TweetFollow Us on Twitter

Toolbox Calls
Volume Number:1
Issue Number:3
Column Tag:Forth forum

Toolbox Calls

By Jörg Langowski

First of all let me apologize for two things. The first one is an error in my article on the floating point routines; you might already have noticed it. Page 14 of MacTech 1-1, column 2, sentence 2, last word should be ELEMS68K instead of FP68K.

Secondly, I omitted something that I promised to you, namely the words for toolbox trap calling from MacForth. Let's quickly make up for this: The word that defines an operating system call is OS.TRAP. The word defined by OS.TRAP will take the address of a parameter block from the stack and put it into register A0, then execute the trap given in the definition. OS traps returns their result in register D0, and the content of this register is saved in the predefined variable IO-RESULT before exiting. As an example you may define a call to the READ function as:

:  A002  OS.TRAP  READ  ;

Calling READ with the address of a file control block on the stack will then read the appropriate number of bytes from a file or volume.

All toolbox routines that are structured like a Pascal procedure expect their parameters on the stack in the order in which they appear in the Pascal definition in the Inside Mac manual. The Forth word MT assumes that all parameters on the stack are in their correct 32-bit format, and a toolbox call defined by MT will leave the stack unchanged before executing the trap. On execution, the parameters are cleared from the stack.

If the routine expects any 16-bit parameters (16 and 32 bits are the only possibilities), it would be a little difficult to push them on the stack correctly, since MacForth generally assumes stack items to be 32 bit long (in contrast to standard FORTH-79). Most toolbox traps, however, need at most two 16-bit items, and they are at the end of the parameter list. MacForth provides the two defining words W>MT and 2W>MT for calling traps that need one or two 16-bit parameters. These parameters can be pushed on the stack as 32-bit items and are automatically adjusted to 16 bits before the trap is executed.

Last type of toolbox calls are Pascal functions. The calling convention here is that one has to leave space on the stack for the result and then push the parameters. The function will clear the parameters from the stack upon execution and leave the result in the space provided. Four types of calls are provided through the defining words FUNC>W, FUNC>L, W>FUNC>L, L>FUNC>L,for functions (in that order) that use no parameters and return a 16-bit item, no parameters/32-bit result, 16-bit parameter/32-bit result, 32-bit parameter/32-bit result.

The line 1111 instruction

If you decompile and disassemble the code that is produced by the trap defining words, you will see that some of them contain instructions that start with a hex F. Here MacForth makes use of the other set of unimplemented instructions (line 1111 emulator) of the 68000!

Read this over again, it is important. The MacForth implementers have really made a fine use of the 68000 traps that are available. Not only are the 4E type traps used in making the threaded code fast (see my last article), here is the 1111 line trap, too. The Motorola 68000 Programmer's Reference Manual (you have it by now, haven't you) tells you where the trap vector is, it is hex 2C. At this location you find (in MacForth) the 32-bit number hex 5614. The code at $5614 looks like that shown in fig. 1.

Beautiful: A word that starts with hex F is a negative 16-bit number and can therefore be used as a negative offset into an address table that is below the base location that A4 points to. As an example, let's see how an OS trap defined through OS.TRAP is executed. Assume you defined READ like above. Then the word READ will generate the threaded code:

 FFEC [F line trap for OS.TRAP]
 A002 [READ OS call]

A4 points to $55C4 in Forth 1.1. $FFEC added to A4 gives $55B0, at which location we find the address $1850. Offset from A4, we find ourselves at $6E14. The code there is shown in figure 2.

As you see, the trap word is moved into the routine that sets up the parameter register and executes the OS call. You may try and disassemble the definitions of the Pascal function call defining words; they also work through the 1111 line trap.

