TweetFollow Us on Twitter

Apr 94 Tips
Volume Number:10
Issue Number:4
Column Tag:Tips & Tidbits

Tips & Tidbits

Edited by Scott Boyd, Editor

Note: Source code files accompanying article are located on MacTech CD-ROM or source code disks.

Tip Of The Month

MPW C Navigation Time Saver

MPW has a nice feature for C programmers: Using the tool CMarker, you can make a list of marks for all the functions in a source file.

Unfortunately, when you open the Mark menu, you can wind up with something unusable. For example, the list could be so long that it takes too much time to find what you’re looking for. Moreover, you are often looking for a function because you are in a piece of code in which you see it being called. It’s right there in front of you. It would be nice to be able to use that piece of context to get you to the function itself.

The following MPW Shell statement sets up a function key which jumps to a function when you highlight its name and press control-enter (or any other key you wish).


/* 1 */
setkey control-enter 'find `catenate "{Active}".§`"{Active}"'

Be sure to get all of the quotes right. MPW cares about the different quotes. Reading from left-to-right, the quotes are straight-, back-, double-, double-, back-, double-, double-, and single-quotes. The § character is option-6.

- Manuel Carlos Alcoba

Informacion, Integracion, Inteligencia

Madrid, Spain

This column is your opportunity to spread the word about little bits of information that you find out about. These tidbits can be programming related or they can be user tips that are particularly useful to programmers.

MacTech Magazine will pay $25 for every tip used, and $50 for the Tip of the Month. Or you can take your award in orders or subscriptions.

To submit a tip, send in a letter to the magazine. E-mail is our preferred method, but feel free to send something via the US Mail. See page two for all addresses. If you do send snail mail, enclose a printed copy and a disk copy of the letter so that it does not have to be retyped.

INLINE ASSEMBLY IN PASCAL

Knowing how to write inline assembly within your pascal code can sometimes save you time and trouble. For example, I use an Inline routine that returns the current stack address for debugging purposes. The routine looks like this:

 
/* 2 */
INTERFACE
  FUNCTION GetStackTop: LongInt; INLINE
   $2E8F;
My code calls it just as if it were a regular function:
VAR
 stackAddress: LongInt;
...
stackAddress := GetStackTop;

When used properly, Inline assembly provides considerable speed improvements and allows you to enhance your Pascal code in ways not possible with straight Pascal.

Define your inline routines in the INTERFACE part of a file. In my example, the hexadecimal number $2E8F represents the instruction MOVE.L A7,(A7). The compiler places this instruction directly into the code. This reduces the number of instructions needed to write and compile this routine in assembly language and also avoids calling overhead for a function. No calling overhead simply means no JSR instructions are generated in the code. When I was learning how to write inline assembly, the biggest obstacle was lack of documentation on how to obtain the hexadecimal format (e.g. $2E8F) of assembly language instructions. You can laboriously try to compose the hexadecimal instruction from some 68000 assembly books, but this usually takes several minutes, is error prone, and requires that you know exactly what you are doing. There is a much easier way to obtain the hexadecimal format of any assembly language instruction, provided you have MPW assembler. This is what you need to do:

Suppose you want to find the hexadecimal format of the MOVE.L A7,(A7) instruction.

1) In MPW, create a new file called Example.a and enter the text:

/* 3 */
RoutineName PROC
 MOVE.L A7,(A7)
 END

2) Create a ‘.o’ file with the MPW ASM tool. In this case I call the file Example.a and the ASM tool creates an Example.a.o file:

/* 4 */
 Asm Example.a

3) Now disassemble the Example.a.o file with the dumpObj MPW tool. The dumpObj takes whatever is inside a compiled file and disassembles it back into assembly language instructions. In this case it disassembles the file Example.a.o into a file called Example.o.a:

/* 5 */
dumpobj 'Example.a.o' > 'Example.o.a'

4) The disassembled file contains the line

/* 6 */
00000000: 2E8F           '..'              MOVE.L     A7,(A7)

The second number on that line, “i.e. 2E8F”, is the hexadecimal format of the assembly instruction.

From now on, anytime you need a hexadecimal format of an instruction, just add the instruction to Example.a file and execute the ASM and dumpObj MPW tools. After you do this a couple of times you will realize this is a simple repetitious process. This usually takes less than a minute and is much easier and quicker than finding the instruction from a book.

