TweetFollow Us on Twitter

ROM Exploring
Volume Number:7
Issue Number:4
Column Tag:Pascal Procedures

Related Info: Resource Manager

Exploring the ROM

By Micheal Budiansky, Berkeley, CA

[Michael Budiansky is a physicist-turned-engineer specializing in Macintosh software. He worked in the areas of heavy-ion collisions, optical telescope design, and semiconductor image processing, before discovering the Macintosh in 1986. He’s been programming the Mac ever since, first for Bear River Associates, then for Applied Biosystems. He received a Ph.D. in Physics from the University of California at Berkeley.]

Re: Sources of Resources

Resources only come from the resource fork of disk files. Right? Wrong! Since the days of the 128K ROM a number of important resources have also been stored in the ROM itself. In this article, we’ll discuss how to get at these hidden resources - the accompanying Pascal code for a simple MPW tool illustrates the necessary technique, as well as providing a means of exploring what these resources are and finding out which of them have been modified by later patches to the System software.

The Resource Chain

First, let’s review how resources are loaded by a program. When an application requests a resource, the Resource Manager searches through a chain of resource files until it is found. Normally, the chain begins with the most-recently-opened document’s resource file, followed by the application’s resource fork, and then the System file. If the resource isn’t in the document (or if there’s no document open), the manager looks in the application. If it’s not in the application, the manager looks in the System file. If it’s not in the System file, you’re probably in trouble.

To get at the ROM resources, you’ll need to adjust the resource chain by means of techniques described in Inside Macintosh,Volumes IV and V. There are two different methods: one is to set the values of certain low-memory globals before making an ordinary Resource Manager call, and the other is to use the special toolbox call RGetResource. The first method puts the ROM resource map at the front of the resource chain for one call to the Resource Manager, as shown in Figure 1. Set the low-memory global RomMapInsert to true and then make your call; the ROM resource map will be searched first for that one call only. The second method is to use the RGetResource call; this behaves exactly like GetResource, except that it puts the ROM resource map at the end of the chain, as shown in Figure 2. After all the resource files in the chain have been searched for the requested resource, RGetResource looks in the ROM resource map.

Figure 1. Moving ROM resources to the front

Figure 2. ROM resources at front

Roving around

What are the resources in the ROM and what good are they? Obtaining the complete list is an exercise left to the reader - armed with the program that follows. (Lazy readers can look up the answer in Inside Macintosh - but those lucky enough to own one of the newer models may have to wait until volume VI is published.) Here are three examples of how these resources can be used:

First, you may find a secret resource that is not present in the system file. The only way to get at these is from the ROM. In Macintosh II class machines, for example, the ROM contains a hidden ‘snd’ resource. It’s named “Brass Horn,” (although it actually sounds more like a squeaky toy) and if it catches your fancy, you could copy it, renumber it, and paste it into your System file to use as a beep sound.

Also, you can optimize your code to use a ROM resource if it is available, thus saving the time required to read in the resource from disk. This technique is used by MacApp to save time in reading the standard cursor resources (watch, plus, cross, and I-beam). This is a fairly safe technique, since if for some reason the resource that you expected to be in ROM is not there, the Resource manager will simply continue looking for it farther along the resource file chain (probably to find it in the System file). You need to be a little careful, however, since sometimes resources are present in both the System file and in the ROM for a reason: the one in ROM is no good any more, and the System file version is a replacement!

