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.

 

Community Search:
MacTech Search:

Software Updates via MacUpdate

FileZilla 3.24.0 - Fast and reliable FTP...
FileZilla (ported from Windows) is a fast and reliable FTP client and server with lots of useful features and an intuitive interface. Version 3.24.0: New The context menu for remote file search... Read more
Bookends 12.7.8 - Reference management a...
Bookends is a full-featured bibliography/reference and information-management system for students and professionals. Bookends uses the cloud to sync reference libraries on all the Macs you use.... Read more
Duplicate Annihilator 5.8.3 - Find and d...
Duplicate Annihilator takes on the time-consuming task of comparing the images in your iPhoto library using effective algorithms to make sure that no duplicate escapes. Duplicate Annihilator detects... Read more
BusyContacts 1.1.6 - Fast, efficient con...
BusyContacts is a contact manager for OS X that makes creating, finding, and managing contacts faster and more efficient. It brings to contact management the same power, flexibility, and sharing... Read more
MarsEdit 3.7.10 - Quick and convenient b...
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
BusyCal 3.1.4 - Powerful calendar app wi...
BusyCal is an award-winning desktop calendar that combines personal productivity features for individuals with powerful calendar sharing capabilities for families and workgroups. Its unique features... Read more
VirtualBox 5.1.14 - x86 virtualization s...
VirtualBox is a family of powerful x86 virtualization products for enterprise as well as home use. Not only is VirtualBox an extremely feature rich, high performance product for enterprise customers... Read more
Bookends 12.7.8 - Reference management a...
Bookends is a full-featured bibliography/reference and information-management system for students and professionals. Bookends uses the cloud to sync reference libraries on all the Macs you use.... Read more
VirtualBox 5.1.14 - x86 virtualization s...
VirtualBox is a family of powerful x86 virtualization products for enterprise as well as home use. Not only is VirtualBox an extremely feature rich, high performance product for enterprise customers... Read more
FileZilla 3.24.0 - Fast and reliable FTP...
FileZilla (ported from Windows) is a fast and reliable FTP client and server with lots of useful features and an intuitive interface. Version 3.24.0: New The context menu for remote file search... Read more

Super Mario Run dashes onto Android in M...
Super Mario Run was one of the biggest mobile launches in 2016 before it was met with a lukewarm response by many. While the game itself plays a treat, it's pretty hard to swallow the steep price for the full game. With that said, Android users... | Read more »
WarFriends Beginner's Guide: How to...
Chillingo's new game, WarFriends, is finally available world wide, and so far it's a refreshing change from common mobile game trends. The game's a mix of tower defense, third person shooter, and collectible card game. There's a lot to unpack here... | Read more »
Super Gridland (Entertainment)
Super Gridland 1.0 Device: iOS Universal Category: Entertainment Price: $1.99, Version: 1.0 (iTunes) Description: Match. Build. Survive. "exquisitely tuned" - Rock Paper Shotgun No in-app purches, and no ads! | Read more »
Red's Kingdom (Games)
Red's Kingdom 1.0 Device: iOS Universal Category: Games Price: $4.99, Version: 1.0 (iTunes) Description: Mad King Mac has kidnapped your father and stolen your golden nut! Solve puzzles and battle goons as you explore and battle your... | Read more »
Turbo League Guide: How to tame the cont...
| Read more »
Fire Emblem: Heroes coming to Google Pla...
Nintendo gave us our first look at Fire Emblem: Heroes, the upcoming mobile Fire Emblem game the company hinted at last year. Revealed at the Fire Emblem Direct event held today, the game will condense the series' tactical RPG combat into bite-... | Read more »
ReSlice (Music)
ReSlice 1.0 Device: iOS Universal Category: Music Price: $9.99, Version: 1.0 (iTunes) Description: Audio Slice Machine Slice your audio samples with ReSlice and create flexible musical atoms which can be triggered by MIDI notes or... | Read more »
Stickman Surfer rides in with the tide t...
Stickson is back and this time he's taken up yet another extreme sport - surfing. Stickman Surfer is out this Thursday on both iOS and Android, so if you've been following the other Stickman adventures, you might be interested in picking this one... | Read more »
Z-Exemplar (Games)
Z-Exemplar 1.4 Device: iOS Universal Category: Games Price: $3.99, Version: 1.4 (iTunes) Description: | Read more »
5 dastardly difficult roguelikes like th...
Edmund McMillen's popular roguelike creation The Binding of Isaac: Rebirth has finally crawled onto mobile devices. It's a grotesque dual-stick shooter that tosses you into an endless, procedurally generated basement as you, the pitiable Isaac,... | Read more »

