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
$98.15
Apple Inc.
-0.23
MSFT
$43.58
Microsoft Corpora
-0.31
GOOG
$587.42
Google Inc.
+1.81

MacTech Search:
Community Search:

Software Updates via MacUpdate

Knock 1.1.7 - Unlock your Mac by knockin...
Knock is a faster, safer way to sign in. You keep your iPhone with you all the time. Now you can use it as a password. You never have to open the app -- just knock on your phone twice, even when it's... Read more
Mellel 3.3.6 - Powerful word processor w...
Mellel is the leading word processor for OS X and has been widely considered the industry standard since its inception. Mellel focuses on writers and scholars for technical writing and multilingual... Read more
LibreOffice 4.3.0.4 - Free Open Source o...
LibreOffice is an office suite (word processor, spreadsheet, presentations, drawing tool) compatible with other major office suites. The Document Foundation is coordinating development and... Read more
Freeway Pro 7.0 - Drag-and-drop Web desi...
Freeway Pro lets you build websites with speed and precision... without writing a line of code! With it's user-oriented drag-and-drop interface, Freeway Pro helps you piece together the website of... Read more
Drive Genius 3.2.4 - Powerful system uti...
Drive Genius is an OS X utility designed to provide unsurpassed storage management. Featuring an easy-to-use interface, Drive Genius is packed with powerful tools such as a drive optimizer, a... Read more
Vitamin-R 2.15 - 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
Toast Titanium 12.0 - The ultimate media...
Toast Titanium goes way beyond the very basic burning in the Mac OS and iLife software, and sets the standard for burning CDs, DVDs, and now Blu-ray discs on the Mac. Create superior sounding audio... Read more
OS X Yosemite Wallpaper 1.0 - Desktop im...
OS X Yosemite Wallpaper is the gorgeous new background image for Apple's upcoming OS X 10.10 Yosemite. This wallpaper is available for all screen resolutions with a source file that measures 5,418... Read more
Acorn 4.4 - Bitmap image editor. (Demo)
Acorn is a new image editor built with one goal in mind - simplicity. Fast, easy, and fluid, Acorn provides the options you'll need without any overhead. Acorn feels right, and won't drain your bank... Read more
Bartender 1.2.20 - Organize your menu ba...
Bartender lets you organize your menu bar apps. Features: Lets you tidy your menu bar apps how you want. See your menu bar apps when you want. Hide the apps you need to run, but do not need to... Read more

Latest Forum Discussions

See All

Ice Wings Plus (Games)
Ice Wings Plus 1.0 Device: iOS Universal Category: Games Price: $1.99, Version: 1.0 (iTunes) Description: THE GREAT ENDLESS RUNNER OF COMBAT JETS IS BACK !! With more than 680.000 downloads in the App Store, Ice Wings: Skies of Steel... | Read more »
Murl the Squirrel (Games)
Murl the Squirrel 1.0 Device: iOS Universal Category: Games Price: $.99, Version: 1.0 (iTunes) Description: Meet Murl. He is teased by a group of flying squirrels because he can't fly. Determined to show them he's can fly, he meets... | Read more »
Celleste (Games)
Celleste 0.1 Device: iOS Universal Category: Games Price: $2.99, Version: 0.1 (iTunes) Description: Lots of cute action with amazing 3D graphics and a new type of gameplay! Take control over the forces of the universe to help a group... | Read more »
Super Heavy Sword (Games)
Super Heavy Sword 0.0.1 Device: iOS Universal Category: Games Price: $.99, Version: 0.0.1 (iTunes) Description: Get Ready to Get HEAVY! Monster Robot Studios presents SUPER Heavy Sword! The sequel to the smash hit HEAVY sword which... | Read more »
Angels In The Sky (Games)
Angels In The Sky 1.00 Device: iOS Universal Category: Games Price: $6.99, Version: 1.00 (iTunes) Description: - A.I.S will only run smoothly on iPhone 5s. It's NOT compatible with iPad, iPhone 5 or earlier devices.- In order to... | Read more »
80 Days (Games)
80 Days 1.0.2 Device: iOS Universal Category: Games Price: $4.99, Version: 1.0.2 (iTunes) Description: 1872, with a steampunk twist. Phileas Fogg has wagered he can circumnavigate the world in just eighty days. Choose your own route... | Read more »
Micromon (Games)
Micromon 1.0 Device: iOS Universal Category: Games Price: $.99, Version: 1.0 (iTunes) Description: 130+ Animated Monsters to Catch & Battle! No waiting, play at your own pace! Embark on an epic monster capture RPG like none... | Read more »
Empire Manager (Games)
Empire Manager 1.0 Device: iOS iPhone Category: Games Price: $3.99, Version: 1.0 (iTunes) Description: Become ruler of an empire. Manage your economy, develop technology, hire an army and conquer the world in this addictive turn-... | Read more »
Empire Manager HD (Games)
Empire Manager HD 1.0 Device: iOS Universal Category: Games Price: $7.99, Version: 1.0 (iTunes) Description: Become ruler of an empire. Manage your economy, develop technology, hire an army and conquer the world in this addictive... | Read more »
Star Admiral Review
Star Admiral Review By Rob Thomas on July 30th, 2014 Our Rating: :: ADMIRABLE ADMIRALSUniversal App - Designed for iPhone and iPad While this new digital CCG may feel a bit familiar, Star Admiral offers a sci-fi twist and galaxy’s... | Read more »