Finally, you may need to know about the ROM resources if you want to replace or modify one of the standard system resources. If a resource is first loaded into the System Heap from the ROM, then it doesn’t matter if you edit the copy in the System file--you’re stuck with the ROM version. As it does for so many other functions, however, the Macintosh operating system provides a “hook” that lets you override the default behavior: the ‘Rov#’ resource. The System file contains a number of ‘Rov#’ resources; a ‘Rov#’ resource contains a list of types and ID numbers of ROM resources that are to be replaced by their System file counterparts. In current systems, there is one ‘Rov#’ resource for each version of the ROM (e.g., Mac Plus in resource #117, Mac SE in resource #630, Mac II in resource #376, etc.). By editing the appropriate ‘Rov#’ resource in the System file, you can instruct the system to ignore the ROM version of a resource and to use the version in the System file itself. Readers who are now all set to disassemble and rewrite the Disk Driver ROM resource may proceed without further delay; they probably wouldn’t pay much attention to the safety lecture below, anyway. As for the rest of you, there is an example of resource overriding that may be of interest to any programmer, even those who aren’t the daredevil type.

The Monaco font is a clean, monospaced, font--ideal for viewing program listings on the screen. Its one deficiency, however, is that the digit ‘0’ and the capital letter ‘O’ are indistinguishable, as are the lower case ‘l’ and the capital letter ‘I’. You can repair this problem by using ResEdit to edit the Monaco ‘FONT’ resources (9 point and 12 point) in a copy of your System file: add a dot in the middle of the zero digit and add serifs (short horizontal lines at the top and bottom of the character) to the capital ‘I’. (Please! edit a copy, not your current and/or only version of the System file! And read the safety lecture, too!) If you try out this edited System file on a Mac newer than the Plus, however, you will probably find that while the modifications appear when you use Monaco 12, they do NOT when you use Monaco 9; that’s because Monaco 9 is in a ROM resource. To use the System file’s version of the font, you must edit the ‘Rov#’ resource appropriate for your machine by adding a entry for ‘FONT’ number 521. This will take a certain amount of skill with ResEdit, since to add the entry requires editing the resource in hex form. Open the ‘Rov#’ as a general hex resource. The second word (group of 4 hex digits) in the resource is the number of overridden resources minus one. Edit this number to be one greater than its current value, then add three words of zeroes at the end of the resource; these three words are placeholders for the new entry. Close the resource, then open it again, in the ordinary way that uses the ‘Rov#’ template. The last entry in the list should be blank; change it to FONT 521. If you run into trouble, refer to Inside Macintosh IV-20 for the detailed format of the ‘Rov#’ resource. (Note: Inside Macintosh, Volume IV says that you’ll need to obtain a ‘Rovr’ resource from Developer Tech Support at Apple before you can do any overriding; current System files already contain this resource, so there’s no need to bug the folks at DTS to send it to you.)

ROMRes tool: Theory & Practice

This MPW tool has three options for exploring the ROM resources, plus a self-contained help text. If no option or an invalid option is supplied, the help text is printed out; this is a convenient feature for MPW tools in general, particularly those that are not likely to be used frequently. The listing feature (-l) looks up and lists all resources in the ROM; resources are listed by type, ID, and name. The override feature (-r) looks in your System file and lists all the ‘Rov#’ resources found. For each one, it lists the ROM resources that are flagged to be overridden. Note that only the resources listed for the particular ‘Rov#’ that matches your machine will actually be overridden in your machine. The extract feature (-x) copies a particular resource from the ROM into the file of your choice; if the file does not exist, it will be created.

The comment at the beginning of the code contains the text for the make file; copy the text between (* and *) and paste it into a file named ‘ROMRes.make’. The main section of the program sets up a few variables and then has a case statement that dispatches control to one of three subroutines, one for each feature. If there is a problem with the command line arguments, the code at the end of the main section prints out the help text. The tool gets access to the text on the command line via the global variables ArgC and ArgV, which are defined in the unit IntEnv included in the MPW development system.

