TweetFollow Us on Twitter

TMON Debugging
Volume Number:1
Issue Number:10
Column Tag:Assembly Language Lab

Debugging Techniques and TMON Review"

By Paul Snively, Columbus, IN., MacTutor Contributing Editor

I was just reading my Volume 1, No. 4 MacTutor and came across William Gladnick's letter asking about tips, utilities, and debugging techniques. OK, I'll bite!

MacsBug Snoops the ROMS

As far as useful utilities go, first, get a 512K system. Then get MacNOSY and TMON (the latter is from TMQ software). These, plus a good assembler (MacASM, in other words) are all that you really need to do serious Mac hacking.

As for tips, here's one: the Mac ROMs are buggy, and nearly everyone knows it. What's not so obvious is how to use MacsBug to trace through the ROMs step by step (rather than treating the A-traps as a single instruction). Wouldn't it be nice to be able to trace one instruction at a time while in a ROM routine? OK, here's how: write your application (I assume that you are using one assembler or another). The first instruction should be:

 LABEL   BRA   LABEL

followed by your program. Assemble the program in the usual way. Install MacsBug in your system. Double-click your program's icon. The system will seem to hang, since you told it to BRanch Always to LABEL, which is where the branch is. In other words, your program is in an infinite loop. Press the interrupt button on your Mac. MacsBug will be entered with the PC pointing to your BRA instruction. Bump the PC by two to point past the BRA. Now start tracing your program.

How to Trace the ROM Routines

As you are tracing or stepping through your code with MacsBug, the disassembly will eventually say something along the lines of "OSTRAP A219" or "TOOLBOX A912" or what have you. STOP! DO NOT TRACE OR STEP! Now, change the value in A7 downward by six bytes. In other words, if A7 is now 00123AC7, change it to 00123AC1. This is to simulate the stack setup caused by the 68000 during exception processing.

Now, look at the current PC value. Let's say it's 00004E56. Store this address at A7+2 using the SM command, like this:

SM 00123AC3 00 00 4E 56 

Now type PC 401018. You may now continue tracing or what have you. Essentially, you have done manually what the 68000 would have done automatically upon encountering the A-trap. 401018 is the address of the Macintosh A-trap dispatch routine. Observe the code as you trace through it; it's quite interesting. For example, the main difference between OSTRAPs and TOOLBOX traps is that for OSTRAPs, which require an I/O buffer address in A0 and return a status code in D0, A0 and D0 must not be saved on the stack across the actual code. Apple accomplished this by setting bit 11 in all of the TOOLBOX instructions (in other words, the second hexadecimal digit of a TOOLBOX trap will always be at least 8). The dispatch code at 401018 examines that bit to determine whether or not to save A0 and D0 (and possibly some other registers) on the stack.

More important, you can watch as the dispatch code determines via a lookup table where to go in the ROMs, and you can trace through those high-power ROM routines that we've all come to know and love. Now you can see for yourself exactly how a window is opened, or what have you.

The ability to trace through the ROMs, coupled with MacNOSY's capability of outputting labels, as opposed to addresses, makes for a relatively simple way of learning how the Mac works right down at the nuts and bolts level - which is right up MacTutor's alley, right, guys?

May all of your hacking - er, excuse me, I mean programming - be bug free!

TMON Thoughts

Some of you may have seen TMQ Software's ad in MacTutor lately. They're pushing a product called TMON, which at first made me laugh - TMON was the name of the first machine language monitor I ever actually laid my mits upon; it was for my (at the time) tape based Model I TRS-80. You can see why I laughed.

Nevertheless, TMQ promised some interesting things, like tracing ROM and setting up to seven breakpoints. Also, they claimed that TMON was a multiple-window monitor/debugger. Just the idea that a debugger could be multiple window boggled me. The thing must be huge. Especially if it can disassemble, do hex dumps, heap displays, register displays, and so on simultaneously.

The price looked pretty reasonable for all of this: the ad asked for $100.00, which is less than I paid for MacASM, my assembler of choice. I finally broke down and ordered TMON from TMQ. It arrived a few days after I ordered it; if you're willing to pay for it, TMQ will ship UPS blue label, which is how I prefer to work.

