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.

 
AAPL
$101.79
Apple Inc.
+0.21
MSFT
$46.68
Microsoft Corpora
+0.16
GOOG
$589.27
Google Inc.
+4.50

MacTech Search:
Community Search:

Software Updates via MacUpdate

Quicken 2015 2.0.4 - Complete personal f...
Quicken 2015 helps you manage all your personal finances in one place, so you can see where you're spending and where you can save. Quicken automatically categorizes your financial transactions,... Read more
iMazing 1.0 - Complete iOS device manage...
iMazing (formerly DiskAid) is the ultimate iOS device manager with capabilities far beyond what iTunes offers. With iMazing and your iOS device (iPhone, iPad, or iPod), you can: Copy music to and... Read more
Xcode 6.0.1 - Integrated development env...
Apple Xcode is Apple Computer's integrated development environment (IDE) for OS X. The full Xcode package is free to ADC members and includes all the tools you need to create, debug, and optimize... Read more
Apple Safari 7.1 - Apple's Web brow...
Apple Safari in OS X Mavericks brings you all-new ways to find and enjoy the best of the web. It works with iCloud to give you a seamless browsing experience across all your devices. It looks out for... Read more
Delivery Status 6.1.2 - Check delivery s...
Delivery Status displays delivery status of packages for a variety of shipment services. Can't wait for your packages to arrive? Don't waste your time checking the site constantly, just open this all... Read more
Mavericks Cache Cleaner 8.0.9 - Clear ca...
Mavericks Cache Cleaner is an award-winning general purpose tool for OS X. MCC makes system maintenance simple with an easy point-and-click interface to many OS X functions. Novice and expert users... Read more
OneNote 15.2.2 - Free digital notebook f...
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
Apple Configurator 1.6 - Configure and d...
Apple Configurator makes it easy for anyone to mass configure and deploy iPhone, iPad, and iPod touch in a school, business, or institution. Three simple workflows let you prepare new iOS devices... Read more
SpamSieve 2.9.16 - Robust spam filter fo...
SpamSieve is a robust spam filter for major email clients that uses powerful Bayesian spam filtering. SpamSieve understands what your spam looks like in order to block it all, but also learns what... Read more
OS X Server 3.2.1 - For OS X 10.9.5 Mave...
OS X Server is the next generation of Apple's award winning server software. Designed for OS X and iOS devices, OS X Server makes it easy to share files, schedule meetings, synchronize contacts, host... Read more

Latest Forum Discussions

See All

Huerons (Games)
Huerons 1.1 Device: iOS Universal Category: Games Price: $.99, Version: 1.1 (iTunes) Description: EXCLUSIVE LAUNCH PRICE! Huerons is 50% off until September 20th! Huerons are tiny colored circles. Merge them by clicking on an empty... | Read more »
Down Among the Dead Men (Games)
Down Among the Dead Men 1.0 Device: iOS Universal Category: Games Price: $.99, Version: 1.0 (iTunes) Description: Avast! Take to the high seas in a fully interactive piratical tale of broadsides and buccaneers. From author Dave... | Read more »
Sling Adds Chromecast Support Through Sl...
Sling Adds Chromecast Support Through Slingplaye​r Mobile Apps Posted by Jessica Fisher on September 18th, 2014 [ permalink ] | Read more »
How to Completely Delete Your iPhone’s C...
The iPhone 6 is out tomorrow, and plenty of people are excited about it. So much so that they’re planning to – or already have – traded in their old iPhone to go towards it. The thing about trading in hardware is it’s very important to make sure... | Read more »
Dragon Quest I Review
Dragon Quest I Review By Andrew Fisher on September 18th, 2014 Our Rating: :: THINE QUEST AWAITETHUniversal App - Designed for iPhone and iPad Its historical significance aside, Dragon Quest 1 is a fun, campy, difficult, thoroughly... | Read more »
It Came From Canada: Overkill 3
Overkill 3 is like every trope of big modern gaming rolled into one. It’s a sequel to an action-packed military shooter. It’s flashy and scripted and flaunts its sophisticated graphics. And it’s a mobile game with a heavy emphasis on in-app... | Read more »
New Modes and Leader Boards in Update fo...
New Modes and Leader Boards in Update for Rules! Posted by Jessica Fisher on September 18th, 2014 [ permalink ] Universal App - Designed for iPhone and iPad | Read more »
TwistedRun Review
TwistedRun Review By Rob Thomas on September 18th, 2014 Our Rating: :: DON'T TWIST YOUR ANKLE!Universal App - Designed for iPhone and iPad TwistedRun is kind of like running up a giant curly fry into the sky. Or maybe that was just... | Read more »
Scope Review
Scope Review By Jennifer Allen on September 18th, 2014 Our Rating: :: LOCATION AWAREiPhone App - Designed for the iPhone, compatible with the iPad Want to easily find photos from around the world based on their location? Scope is a... | Read more »
HipstaFox Review
HipstaFox Review By Jordan Minor on September 18th, 2014 Our Rating: :: FANTASTIC MR. FOXUniversal App - Designed for iPhone and iPad HipstaFox is a great single that makes players long for the whole album.   | Read more »