The tool uses the first method described above for gaining access to the ROM resources: setting the appropriate low-memory global to TRUE. The routine that lists all the ROM resources deserves some comment. This routine examines all the resources in the resource chain, and identifies those that are in the ROM by using the call HomeResFile; HomeResFile returns a reference number of 1 for resources in ROM. The value 1 is ordinarily an illegal value for a resource file reference number, but in this one case it is used to identify the source of ROM resources. The call CurResFile does not return a value of 1, even if you have set the low-memory global RomMapInsert to true. Trying the call UseResFile(1) will not give good results either. The ROM resource map is not a “file,” and it does not work in general to pretend that it is. This explains why we can’t simply use the Resource Manager calls Count1Types, Count1Resources, and Get1IndResource to examine resources that are only in the ROM. These calls, described in volume IV of Inside Macintosh, search the current resource file only, rather than the entire resource chain, but they don’t behave the way you might expect for the ROM resource map.

Safety lecture

First of all, if you choose to use ResEdit on your System file, be aware that it’s serious business. Back up your files, work on a copy of your System file, and be prepared for your system to crash if you make a mistake. MacTutor readers are a pretty fearless bunch, but even rock climbers use ropes, so you should take reasonable precautions when experimenting with your System.

Almost as fearsome as system crashes are lawyers. If you filch some nifty resource out of the ROM, it’s fine to play around with it on your own machine, but before you include it in an insanely great application to be distributed for fame and fortune, it might be a good idea to talk to Software Licensing at Apple.

Software compatibility is what separates the professionals from the amateurs. Obviously, if you write a program that depends on a ROM resource being there, you are asking for trouble when a new model of the Macintosh comes out. Similarly, if you write a program that expects a newer ROM version, you may unnecessarily be shutting out thousands of Mac owners with a Plus or SE. More subtle (i.e., hard to debug) problems may arise if your program demands a ROM version of a resource when the current System file actually supplies a new and improved version of the resource. Remember, your users will not thank you for saving them a few microseconds by reading a resource from ROM instead of disk if it costs them hours of trying to figure out why the program doesn’t work with a new System version!

Happy exploring!

PROGRAM ROMRes;
(* ROMRes.Make

ROMRes.p.o ƒ ROMRes.Make 
 ROMRes.p
 Pascal ROMRes.p  

ROMRes ƒƒ   ROMRes.Make 
 ROMRes.p.o
 Link -w -t ‘MPST’ -c ‘MPS ‘ 
 ROMRes.p.o 
 “{Libraries}”Runtime.o 
 “{Libraries}”Interface.o 
 “{PLibraries}”PasLib.o 
 “{Libraries}”ToolLibs.o 
 -o ROMRes
*)

USES
 MemTypes,
 QuickDraw,
 OSIntf,
 ToolIntf,
 PackIntf,
 SysEqu,
 Signal,
 PasLibIntf,
 IntEnv;

TYPE
 IntPtr = ^INTEGER;

VAR
 printUsage:BOOLEAN;
 flagPtr: IntPtr;
 numTypes:INTEGER;
 theType: ResType;
 aType: ResType;
 numOfType: INTEGER;
 index: INTEGER;
 aHandle: Handle;
 theID: INTEGER;
 name:  Str255;

 {=========================}
 PROCEDURE ListROMResources;

 VAR
 i:INTEGER;
 k:INTEGER;

 BEGIN
 flagPtr^ := mapTrue;
 numTypes := CountTypes;
 { Scan all types of resources }
 FOR i := 1 TO numTypes DO
 BEGIN
 flagPtr^ := mapTrue;
 GetIndType(theType, i);
 flagPtr^ := mapTrue;
 numOfType := CountResources(theType);
 { Scan all resources of each type }
 FOR k := 1 TO numOfType DO
 BEGIN
 flagPtr^ := mapFalse;
 aHandle := GetIndResource(theType, k);
 GetResInfo(aHandle, theID, aType, name);
 flagPtr^ := mapFalse;
 { Only print the ROM resources }
 IF HomeResFile(aHandle) = 1 THEN
  Writeln(theType,’ ‘, theID,’ ‘,name);
 END;
 END;
 END;

 {=========================}
 PROCEDURE ListROvResources;