After using TMON and configuring it and reconfiguring it and debugging some of my own code and tinkering around with some code that I didn't write, I can make the following observations.

Love at First Byte

First, if you don't already own a copy of TMON, run, don't walk, to get your checkbook and order it now. If you are a serious developer (and if you are reading this, chances are pretty good that you are) you should be using TMON. Use TMON once and you'll never boot MacsBug again. I promise.

The ads really don't do it justice. They don't tell you about the interactive assembler/disassembler; they don't tell you about the fact that dump and disassembly windows can be "anchored" to registers and are continually updated; they don't tell you that TMON allows access to any online resource file; they don't tell you about the customizable user area; they don't tell you about the sophisticated label support, or the screen buffering, or the rich implementation of interrupt button functions... The list goes on.

Think of TMON as MacsBug and MacNosy combined, with some things thrown in that neither MacsBug nor MacNosy was intended to do. To be fair about it, since MacNosy is a disassembler and not a debugger, there are some features that MacNosy has that TMON doesn't. I recommend both of them if you are serious about Mac programming.

TMON's fast window system will impress you, as will its implementation of menus. It takes a little getting used to; both windows and the menubar are handled a little differently from "normal" Mac windows and menus.

Mouse Unfreeze

The menus are Dump, Asmbly, Brkpnts, Regs, Heap, File, Exit, GoSub, Step, Trace, Options, Num, User, and Print. Another feature that TMON implements via a command keystroke is called Mouse Unfreeze. Yes, you read right - if your program crashes and your mouse freezes up but the keyboard is still listening, you can unfreeze the mouse. Wild stuff.

Dump opens a window which is initially a dump starting at address 000000. There is a blinking cursor on the first line. As long as the cursor is on the first line, the address can be changed. You can type in any expression, label, or register to anchor to (as well as a special virtual register called V). The window will be instantaneously updated to show the new dump. More importantly, if you anchor to a register (say A0), whenever the contents of A0 changes the window will be updated to reflect the change. You won't believe how useful this is until you see it.

Disassembler Anchored to the PC Counter

'Asmbly' is the interactive assembler / disassembler. When you open this window, you get a disassembly starting at 000000, which doesn't make much sense, since there is no valid code there. You'll probably want to anchor the disassembly window to the PC. Like the dump window, when you anchor the disassembly window to a register it gets updated every time the register changes. Anchoring the disassembly window to the PC causes the window to be updated every time you step, trace, gosub, or exit to the program (actually, since exit actually transfers control to the program, the window will not be updated unless control returns to the monitor).

TMON normally displays A-traps as labels, not numbers, although this can be changed in order to conserve space. TMON also supports user-defined label tables. The TMON master disk includes a file called System.MAP which is a label file of all of the low memory equates on the Macintosh. This MAP file can be loaded into TMON so that features of TMON that support labels (nearly all of them, in other words) can now refer to low RAM areas (with labels like CurApName and so on) by name instead of address. This aspect of TMON, unfortunately, requires 512K.

TMON includes sophisticated customization support that allows you to fine tune TMON to your needs. TMON is quite capable of running on a 128K machine, and contrary to what you might think, it does not have to be hopelessly crippled in order to do so. I can use A-trap names and, with a compressed screen buffer of 4K, do some meaningful debugging. A 512K Mac sure would help, though.

TMON has an alternate register save area. This is interesting. You can come close to a routine that you think will crash, save the registers, execute the routine, and if it crashes (an exception lands you back in TMON), you can reload the registers and try again, and so forth. Kind of like being in suspended animation.

We all know that the interrupt button on the Mac is good for something. TMON knows it, too. Pressing the button from an application will get you into TMON, just like it does with MacsBug. However, there are several special-purpose keystroke-interrupt combinations that TMON has over MacsBug.

Pressing interrupt while holding down the command key restarts the monitor. This is considered a drastic step to be taken only when all else fails. This often has the effect of mulching part of TMON. The nice thing is that TMON is constantly checking itself, and if it thinks it's been damaged, it will say so.

Cmd-Option-Interrupt!

If that doesn't work, try command - option - interrupt. This does a really total monitor reset, which makes it definitely last-resort material.