Price Scanner via MacPrices.net

iPad Cannibalization Threat “Overblown”
Seeking Alpha’s Kevin Greenhalgh observes that while many commentators think Apple’s forthcoming 5.5-inch panel iPhone 6 will cannibalize iPad sales, in his estimation, these concerns are being... Read more
Primate Labs Releases July 2014 MacBook Pro P...
Primate Labs’ John Poole has posted Geekbench 3 results for most of the new MacBook Pro models that Apple released on Tuesday. Poole observes that overall performance improvements for the new MacBook... Read more
Apple Re-Releases Bugfixed MacBook Air EFI Fi...
Apple has posted a bugfixed version EFI Firmware Update 2.9 a for MacBook Air (Mid 2011) models. The update addresses an issue where systems may take longer to wake from sleep than expected, and... Read more
Save $50 on the 2.5GHz Mac mini, plus free sh...
B&H Photo has the 2.5GHz Mac mini on sale for $549.99 including free shipping. That’s $50 off MSRP, and B&H will also include a free copy of Parallels Desktop software. NY sales tax only. Read more
Save up to $140 on an iPad Air with Apple ref...
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
$250 price drop on leftover 15-inch Retina Ma...
B&H Photo has dropped prices on 2013 15″ Retina MacBook Pros by $250 off original MSRP. Shipping is free, and B&H charges NY sales tax only: - 15″ 2.3GHz Retina MacBook Pro: $2249, $250 off... Read more
More iPad Upgrade Musings – The ‘Book Mystiqu...
Much discussed recently, what with Apple reporting iPad sales shrinkage over two consecutive quarters, is that it had apparently been widely assumed that tablet users would follow a two-year hardware... Read more
13-inch 2.5GHz MacBook Pro on sale for $999,...
Best Buy has the 13″ 2.5GHz MacBook Pro available for $999.99 on their online store. Choose free shipping or free instant local store pickup (if available). Their price is $100 off MSRP. Price is... Read more
Save up to $300 on an iMac with Apple refurbi...
The Apple Store has Apple Certified Refurbished iMacs available for up to $300 off the cost of new models. Apple’s one-year warranty is standard, and shipping is free. These are the best prices on... Read more
WaterField Unveils 15″ Outback Solo & 13″...
Hard on the heels of Apple’s refreshed MacBook Pro Retina laptops announcement, WaterField Designs has unveiled a 15-inch version of the waxed-canvas and leather Outback Solo and a 13-inch version of... Read more

Jobs Board

Sr. Product Leader, *Apple* Store Apps - Ap...
**Job Summary** Imagine what you could do here. At Apple , great ideas have a way of becoming great products, services, and customer experiences very quickly. Bring Read more
Sr Software Lead Engineer, *Apple* Online S...
Sr Software Lead Engineer, Apple Online Store Publishing Systems Keywords: Company: Apple Job Code: E3PCAK8MgYYkw Location (City or ZIP): Santa Clara Status: Full Read more
Sr Software Lead Engineer, *Apple* Online S...
Sr Software Lead Engineer, Apple Online Store Publishing Systems Keywords: Company: Apple Job Code: E3PCAK8MgYYkw Location (City or ZIP): Santa Clara Status: Full Read more
*Apple* Solutions Consultant (ASC) - Apple (...
**Job Summary** The ASC is an Apple employee who serves as an Apple brand ambassador and influencer in a Reseller's store. The ASC's role is to grow Apple Read more
Sr. Product Leader, *Apple* Store Apps - Ap...
**Job Summary** Imagine what you could do here. At Apple , great ideas have a way of becoming great products, services, and customer experiences very quickly. Bring Read more
All contents are Copyright 1984-2011 by Xplain Corporation. All rights reserved. Theme designed by Icreon.