 TYPE
 OneROv = PACKED RECORD
 rType: ResType;
 rID: INTEGER;
 END;
 ROvType = PACKED RECORD
 romVersion:INTEGER;
 count: INTEGER;
 rovs:  PACKED ARRAY [0..32000] OF OneROv;
 END;
 ROvTypePtr = ^ROvType;
 ROvTypeHdl = ^ROvTypePtr;

 VAR
 i:INTEGER;
 k:INTEGER;
 rovHandle: ROvTypeHdl;

 BEGIN
 numOfType := CountResources(‘ROv#’);
 FOR k := 1 TO numOfType DO
 BEGIN
 aHandle := GetIndResource(‘ROv#’, k);
 GetResInfo(aHandle, theID, aType, name);
 rovHandle := ROvTypeHdl(aHandle);
 Writeln(‘ROv# ‘, theID:0);
 Write(‘  Rom version ‘, rovHandle^^.romVersion:0,’ - ‘);
 { Identify ROM version type }
 CASE rovHandle^^.romVersion OF
 117: Writeln(‘Mac Plus’);
 376: Writeln(‘Mac II’);  
 630: Writeln(‘Mac SE’);  
 890: Writeln(‘Mac Portable’);
 1660:  Writeln(‘Mac IIci’);
 OTHERWISE
 Writeln(‘ Unknown’);
 END;
 { List contents of each Rov# }
 FOR i := 0 TO rovHandle^^.count DO
 BEGIN
 Writeln(‘  ‘, rovHandle^^.rovs[i].rType, ‘ ‘,
 rovHandle^^.rovs[i].rID:0);
 END;
 Writeln;
 END;
 END;
 
 {===========================}
 PROCEDURE ExtractROMResource;
 VAR
 rType: ResType;
 rTypePtr:StringPtr;
 value: LongInt;
 rID:   INTEGER;
 fileName:Str255;
 i:INTEGER;
 refNum:INTEGER;
 BEGIN
 { Get desired type from command line }
 rType := ‘    ‘;
 rTypePtr := StringPtr(@rType);
 FOR i := 1 TO Ord(argV^[2]^[0]) DO
 rTypePtr^[i - 1] := argV^[2]^[i];
 { Get ID number from command line }
 StringToNum(argV^[3]^, value);
 rID := INTEGER(value);
 { Get output file name from command line }
 fileName := argV^[4]^;
 { Get ROM resource, if there }
 flagPtr^ := mapTrue;
 aHandle := GetResource(rType, rID);
 IF aHandle = NIL THEN
 Writeln(‘No such resource’)
 ELSE
 BEGIN
 Writeln(‘Extracting ‘,rType, ‘ ‘, rID:0, ‘ to file ‘,fileName);
 GetResInfo(aHandle, theID, aType, name);
 HNoPurge(aHandle);
 DetachResource(aHandle);
 { Open output file; create it if it doesn’t exist }
 refNum := OpenResFile(fileName);
 IF refNum = -1 THEN
 BEGIN
 IF Create(fileName, 0, ‘RSED’,    ‘rsrc’) = noErr THEN
 BEGIN
 CreateResFile(fileName);
 refNum := OpenResFile(fileName);
 END;
 END;
 IF refNum = -1 THEN
 Writeln(‘Problem with file’)
 ELSE
 BEGIN
 AddResource(aHandle, rType, rID, name);
 CloseResFile(refNum);
 END;
 END;
 END;

BEGIN
 { if error in command line, print info }
 printUsage := TRUE;
 { save pointer to low-mem global, for convenience }
 flagPtr := IntPtr(RomMapInsert);
 { act on option: -l -r or -x }
 IF argC > 1 THEN
 IF (Ord(argV^[1]^[0]) > 1) AND 
 (argV^[1]^[1] = ‘-’) THEN
 CASE argV^[1]^[2] OF
 ‘l’:
 BEGIN
 ListROMResources;
 printUsage := FALSE;
 END;
 ‘r’:
 BEGIN
 ListRovResources;
 printUsage := FALSE;
 END;
 ‘x’:
 IF argC > 4 THEN
 BEGIN
 ExtractROMResource;
 printUsage := FALSE;
 END;
 END;
 { print instructions if problem with command line }
 IF printUsage THEN
 BEGIN
 Writeln(‘ROMRes [option ]’);
 Write(‘    -l                            #’);
 Writeln(‘ list types and ids of ROM resources’);
 Write(‘    -r                            #’);
 Writeln(‘ list all overridden resources’);
 Write(‘    -x resType resID outputFile   #’);
 Writeln(‘ extract a ROM resource and write to file’);
 END;
END.