Now for the interesting one. The user area supplied with TMON contains a function called Trap Signal. The manual calls the Trap Signal function a "smart interrupt," which is a pretty apt description. Trap Signal allows you to specify a trap or range of traps to apply this function to, as well as an optional address or address range. Once you've done that, go ahead and execute your program.

Nothing happened, right? You're program should be whizzing merrily along. Now press interrupt while holding down the option key. This activates the trap signal, which won't go into effect until your trap and address range criteria are met. That's why it's called a smart interrupt: it doesn't stop until it hits the right trap/PC location. This allows you to interrupt your program at a specific place rather than going into it blind. A good trap to put a smart interrupt on would be _GetNextEvent, since it tends to be at the main loop of any Mac application.

Trace uses the Trace bit

TMON's trace, step, and GoSub features are very nice and very powerful. TMQ Software saw fit to do what no one else did: they use the trace bit of the status register to force a trace interrupt, which the monitor traps. This is the essence of tracing under TMON. The trace function even allows you to watch as the A-trap dispatcher finds the address of the A-trap's code and executes it. This means that my little note concerning tracing the ROMs under MacsBug doesn't apply here; TMON's trace does it automatically. Step in TMON is exactly like trace except that A-traps are treated as a single instruction. GoSub is like step except that subroutines (executed by JSR or BSR) are executed in full without tracing.

The heap windows are something else. Not only do they show what blocks exist and whether the block is locked, purgable, relocatable, and what have you; they also show what is in the block (to the best of TMON's ability). You can see at a glance which block contains CODE segment number one of your program, which block contains the font that is currently in use, which blocks contain resources pertinent to the application, and so on. You can also examine the system heap in the same manner. A heap window can be made to switch from appplication heap to system or vice-versa by hitting the TAB key (which puts the cursor at the top of the window) and hitting the RETURN or ENTER key.

The file window is extremely useful. It shows the contents of all currently open resource files. For those resources that are in memory, their handle is given. For those that haven't been loaded from disk yet, "Nowhere" is displayed. Resources of any type and ID can be loaded using the standard user area LoadRes utility.

If a window is too limited to show you as much as you would like of what it is you're looking at, you can probably print it with the user area print utility. You can specify dump printing, disassembly printing, file printing, or heap printing. For dumps and disassemblies you must specify an address range. For files TMON needs the resource file number, and for heap prints it needs 0 for the system heap and a non-zero value for the application heap.

There are lots of other handy features, too, such as block moves, block compares, block fills, checksumming of memory, label table support, a very efficient heap scramble, a find utility, the ability to show the application's screen, and the ability to completely reset the system.

User Extensible via MDS

To make matters even better, the author includes the source code to the entire default user area on the TMON disk. The point is that sophisticated Mac programmers can write their own user area utilities that can either replace or augment the ones included with TMON. The source is in MDS format, and a link file is included to link the resulting object code into TMON. Obviously, you must have MDS for this to be of any use. Frankly, I think it'll be a long time before anyone comes up with a way to improve upon TMON's already fantastic user area routines.

That about wraps it up. My idea of an ideal Mac debugging setup is a 512K Mac running TMON. Use the normal default user area, then add in the System.MAP file. This will allow TMON to refer to low memory areas by name (which is handy if you're doing ROM disassemblies in particular). Now you can really debug! Goodbye, MacsBug; hello, TMON!

 

Community Search:
MacTech Search:

Software Updates via MacUpdate

Capture One 15.3.1 - RAW workflow softwa...
Capture One is a professional RAW converter offering you ultimate image quality with accurate colors and incredible detail from more than 400 high-end cameras - straight out of the box. It offers... Read more
Connect Fonts 23.0.3 - Font management s...
Connect Fonts is the creative professional's font manager. Every professional font manager should deliver the basics: spectacular previews, powerful search tools, and efficient font organization. You... Read more
CleanMyMac X 4.11.0 - Delete files that...
CleanMyMac X makes space for the things you love. Sporting a range of ingenious new features, CleanMyMac lets you safely and intelligently scan and clean your entire system, delete large, unused... Read more
Firefox 102.0 - Fast, safe Web browser.
Firefox offers a fast, safe Web browsing experience. Browse quickly, securely, and effortlessly. With its industry-leading features, Firefox is the choice of Web development professionals and casual... Read more
Hopper Disassembler 5.6.1 - Binary disas...
Hopper Disassembler is a binary disassembler, decompiler, and debugger for 32- and 64-bit executables. It will let you disassemble any binary you want, and provide you all the information about its... Read more
Skim 1.6.11 - PDF reader and note-taker...
Skim is a PDF reader and note-taker for OS X. It is designed to help you read and annotate scientific papers in PDF, but is also great for viewing any PDF file. Skim includes many features and has a... Read more
Alfred 4.6.7 - Quick launcher for apps a...
Alfred is an award-winning productivity application for OS X. Alfred saves you time when you search for files online or on your Mac. Be more productive with hotkeys, keywords, and file actions at... Read more
Transmit 5.8.7 - Excellent FTP/SFTP clie...
Transmit is an excellent FTP (file transfer protocol), SFTP, S3 (Amazon.com file hosting) and iDisk/WebDAV client that allows you to upload, download, and delete files over the internet. With the... Read more
Adobe Lightroom Classic 11.4.1 - Import,...
You can download Lightroom for Mac as a part of Creative Cloud for only $9.99/month with Photoshop, included as part of the photography package. The latest version of Lightroom gives you all of the... Read more
MarsEdit 4.5.9 - Quick and convenient bl...
MarsEdit is a blog editor for OS X that makes editing your blog like writing email, with spell-checking, drafts, multiple windows, and even AppleScript support. It works with with most blog services... Read more

Latest Forum Discussions

See All

Apple Arcade Weekly Round-Up: Major Upda...
Apple recently revealed July’s upcoming Apple Arcade releases in a new App Store Story, and this week’s new release is My Bowling 3D+ featuring offline and online multiplayer support, and more. It arrives from the developers of Pro Darts 2022+ and... | Read more »
Downhill Mountain Biking Game ‘Descender...
Just over three years ago in May of 2019 developer RageSquid and publisher No More Robots released a quirky downhill mountain biking game called Descenders on PC and Xbox One. Bemoaning a lack of “extreme sports" titles in recent years led RageSquid... | Read more »
SwitchArcade Round-Up: ‘Monster Hunter R...
Hello gentle readers, and welcome to the SwitchArcade Round-Up for June 30th, 2022. Thursday is once more upon us, and that means a bunch of new releases to look at. We start things off with DLC for some very big games, Monster Hunter Rise and... | Read more »
‘HOOK 2’ Review – A Sharp Left Hook From...
The original HOOK ($1.99) had a very simple idea behind it. You were presented with a tangled mess of hooks and loops, and you needed to remove each one without snagging any others. Extremely simple at first, but as the puzzles rolled along,... | Read more »
‘Dicey Dungeons’ Mobile Version Launchin...
After a very long wait, Terry Cavanagh’s dungeon crawling roguelite deckbuiler hybrid experience Dicey Dungeons is coming to mobile platforms next week alongside a huge free DLC pack on all platforms. This DLC will be included in the mobile... | Read more »
Distract Yourself With These Great Mobil...
Every day, we pick out a curated list of the best mobile discounts on the App Store and post them here. This list won't be comprehensive, but it every game on it is recommended. Feel free to check out the coverage we did on them in the links below... | Read more »
‘Danganronpa S: Ultimate Summer Camp’ is...
If you’ve been following Danganronp over the last few years, Spike Chunsoft celebrated its anniversary by bringing the series to mobile in the form of anniversary editions. After the first two released, there was a long delay for V3, but it finally... | Read more »
Out Now: ‘HOOK 2’, ‘Incoherence’, ‘Juras...
Each and every day new mobile games are hitting the App Store, and so each week we put together a big old list of all the best new releases of the past seven days. Back in the day the App Store would showcase the same games for a week, and then... | Read more »
Upcoming Mobile MMO RPG Shooter ‘Avatar:...
This past January a contingent of developers made up of Archosaur Games, Tencent, Lightstorm Entertainment, and Disney announced a new mobile game set in James Cameron’s Avatar universe titled Avatar: Reckoning. | Read more »
Culinary Platformer ‘Chefy-Chef’ Coming...
If your name is Chefy, it’s pretty much a given that you should be a chef. Such is the case with Chefy-Chef, a game from Bug Studio about a chef named Chefy who must travel to all sorts of exotic locations using a magical refrigerator in an effort... | Read more »