Price Scanner via MacPrices.net

Twelve South Releases RelaxedLeather Cases fo...
Inspired by the laid-back luxury of burnished leather boots and crafted in rich tones of taupe, herb and marsala, RelaxedLeather cases deliver smart, easy protection for the iPhone 7. Each genuine... Read more
Week’s Best Deal: New 2016 13-inch 2.0GHz Mac...
Amazon has the new 2016 13″ 2.0GHz non-Touch Bar MacBook Pros on sale for a limited time for $225 off MSRP including free shipping: - 13″ 2.0GHz MacBook Pro, Space Gray (MLL42LL/A): $1274.99 $225 off... Read more
Back in stock: Apple refurbished Mac minis fr...
Apple has Certified Refurbished Mac minis available starting at $419. Apple’s one-year warranty is included with each mini, and shipping is free: - 1.4GHz Mac mini: $419 $80 off MSRP - 2.6GHz Mac... Read more
Apple Ranked ‘Most Intimate Brand’
The top ranked ‘”intimate” brands continued to outperform the S&P and Fortune 500 indices in revenue and profit over the past 10 years, according to MBLM’s Brand Intimacy 2017 Report, the largest... Read more
B-Eng introduces SSD Health Check for Mac OS
Fehraltorf, Switzerland based independant Swiss company- B-Eng has announced the release and immediate availability of SSD Health Check 1.0, the company’s new hard drive utility for Mac OS X. As the... Read more
Apple’s Education discount saves up to $300 o...
Purchase a new Mac or iPad using Apple’s Education Store 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
4-core 3.7GHz Mac Pro on sale for $2290, save...
Guitar Center has the 3.7GHz 4-core Mac Pro (MD253LL/A) on sale for $2289.97 including free shipping or free local store pickup (if available). Their price is a $710 savings over standard MSRP for... Read more
128GB Apple iPad Air 2, refurbished, availabl...
Apple has Certified Refurbished 128GB iPad Air 2s WiFis available for $419 including free shipping. That’s an $80 savings over standard MSRP for this model. A standard Apple one-year warranty is... Read more
13-inch 2.7GHz Retina MacBook Pro on sale for...
B&H Photo has the 2015 13″ 2.7GHz/128GB Retina Apple MacBook Pro on sale for $100 off MSRP. Shipping is free, and B&H charges NY tax only: - 13″ 2.7GHz/128GB Retina MacBook Pro (MF839LL/A): $... Read more
Laptop Market – Flight To Quality? – The ‘Boo...
Preliminary quarterly PC shipments data released by Gartner Inc. last week reveal an interesting disparity between sales performance of major name PC vendors as opposed to that of less well-known... Read more

Jobs Board

*Apple* MAC Infrastructure Engineer - InnoCo...
Summary: Responsible for all aspects of Apple Desktop hardware. This includes research, design, test, and deploy technologies being researched by the desktop Read more
*Apple* & PC Desktop Support Technician...
Apple & PC Desktop Support Technician job in Manhattan, NY Introduction: We have immediate job openings for several Desktop Support Technicians with one of our most Read more
Senior Workstation Administrator - *Apple*...
…with extraordinary HR. QualificationsJOB SUMMARY/OVERVIEWThe Senior Workstation Administrator - Apple supports the mission of TriNet by providing advanced level Read more
Intermediate *Apple* macOS Systems Integrat...
**Position Summary:** SC3 is actively seeking an Intermediate Apple macOS systems integration administrator that will be responsible for providing Apple Mac Read more
*Apple* & PC Desktop Support Technician...
Apple & PC Desktop Support Technician job in Los Angeles, CA Introduction: We have immediate job openings for several Desktop Support Technicians with one of our Read more
All contents are Copyright 1984-2011 by Xplain Corporation. All rights reserved. Theme designed by Icreon.