 
AAPL
$98.63
Apple Inc.
-0.39
MSFT
$43.92
Microsoft Corpora
-0.05
GOOG
$585.19
Google Inc.
-5.41

MacTech Search:
Community Search:

Software Updates via MacUpdate

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
TotalFinder 1.6.2 - Adds tabs, hotkeys,...
TotalFinder is a universally acclaimed navigational companion for your Mac. Enhance your Mac's Finder with features so smart and convenient, you won't believe you ever lived without them. Tab-based... Read more
Vienna 3.0.0 RC 2 :be5265e: - RSS and At...
Vienna is a freeware and Open-Source RSS/Atom newsreader with article storage and management via a SQLite database, written in Objective-C and Cocoa, for the OS X operating system. It provides... Read more
VLC Media Player 2.1.5 - Popular multime...
VLC Media Player is a highly portable multimedia player for various audio and video formats (MPEG-1, MPEG-2, MPEG-4, DivX, MP3, OGG, ...) as well as DVDs, VCDs, and various streaming protocols. It... Read more
Default Folder X 4.6.7 - Enhances Open a...
Default Folder X attaches a toolbar to the right side of the Open and Save dialogs in any OS X-native application. The toolbar gives you fast access to various folders and commands. You just click... Read more
TinkerTool 5.3 - Expanded preference set...
TinkerTool is an application that gives you access to additional preference settings Apple has built into Mac OS X. This allows to activate hidden features in the operating system and in some of the... Read more
Audio Hijack Pro 2.11.0 - Record and enh...
Audio Hijack Pro drastically changes the way you use audio on your computer, giving you the freedom to listen to audio when you want and how you want. Record and enhance any audio with Audio Hijack... Read more
Intermission 1.1.1 - Pause and rewind li...
Intermission allows you to pause and rewind live audio from any application on your Mac. Intermission will buffer up to 3 hours of audio, allowing users to skip through any assortment of audio... Read more

Latest Forum Discussions

See All

Note Review
Note Review By Jennifer Allen on July 29th, 2014 Our Rating: :: TOO SIMPLEiPhone App - Designed for the iPhone, compatible with the iPad Note is a note taking app that’s a little too short on features to be worth its asking price... | Read more »
Chainsaw Warrior Goes on Sale & Ther...
Chainsaw Warrior Goes on Sale & There’s a Chance to Win a Copy of the Original Board Game Posted by Jennifer Allen on July 29th, 2014 [ permalink | Read more »
It Came From Canada: Tiny Tower Vegas
If you go to a casino, you might make a lot of money. If you run a casino, you’re guaranteed to make a lot of money. The choice seems pretty obvious. So while waiting for your shady real estate deals to move forward, get prepared with Tiny Tower... | Read more »
Z Hunter Review
Z Hunter Review By Lee Hamlet on July 29th, 2014 Our Rating: :: RIGHT ON TARGETUniversal App - Designed for iPhone and iPad While it might not necessarily break new ground, Z Hunter has enough tricks up its sleeve to ensure that... | Read more »
Huge Update Comes To Duet, Adding 48 New...
Huge Update Comes To Duet, Adding 48 New Stages Posted by Jennifer Allen on July 29th, 2014 [ permalink ] Universal App - Designed for iPhone and iPad | Read more »
Sharknado: The Video Game Available Now....
Sharknado: The Video Game Available Now. Seriously. Posted by Rob Rich on July 29th, 2014 [ permalink ] Universal App - Designed for iPhone and iPad | Read more »
Frog Orbs 2 Review
Frog Orbs 2 Review By Nadia Oxford on July 29th, 2014 Our Rating: :: THIS MAGIC IS A TAD MONOTONOUS Universal App - Designed for iPhone and iPad Frog Orbs 2 is repetitive, but younger players should enjoy it nonetheless.   | Read more »
Puzzix Review
Puzzix Review By Jennifer Allen on July 29th, 2014 Our Rating: :: NICE IDEAUniversal App - Designed for iPhone and iPad A little like Tetris, Puzzix is all about piecing together blocks and watching them vanish. It could do with... | Read more »
Cannonball eMail is Now Live – Works Wit...
Cannonball eMail is Now Live – Works With Gmail, Yahoo, Outlook, Hotmail, and AOL Posted by Jessica Fisher on July 29th, 2014 [ permalink ] | Read more »
To The End Review
To The End Review By Lee Hamlet on July 29th, 2014 Our Rating: :: A VICIOUS CYCLEUniversal App - Designed for iPhone and iPad To The End will test players’ patience, timing, and dedication as they try to navigate all 13 levels in... | Read more »