'Exotic' procedure calls

Though I do not recommend to do so, you might have written your own assembly language routine that requires a 16-bit parameter on the stack somewhere in between the 32 bit parameters and therefore you cannot use one of the defining words to call it. Here is a little trick that does the job. Since MacForth does not provide a word that pushes a 16-bit value on the stack and decrements the stack pointer by only two, we define our own. The base of the stack can be accessed through the variable S0, SP@ fetches the current stack pointer and SP! stores the value of S0 in the stack pointer.

:  PUSHW  S0  @  >R  SP@  2-  S0  !
SP!  R>  S0  !  DROP  ;

is our 16-bit push. After this, of course, the stack will be screwed up for most practical Forth purposes, so be sure to use it only if you a. want to call a procedure that expects a 16-bit parameter at this position on the stack or b. if you use it twice to make a composite 32-bit item on the stack from two 16-bit items.

Windows and Controls in MacForth

The last topic that I want to deal with in this issue are some points about windowing on the Macintosh. Those of you who read David Smith's article on assembly language have probably already got a feeling how involved this can get. Even setting up a window takes quite some effort. Fortunately, the MacForth system takes most of the load off our shoulders.

The FINGER.PAINT example in the MacForth manual illustrates the ease with which basic windowing functions such as opening, closing, dragging, resizing and tracking the mouse are handled; the word DO.EVENTS takes care of many of these functions. However, the MacForth system support does not go beyond those basics. More complicated things like scrolling must be handled explicitly by you, the user. The reason for this is simply that opening, closing, dragging and sizing are functions that are handled by the Window Manager while a scroll bar is a control for which the Control Manager is responsible. Controls are supported by MacForth Level 2; Level 1 does not document controls, although some of the definitions that are used in control handling are already present in Level 1.

For example, you can add scroll bars to any window by adding the constants SCROLL.UP/DOWN or SCROLL.LEFT/RIGHT to the window attributes. Try this in the windowing example from the Level 1 manual and then click the mouse in one of the scroll bars.

Of course, the bars don't scroll anything since DO.EVENTS does not support them. In order to be able to use these and other controls, we have to go through the Control Manager. Level 1 owners, you don't have to quit here, controls are a standard concept of the Macintosh that is supported by the Mac system and may be used from anywhere, FORTH, machine language, Pascal, C, even BASIC. It is only a little simpler in Level 2 because some of the things that we have to define for ourselves are already there.

In the next issue we'll look at the Control Manager and how to use it from Forth.

FIG 1
$5614 ADDQ.L#2,SP  discard status  register
 MOVE.L (SP),A0  saved PC -> A0
 MOVE   (A0)+,D0 F-trap word ->D0
 MOVE.L A0,(SP)  updated PC ->     stack
 MOVE.L 0(A4,D0.W),D1get address of  trap routine              rel. to 
A4 -> D1
 JMP  0(A4,D1.L) jump to this routine relative                 to A4

FIG 2
$6E14 MOVE.L(SP)+,A1 put PC into A1  (points to OS             
 trap word to be executed)

 MOVE  (A1),$1858(A4)get trap word & 
 put into $1858(A4) =     $6E1C

 MOVE.L (SP)+,A0 OS parameter pointer -> A0

$6E1C AXXXTrap goes into  here. Yuck!  Self-                   modifying 
code!

 MOVE D0,A0 result code
 MOVE.L A0,38(A0,D7.L)  save in    IO-RESULT

 JMP  (A4)get next Forth  token and  ...                 execute

 

Community Search:
MacTech Search:

Software Updates via MacUpdate

BBEdit 11.1.1 - Powerful text and HTML e...
BBEdit is the leading professional HTML and text editor for the Mac. Specifically crafted in response to the needs of Web authors and software developers, this award-winning product provides a... Read more
CrossOver 14.1.3 - Run Windows apps on y...
CrossOver can get your Windows productivity applications and PC games up and running on your Mac quickly and easily. CrossOver runs the Windows software that you need on Mac at home, in the office,... Read more
Little Snitch 3.5.3 - Alerts you about o...
Little Snitch gives you control over your private outgoing data. Track background activity As soon as your computer connects to the Internet, applications often have permission to send any... Read more
OmniGraffle Pro 6.2.3 - Create diagrams,...
OmniGraffle Pro helps you draw beautiful diagrams, family trees, flow charts, org charts, layouts, and (mathematically speaking) any other directed or non-directed graphs. We've had people use... Read more
OmniFocus 2.2 - GTD task manager with iO...
OmniFocus helps you manage your tasks the way that you want, freeing you to focus your attention on the things that matter to you most. Capturing tasks and ideas is always a keyboard shortcut away in... Read more
Cocktail 8.4 - General maintenance and o...
Cocktail is a general purpose utility for OS X that lets you clean, repair and optimize your Mac. It is a powerful digital toolset that helps hundreds of thousands of Mac users around the world get... Read more
PDFKey Pro 4.3 - Edit and print password...
PDFKey Pro can unlock PDF documents protected for printing and copying when you've forgotten your password. It can now also protect your PDF files with a password to prevent unauthorized access and/... Read more
Kodi 15.0.beta1 - Powerful media center...
Kodi (was XBMC) is an award-winning free and open-source (GPL) software media player and entertainment hub that can be installed on Linux, OS X, Windows, iOS, and Android, featuring a 10-foot user... Read more
DiskCatalogMaker 6.4.12 - Catalog your d...
DiskCatalogMaker is a simple disk management tool which catalogs disks. Simple, light-weight, and fast. Finder-like intuitive look and feel. Super-fast search algorithm. Can compress catalog data... Read more
Macs Fan Control 1.3.0.0 - Monitor and c...
Macs Fan Control allows you to monitor and control almost any aspect of your computer's fans, with support for controlling fan speed, temperature sensors pane, menu-bar icon, and autostart with... Read more

Moleskine Timepage – Calendar for iCloud...
Moleskine Timepage – Calendar for iCloud, Google & Exchange 1.0 Device: iOS iPhone Category: Productivity Price: $4.99, Version: 1.0 (iTunes) Description: The most elegant calendar for your pocket and wrist, Timepage is a... | Read more »
QuizUp Gets Social in its New Update
Plain Vanilla Corp has released a new and improved version of their popular trivia game, QuizUp. The app now emphasizes social play so you can challenge friends from all over the world. [Read more] | Read more »
The Deep (Games)
The Deep 1.0 Device: iOS Universal Category: Games Price: $1.99, Version: 1.0 (iTunes) Description: Swipe Controls Delve into the deep in this retro rogue-like! Swipe to move your diver around and keep away from the enemies as you... | Read more »
Battle of Gods: Ascension (Games)
Battle of Gods: Ascension 1.0 Device: iOS Universal Category: Games Price: $2.99, Version: 1.0 (iTunes) Description: TURN-BASED TACTICAL COMBATFight tactical battles against the forces of Hades! In Battle of Gods: Ascension you play... | Read more »
Shadowmatic's Latest Update Adds a...
Shadowmatic's shadowy shadow-ness is getting a little shadowy-er thanks to a recent update that adds an Arcade Mode. [Read more] | Read more »
Sunrise Calendar and Slack Have Assimila...
Wunderlist is perhaps one of the most populat and beloved productivity apps on the App Store - and now it's gone and incorporated itself into other useful services like Sunrise Calendar and Slack. [Read more] | Read more »
Crossy Road Devs Hipster Whale are Bring...
Hipster Whale, the minds behind the rather popular (and rather great) Crossy Road, have teamed-up with Bandai Namco to create PAC-MAN 256: an absolutely bonkers looking maze runner chaser thing. | Read more »
Meet the New Spotify Music
Spotify Music  has a lot going on. They're introducing 3 new modes to serve all your musical needs, with the "Now" start page  gives you curated playlists based on your particular tastes. As you listen the app will learn more about your tastes and... | Read more »
What the Apple Watch Gets Right, and Wha...
| Read more »
Celebrate PAC-MAN's 35th Birthday W...
BANDAI NAMCO Entertainment America is celebrating PAC-MAN's 35th anniversary by releasing updates for PAC-MAN and PAC-MAN Lite for iOS. [Read more] | Read more »