- Marek Hajek

Champaign, Illinois

Another hex-for-opcode trick

Finding the hex for an instruction can be useful in a number of situations. One situation I’ve found myself in is sitting in Macsbug on a machine and needing to change a single instruction. For example, suppose Igot a branch condition backwards, and want to change the sense of the conditional branch from BLE to BGT. I’d like to change the instruction with a SM (set memory) Macsbug command, but first I have to figure out the value to set. I could guess (don’t laugh, I’ve done it before, and even got it right after just a few guesses on a couple of occasions), but a better way is to let someone do all the guessing (or table lookups) for me. The fastest tool I’ve found is TMONPro on some handy nearby machine. Here’s how:

1) Open up an assembly window. Set its address to PlayMem. That’s a chunk of memory that TMON sets aside when it loads. It’s there for you to play with.

2) Select the first line. It probably reads something like ORI.B #$00,D0. Regardless, select the whole line.

3) Now type in the instruction you want. It replaces the selection. Now press return or enter.

4) TMONPro assembles your instruction right then and there.

5) Open a memory window and point it at PlayMem. An easy way to do that is to command-click on PlayMem’s address over on the left-hand side of the assembly window. The memory window now shows the hex values for the instruction you just typed in.

Of course, you might also just use it on the machine you’re debugging. That’s even faster because now you can simply type over the line of assembly, press enter, and the code changes in place.

- Ned Flanders

Springfield

Playing a sound asynchronously and continuously

When allocating your channel, pass a callbackproc. When playing the sound using bufferCmd, immediately play a callbackCmd as well. Your callback will be called when there is about 50ms of sound left to play, and can queue a new bufferCmd in the same channel (even though it's at interrupt time).

- Jon W{tte

Sweden

[When asked about the { in his name, Jon replied :

“For reference, it's option-u a, or a-umlaut - ä. However, I'm trying to push the brace as the next character to be included in the Swedish naming character set :-)” ]

 

Community Search:
MacTech Search:

Software Updates via MacUpdate

Latest Forum Discussions

See All

How to evolve Eevee in Pokemon GO
By now, almost everyone should be hip to how to evolve Pokemon in Pokemon GO (and if not, there's a guide for that). Just gather enough candy of the appropriate type, feed them all to the Pokemon, and evolution happens. It's a miracle that would... | Read more »
CSR Racing 2: Guide to all game modes
It might not seem like there are all that many ways to go fast in a straight line, but CSR Racing 2 begs to differ. [Read more] | Read more »
Bulb Boy (Games)
Bulb Boy 1.0 Device: iOS Universal Category: Games Price: $2.99, Version: 1.0 (iTunes) Description: Multi-award winning 2D point & click horror adventure about a boy with a glowing head. | Read more »
5 top free emoji keyboard apps
If we're not at peak emoji yet as a society, it feels like we definitely should be. The emoji concept has gone far beyond what anyone in Japan could have envisioned when the people there unleashed it on an unsuspecting world, but the West has... | Read more »
How to unlock more characters in Disney...
One of the big charms of Disney Emoji Blitz is seeing a wide variety of beloved Disney and Pixar characters transformed into smiling emojis. Even someone like the sneaky Randall from Monsters Inc., who probably never cracked a smile on film, is... | Read more »
Cubway (Games)
Cubway 1.0 Device: iOS Universal Category: Games Price: $1.99, Version: 1.0 (iTunes) Description: Cubway is a journey with an abstract story of lifecycle of rebirth, called Samsara. Guide the cube through the long way full of dangers... | Read more »
Colorcube (Games)
Colorcube 1.0 Device: iOS Universal Category: Games Price: $1.99, Version: 1.0 (iTunes) Description: Turn pieces and blend colours in this minimal yet visually stunning puzzler.Over 200 handcrafted and challenging levels. Features... | Read more »
Doodle God Griddlers (Games)
Doodle God Griddlers 1.0 Device: iOS Universal Category: Games Price: $4.99, Version: 1.0 (iTunes) Description: | Read more »
Crusader Kings: Chronicles (Games)
Crusader Kings: Chronicles 1.0 Device: iOS Universal Category: Games Price: $4.99, Version: 1.0 (iTunes) Description: Crusader Kings: Chronicles is an interactive text based game that puts you in the shoes of Guy de Rose as you make... | Read more »
Roads of Rome: New Generation (Games)
Roads of Rome: New Generation 1.0 Device: iOS Universal Category: Games Price: $5.99, Version: 1.0 (iTunes) Description: | Read more »

