progress tracking, as well... Read more
Vitamin-R 3.14 - Personal productivity t...
Vitamin-R creates the optimal conditions for your brain to work at its best by structuring your work into short bursts of distraction-free, highly focused activity alternating with opportunities for... Read more
Vivaldi 2.11.1811.38 - An advanced brows...
Vivaldi is a browser for our friends. We live in our browsers. Choose one that has the features you need, a style that fits and values you can stand by. From the look and feel, to how you interact... Read more
SteerMouse 5.4.4 - Powerful third-party...
SteerMouse is an advanced driver for USB and Bluetooth mice. SteerMouse can assign various functions to buttons that Apple's software does not allow, including double-clicks, modifier clicks,... Read more
Microsoft OneNote 16.34 - Free digital n...
OneNote is your very own digital notebook. With OneNote, you can capture that flash of genius, that moment of inspiration, or that list of errands that's too important to forget. Whether you're at... Read more
Amadeus Pro 2.7.3 - Multitrack sound rec...
Amadeus Pro lets you use your Mac for any audio-related task, such as live audio recording, digitizing tapes and records, converting between a variety of sound formats, etc. Thanks to its outstanding... Read more
Smultron 12.0.7 - Easy-to-use, powerful...
Smultron 12 is the text editor for all of us. Smultron is powerful and confident without being complicated. Its elegance and simplicity helps everyone being creative and to write and edit all sorts... Read more

Latest Forum Discussions

See All

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 »
Circuit Dude is a top-down, tile-based p...
Circuit Dude is a tile-based puzzler that was originally released on Steam back in 2017. Now it's made it's way over to mobile devices where it's available for both iOS and Android as a premium game. [Read more] | Read more »
Liege Dragon is another upcoming RPG for...
Liege Dragon is an upcoming RPG from Kemco, who has certainly streamlined the process of making their particular brand retro-inspired turn-based games at this point. Liege Dragon will be available for both iOS and Android. [Read more] | Read more »
Hidden Survivor from Joy Brick is a hide...
Joy Brick's Hidden Survivor is an interesting title of two halves: part story-focused survival experience, part intense hide-and-seek multiplayer game. Both elements come together to form a compellingly strange and enjoyable whole. The hide-and-... | Read more »
Stupid Zombies 4 is an upcoming trick-sh...
The Stupid Zombies are preparing to make their grand return to iOS and Android in the fourth instalment of the hugely popular trick-shot shooter series. If you missed out on the earlier games, the basic idea is that you have to bounce bullets... | Read more »

Price Scanner via MacPrices.net

Apple offers 2019 13″ MacBook Pros for up to...
Apple has a full line of Certified Refurbished 2019 13″ 2.4GHz 4-Core Touch Bar MacBook Pros available starting at $1529 and up to $300 off MSRP. Apple’s one-year warranty is included, shipping is... Read more
Save up to $200 on a 13″ MacBook Air at Apple...
Apple has a full line of Certified Refurbished 2019 13″ MacBook Airs available starting at only $929 and up to $200 off the cost of new Airs. Each MacBook features a new outer case, comes with a... Read more
Xfinity Mobile offers iPhone XS models for $3...
Take $300 off the purchase of any Apple iPhone XS model at Xfinity Mobile with a new line activation and transfer of phone number to Xfinity Mobile: – 64GB iPhone XS: $599.99 save $300 – 256GB iPhone... Read more
Apple Watch Series 5 on sale for up to $45 of...
Amazon has Apple Watch Series 5 models available for up to $45 off Apple’s MSRP. Shipping is free. These are the same Apple Watch models sold by Apple in their retail and online stores, and Amazon’s... Read more
Discounted custom iMac Pros available at Appl...
Save up to $1640 on a custom-configured 27″ iMac Pro with these Certified Refurbished models now available at Apple. Each iMac Pro features a new outer case, free shipping, and includes Apple’s... Read more
New at US Cellular: Switch and get a free iPh...
US Cellular has introduced a new deal offering free Apple iPhone 11 smartphones to customers opening a new line of service. No trade-in required, and discounts are applied via monthly bill credit... Read more
President’s Day sale serves up 13″ 2.4GHz Mac...
Apple resellers have 13″ 2.4GHz MacBook Pros on sale up to $300 off Apple’s MSRP as part of their President’s Day sales, and some are including free overnight delivery: (1) Amazon has new 2019 13″ 2.... Read more
President’s Day sale: 16″ MacBook Pros for $3...
B&H Photo has new 16″ MacBook Pros for $300 off Apple’s MSRP, starting at $2099, as part of their President’s Day 2020 sale. Their prices are the cheapest available for 16″ MacBook Pros from any... Read more
Sunday sale: 27″ 5K iMacs for $150 off Apple’...
B&H Photo has new 2019 27″ 5K iMacs in stock today and on sale for $150 off Apple’s MSRP. Overnight shipping is free to many locations in the US: – 27″ 3.0GHz 5K iMac: $1649.99 $150 off MSRP – 27... Read more
Sunday sale: 21″ iMacs for $100-$150 off Appl...
B&H Photo has new 21″ Apple iMacs on sale for $100 off MSRP with models available starting at $999. These are the same iMacs offered by Apple in their retail and online stores. Overnight shipping... Read more

Jobs Board

Hair Stylist - *Apple* Blossom Mall - JCPen...
Hair Stylist - Apple Blossom Mall Location:Winchester, VA, United States- Apple Blossom Mall 1850 Apple Blossom Dr Job ID:1065040Salon Professionals Job Read more
Clinic Health Guide - *Apple* Valley &...
…M Health Fairview has an exciting opportunity for a Clinic Health Guide for its Apple Valley and Farmington clinic locations. As a member of the care team, the Read more
Medical Assistant - *Apple* Valley Clinic -...
…provide professional, quality care to patients in the ambulatory setting at the Fairview Apple Valley Clinic, located in Apple Valley, MN. Join the **Fairview Read more
*Apple* Computing Professional - Best Buy (U...
**757550BR** **Job Title:** Apple Computing Professional **Job Category:** Store Associates **Store NUmber or Department:** 001142-South Loop-Store **Job 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.