Price Scanner via MacPrices.net

What Would the ideal Apple Productivity Platf...
For the past four years I’ve kept a foot in both the Mac and iPad camps respectively. my daily computing hours divided about 50/50 between the two devices with remarkable consistency. However, there’... Read more
PageMeUp 1.2.1 Ten Dollar Page Layout Applica...
Paris, France-based Softobe, an OS X software development company, has announced that their PageMeUp v. 1.2.1, is available on the Mac App Store for $9.99. The license can be installed on up to 5... Read more
Eight New Products For USB Type-C Application...
Fresco Logic, specialists in advanced connectivity technologies and ICs, has introduced two new product families targeting the Type-C connector recently introduced across a number of consumer... Read more
Scripps National Spelling Bee Launches Buzzwo...
Scripps National Spelling Bee fans can monitor the action at the 2015 Spelling Bee with the new Buzzworthy app for iOS, Android and Windows mobile devices. The free Buzzworthy app provides friendly... Read more
13-inch 2.5GHz MacBook Pro on sale for $120 o...
B&H Photo has the 13″ 2.5GHz MacBook Pro on sale for $979 including free shipping plus NY sales tax only. Their price is $120 off MSRP, and it’s the lowest price for this model (except for Apple’... Read more
27-inch 3.3GHz 5K iMac on sale for $1899, $10...
B&H Photo has the new 27″ 3.3GHz 5K iMac on sale for $1899.99 including free shipping plus NY tax only. Their price is $100 off MSRP. Read more
Save up to $50 on iPad Air 2, NY tax only, fr...
B&H Photo has iPad Air 2s on sale for up to $50 off MSRP including free shipping plus NY sales tax only: - 16GB iPad Air 2 WiFi: $469 $30 off - 64GB iPad Air 2 WiFi: $549.99 $50 off - 128GB iPad... Read more
Updated Mac Price Trackers
We’ve updated our Mac Price Trackers with the latest information on prices, bundles, and availability on systems from Apple’s authorized internet/catalog resellers: - 15″ MacBook Pros - 13″ MacBook... Read more
New 13-inch 2.9GHz Retina MacBook Pro on sale...
B&H Photo has the 13″ 2.9GHz/512GB Retina MacBook Pro on sale for $1699.99 including free shipping plus NY tax only. Their price is $100 off MSRP, and it’s the lowest price for this model from... Read more
Apple refurbished 2014 MacBook Airs available...
The Apple Store has Apple Certified Refurbished 2014 MacBook Airs available starting at $679. An Apple one-year warranty is included with each MacBook, and shipping is free: - 11″ 1.4GHz/128GB... Read more

Jobs Board

*Apple* Solutions Consultant - Retail Sales...
**Job Summary** As an Apple Solutions Consultant (ASC) you are the link between our customers and our products. Your role is to drive the Apple business in a retail Read more
*Apple* Watch SW Application Project Manager...
**Job Summary** The Apple Watch software team is looking for an Application Engineering Project Manager to work on new projects for Apple . The successful candidate Read more
Engineering Manager for *Apple* Maps on the...
…the Maps App Team get to take part in just about any new feature in Apple Maps, often contributing a majority of the feature work. In our day-to-day engineering work, we Read more
Senior Software Engineer - *Apple* SIM - Ap...
Changing the world is all in a day039s work at Apple . If you love innovation, here039s your chance to make a career of it. You039ll work hard. But the job comes with Read more
Lead *Apple* Solutions Consultant - Retail...
**Job Summary** Job Summary The Lead ASC is an Apple employee who serves as the Apple business manager and influencer in a hyper-business critical Reseller's store Read more
All contents are Copyright 1984-2011 by Xplain Corporation. All rights reserved. Theme designed by Icreon.