Price Scanner via MacPrices.net

Updated MacBook Pro Price Trackers
We’ve updated our MacBook Pro Price Trackers with the latest information on prices, bundles, and availability on the new 2014 models from Apple’s authorized internet/catalog resellers as well as... Read more
Apple updates MacBook Pros with slightly fast...
Apple updated 13″ and 15″ Retina MacBook Pros today with slightly faster Haswell processors. 13″ models now ship with 8GB of RAM standard, while 15″ MacBook Pros ship with 16GB across the board. Most... Read more
Apple drops price on 13″ 2.5GHz MacBook Pro b...
The Apple Store has dropped their price for the 13″ 2.5GHz MacBook Pro by $100 to $1099 including free shipping. Read more
Apple drops prices on refurbished 2013 MacBoo...
The Apple Store has dropped prices on Apple Certified Refurbished 13″ and 15″ 2013 MacBook Pros, with model now available starting at $929. Apple’s one-year warranty is standard, and shipping is free... Read more
iOS 8 and OS X 10.10 To Support DuckDuckGo As...
Writing for Quartz, Dan Frommer reports that Apple’s forthcoming iOS 8 and OS X 10.10 operating systems version updates will allow users to select DuckDuckGo as their default search engine. He notes... Read more
U.K. Hospital Using iPods and iPads To Record...
British news journal GazetteLive’s. Ian McNeal notes that the old “an apple a day keeps the doctor away” proverb is being turned on its head at http://southtees.nhs.uk/hospitals/james-cook/ James... Read more
13-inch 2.5GHz MacBook Pro on sale for $1099,...
Best Buy has the 13″ 2.5GHz MacBook Pro available for $1099.99 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
Roundup of Apple refurbished MacBook Pros, th...
The Apple Store has Apple Certified Refurbished 13″ and 15″ MacBook Pros available for up to $400 off the cost of new models. Apple’s one-year warranty is standard, and shipping is free. Their prices... Read more
Record Mac Shipments In Q2/14 Confound Analys...
A Seeking Alpha Trefis commentary notes that Apple’s fiscal Q3 2014 results released July 22, beat market predictions on earnings, although revenues were slightly lower than anticipated. Apple’s Mac’... Read more
Intel To Launch Core M Silicon For Use In Not...
Digitimes’ Monica Chen and Joseph Tsai, report that Intel will launch 14nm-based Core M series processors specifically for use in fanless notebook/tablet 2-in-1 models in Q4 2014, with many models to... Read more

Jobs Board

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
*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
*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
All contents are Copyright 1984-2011 by Xplain Corporation. All rights reserved. Theme designed by Icreon.