Price Scanner via MacPrices.net

iOS 8 Adoption Rate Slower than iOS 7, 6, Hit...
Apple began pushing out iOS 8 updates to eligible devices around 1pm ET on September 17, 2014. However, unlike with iOS 7, which boasted a wide variety of differences from its predecessor iOS 6, in... Read more
Save up to $300 on the price of a new Mac wit...
Purchase a new Mac or iPad at The Apple Store for Education and take up to $300 off MSRP. All teachers, students, and staff of any educational institution qualify for the discount. Shipping is free,... Read more
13-inch 2.8GHz Retina MacBook Pro available f...
B&H Photo has the new 2014 13″ 2.8GHz Retina MacBook Pro on sale for $1699.99 including free shipping plus NY sales tax only. They’ll also include free copies of Parallels Desktop and LoJack for... Read more
16GB iPad Air on sale for $449, save $50
Walmart has the 16GB iPad Air WiFi on sale for $449 on their online store for a limited time. Choose free home shipping or free local store pickup. Their price represents a $50 savings over standard... Read more
13-inch 256GB MacBook Air on sale for $1099,...
B&H Photo has the 2014 13″ 1.4GHz 256GB MacBook Air on sale for $1099.99. Shipping is free, and B&H charges NY sales tax only. Their price is $100 off MSRP. Read more
Toshiba Introduces TransMemory ID High-Speed...
Toshiba’s Digital Products Division (DPD), a division of Toshiba America Information Systems, Inc., today introduced the TransMemory ID USB 3.0 Flash Drive, a simpler storage solution for people who... Read more
New iPads and OS X Yosemite Release Coming Oc...
The DailyDot’s Micah Singleton reports that Apple is planning to hold its next product announcement event on Oct. 21, at which it will unveil the iPad Air 2 and iPad mini 3 and release a final build... Read more
Logitech Bluetooth Multi-Device Cross-Platfor...
Logitech has an enviable track record of making some of the best computer keyboards and mice. At least in my estimation, the best freestanding keyboards I’ve ever used have been Logitech units,... Read more
Roundup of Apple refurbished iPad Airs and iP...
Apple is offering Certified Refurbished iPad Airs for up to $140 off MSRP. Apple’s one-year warranty is included with each model, and shipping is free. Stock tends to come and go with some of these... Read more
Sprint offers 16GB iPad mini for $199.99 with...
Sprint is offering 1st generation 16GB iPad minis for $199.99 with a 2-year service agreement. Standard MSRP for this iPad is $429. Their price is the lowest available for this model. Read more

Jobs Board

Project Manager, *Apple* Financial Services...
**Job Summary** Apple Financial Services (AFS) offers consumers, businesses and educational institutions ways to finance Apple purchases. We work with national and Read more
*Apple* Retail - Multiple Positions (US) - A...
Sales Specialist - Retail Customer Service and Sales Transform Apple Store visitors into loyal Apple customers. When customers enter the store, you're also the Read more
*Apple* Retail - Multiple Positions (US) - A...
Sales Specialist - Retail Customer Service and Sales Transform Apple Store visitors into loyal Apple customers. When customers enter the store, you're also the Read more
*Apple* Retail - Multiple Positions (US) - A...
Sales Specialist - Retail Customer Service and Sales Transform Apple Store visitors into loyal Apple customers. When customers enter the store, you're also the Read more
*Apple* Retail - Multiple Positions (US) - A...
Sales Specialist - Retail Customer Service and Sales Transform Apple Store visitors into loyal Apple customers. When customers enter the store, you're also the Read more
All contents are Copyright 1984-2011 by Xplain Corporation. All rights reserved. Theme designed by Icreon.