Price Scanner via MacPrices.net

July 4th sale at Verizon: Apple AirPods Pro f...
Verizon has Apple AirPods Pro on sale for $179.99 on their online store as part of their Fourth of July sale. Their price is $70 (28%) off Apple’s MSRP, and it’s among the lowest prices currently... Read more
Apple is now selling Certified Refurbished Ma...
Apple has added a full line of standard-configuration Mac Studios available in their Certified Refurbished section starting at only $1799 and ranging up to $400 off MSRP. Each Mac Studio comes with... Read more
Open-box 14″ M1 Pro MacBook Pros in stock tod...
QuickShip Electronics has open-box return Space Gray 14″ M1 Pro MacBook Pros in stock and on sale for $300-$450 off MSRP on their eBay store today. According to QuickShip, “The item in this listing... Read more
Can Being An iPhone User Really Determine Whe...
FEATURE: – If you’re traveling on the road today for the July 4th holiday, you might want to keep your Apple smartphone locked up inside the car’s glove compartment for your (and, everyone else’s)... Read more
2nd generation 4K Apple TVs with Siri remote...
Apple has restocked a full line of Certified Refurbished 2nd generation 32GB and 64GB 4K Apple TVs with Siri remotes for $30 off the cost of new models. Apple’s standard one-year warranty is included... Read more
Back in stock: Apple Watch Series 7 models fo...
Apple has restocked Certified Refurbished Apple Watch Series 7 WiFi-only models in their online store for $60-$70 off MSRP, starting at $339. Each Watch includes Apple’s standard one-year warranty, a... Read more
July 4th Sale at Expercom: $200 off any 16″ M...
Apple reseller Expercom has 16″ M1 Pro and M1 Max MacBook Pros available for $200 off MSRP as part of their July 4th sale. In addition to their MacBook Pro sale prices, take $50 off AppleCare+ when... Read more
10.2″ Apple iPads (WiFi models) are on sale f...
Amazon has Apple’s 9th generation 10.2″ WiFi iPads on sale for up to $20-$50 off MSRP for a limited time. Their prices are the lowest price currently available for one of these iPads. All models are... Read more
10-Core M1 Pro 14″ MacBook Pros on sale for $...
B&H Photo is offering $200 discounts on Apple’s new 14″ M1 Pro MacBook Pros with 10-Core CPUs (16GB RAM/1TB SSDs). Free 1-2 day shipping is available to most US addresses, and both models are in... Read more
B&H has 16-inch M1 Pro MacBook Pros in st...
New Space Gray 16″ MacBook Pros with Apple’s M1 Pro CPUs are in stock and on sale today at B&H Photo for $200 off Apple’s MSRP. Sale prices are for M1 Pro models with 512GB or 1TB of SSD storage... Read more

Jobs Board

VP, Software Engineering - *Apple* and Andr...
…Client Application Software Engineering team is seeking a VP, Software Engineering for Apple and Android. You will lead the client engineering team building Disney+, Read more
I/S Senior Engineer - *Apple* Systems Engin...
**19647BR** **Position Title:** I/S Senior Engineer - Apple Systems Engineering - Remote **Department:** Information Systems **Location:** Lakeland, FL between Read more
*Apple* IT Support Analyst - 2nd Shift - Zon...
Apple IT Support Analyst - 2nd Shift Professional Services Albany, New York Malta, New York Clifton Park, New York Menands, New York Syracuse, New York Watertown, Read more
Infotainment Certification Test Engineer (XC)...
…integration - CarPlay, android auto, MirrorLink, Baidu Carlife, MFi/iPod certification testing; Apple PPID preparation, Google HUCD and GTM preparation + 3 years of Read more
Workplace Services *Apple* Device Managemen...
…3350 Riverwood Parkway Suite 900, Atlanta, GA, 30339 USA **Workplace Services Apple Device Management** **Role Overview** Carrier is seeking an experienced and Read more
All contents are Copyright 1984-2011 by Xplain Corporation. All rights reserved. Theme designed by Icreon.