Price Scanner via MacPrices.net

Apple price trackers, updated continuously
Scan our Apple Price Trackers for the latest information on sales, bundles, and availability on systems from Apple’s authorized internet/catalog resellers. We update the trackers continuously: - 15″... Read more
13-inch 2.5GHz MacBook Pro (Apple refurbished...
Apple has Certified Refurbished 13″ 2.5GHz MacBook Pros available for $829, or $270 off the cost of new models. Apple’s one-year warranty is standard, and shipping is free: - 13″ 2.5GHz MacBook Pros... Read more
21-inch iMacs on sale for up to $120 off MSRP
B&H Photo has 21″ iMacs on sale for up to $120 off MSRP including free shipping plus NY sales tax only: - 21″ 3.1GHz iMac 4K: $1379 $120 off MSRP - 21″ 2.8GHz iMac: $1199.99 $100 off MSRP - 21″ 1... Read more
Charitybuzz Set to Auction Unique Apple-1 Com...
Offering an opportunity to own the computer that sparked a revolution, on Monday, July 25, leading online charity auction platform Charitybuzz will auction what is claimed to be the world’s most... Read more
MacBook Airs on sale for up to $150 off MSRP
Amazon has 11″ and 13″ MacBook Airs on sale for up to $150 off MSRP for a limited time. Shipping is free: - 13″ 1.6GHz/128GB MacBook Air (sku MMGF2LL/A): $899.99 $100 off MSRP - 13″ 1.6GHz/256GB... Read more
Apple refurbished 13-inch Retina MacBook Pros...
Apple has Certified Refurbished 13″ Retina MacBook Pros available for up to $270 off the cost of new models. An Apple one-year warranty is included with each model, and shipping is free: - 13″ 2.7GHz... Read more
Apple refurbished 11-inch MacBook Airs availa...
Apple has Certified Refurbished 11″ MacBook Airs (the latest models), available for up to $170 off the cost of new models. An Apple one-year warranty is included with each MacBook, and shipping is... Read more
Apple iPad Pro Sales Far Outpacing Microsoft...
A report on Appleinsider notes that despite Microsoft Surface tablet PC sales growing by 9 percent year over year, revenues remained below $1 billion, and are down sequentially from the $1.1 billion... Read more
DEVONthink 2.9 Features Ultra-fast, Robust, A...
DEVONthink 2.9 allows users to keep databases synchronized using many means of transport. It transmits them between Macs on the local network or stores them in a syncable form on removable hard... Read more
12-inch WiFi Apple iPad Pros on sale for up t...
B&H Photo has 12″ WiFi iPad Pros on sale for up to $100 off MSRP, each including free shipping. B&H charges sales tax in NY only: - 12″ Space Gray 32GB WiFi iPad Pro: $749 $50 off MSRP - 12″... Read more

Jobs Board

*Apple* Solutions Consultant - APPLE (United...
Job Summary As an Apple Solutions Consultant, you'll be the link between our future customers and our products. You'll showcase your entrepreneurial spirit as you Read more
*Apple* Professional Learning Specialist - A...
Job Summary The Apple Professional Learning Specialist is a full-time position for one year with Apple in the Phoenix, AZ area. This position requires a high Read more
*Apple* Picker - Apple Hill Orchard (United...
Apple Hill Orchard, Co. Rte. 21,Whitehall, NY 9/7/16-10/228/16. Pick fresh market or processing apples Productivity of 60 boxes and 80 boxes processing fruit per Read more
*Apple* Solutions Consultant - APPLE (United...
Job Summary As an Apple Solutions Consultant, you'll be the link between our future customers and our products. You'll showcase your entrepreneurial spirit as you Read more
*Apple* Retail - Multiple Positions - Apple,...
Job Description:SalesSpecialist - Retail Customer Service and SalesTransform Apple Store visitors into loyal Apple customers. When customers enter the store, Read more
All contents are Copyright 1984-2011 by Xplain Corporation. All rights reserved. Theme designed by Icreon.