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

Luminar 1.0.2 - Powerful, adaptive, conf...
Luminar is the new full-featured image editor that adapts to the way you edit photos. Over 300 essential tools to fix, edit, and enhance your photos with comfort. The future of photo editing is here... Read more
WhatRoute 2.0.10 - Geographically trace...
WhatRoute is designed to find the names of all the routers an IP packet passes through on its way from your Mac to a destination host. It also measures the round-trip time from your Mac to the router... Read more
Slack 2.3.3 - Collaborative communicatio...
Slack is a collaborative communication app that simplifies real-time messaging, archiving, and search for modern working teams. Version 2.3.3: Fixed window zoom jumping back-and-forth OS X 10.9... Read more
Lens Blur 1.4.3 - True out-of-focus boke...
Lens Blur transforms your existing photo into true SLR-quality out-of-focus bokeh effect! Everyone needs a gorgeous personalized background for a social profile, blog, Web/UI design, presentation, or... Read more
CleanMyMac 3.6.0 - $39.95
CleanMyMac 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 files... Read more
DEVONthink Pro 2.9.8 - Knowledge base, i...
DEVONthink Pro is your essential assistant for today's world, where almost everything is digital. From shopping receipts to important research papers, your life often fills your hard drive in the... Read more
MacFamilyTree 8.1 - Create and explore y...
MacFamilyTree gives genealogy a facelift: modern, interactive, convenient and fast. Explore your family tree and your family history in a way generations of chroniclers before you would have loved.... Read more
HoudahSpot 4.2.7 - Advanced file-search...
HoudahSpot is a powerful file search tool. Use HoudahSpot to locate hard-to-find files and keep frequently used files within reach. HoudahSpot will immediately feel familiar. It works just the way... Read more
TunnelBear 3.0.7 - Subscription-based pr...
TunnelBear is a subscription-based virtual private network (VPN) service and companion app, enabling you to browse the internet privately and securely. Features Browse privately - Secure your data... Read more
Garmin Express 4.5.0.0 - Manage your Gar...
Garmin Express is your essential tool for managing your Garmin devices. Update maps, golf courses and device software. You can even register your device. Update maps Update software Register your... Read more

Latest Forum Discussions

See All

Amateur Surgeon 4 Guide: Become the worl...
It's time to wield your trusty pizza cutter again, as Amateur Surgeon has returned with a whole fresh set of challenges (and some old, familiar ones, too). Starting anew isn't easy, especially when all you have at your disposal is a lighter, the... | Read more »
Le Parker: Sous Chef Extraordinaire (Ga...
Le Parker: Sous Chef Extraordinaire 1.0 Device: iOS Universal Category: Games Price: $2.99, Version: 1.0 (iTunes) Description: | Read more »
Telltale Games really is working on a Gu...
Telltale Games' next episodic adventure is indeed Guardians of the Galaxy. A document tied to the voice actors strike suggested that the project was in the work, but now we have direct confirmation following an announcement at the Game Awards that... | Read more »
Amateur Surgeon returns to iOS and Andro...
Amateur Surgeon and its two sequels disappeared from the App Store some time and it was sad days for all. But now, just in time for the holidays, the Adult Swim favorite makes its joyous return in the shape of Amateur Surgeon 4, a remake with... | Read more »
The best board games on mobile
Sometimes you need to ditch all of the high speed, high action games in favor of something a little more traditional. If you don't feel like parting ways from your mobile device, though, there are still plenty of ways to get that old-school fix.... | Read more »
The best Facebook Messenger Instant Game...
Facebook's new Instant Games is now here, meaning you can play games with your friends directly via Facebook. It's a fun new way to connect with friends, of course, but it's also proving to be a solid gaming experience in its own right, with a... | Read more »
You can now play game's on Facebook...
Facebook launched its new Instant Games platform in an exciting new attempt to engage its user base. As a result, you can now play a number of different games directly through Facebook Messenger. All of these games run with HTML5, meaning you play... | Read more »
Apollo Justice Ace Attorney (Games)
Apollo Justice Ace Attorney 1.00.00 Device: iOS Universal Category: Games Price: $.99, Version: 1.00.00 (iTunes) Description: Court Is Back In Session Star as rookie defense attorney, Apollo Justice, as he visits crime scenes,... | Read more »
KORG iWAVESTATION (Music)
KORG iWAVESTATION 1.0 Device: iOS Universal Category: Music Price: $19.99, Version: 1.0 (iTunes) Description: A revolutionary new world of sound.The Wave Sequence Synthesizer for iPad - KORG iWAVESTATION | Read more »
Don't Grind Guide: Tips for becomin...
Don’t Grind is a surprising, derpy little one touch game with fun hand-drawn graphics. The goal is simple -- get the high score without being chopped to bits. That can be tough when you’re not used to the game, and that’s compounded by the fact... | Read more »

Price Scanner via MacPrices.net

Parallels Toolbox 1.3 for Mac Offers 25 Singl...
Parallels has launched Parallels Toolbox 1.3 for Mac, an upgrade that adds five new utilities to the stand-alone application which was released in August and is available exclusively online at http... Read more
OWC Mercury Elite Pro Dual mini Ultra-Portabl...
OWC has introduced the new OWC Mercury Elite Pro Dual mini, a powerful yet ultra-portable dual-drive RAID solution. The new Mercury Elite Pro Dual mini packs phenomenal performance into a small... Read more
Clearance 13-inch Retina MacBook Pros availab...
B&H Photo has clearance 2015 13″ Retina Apple MacBook Pros available for up to $200 off original MSRP. Shipping is free, and B&H charges NY tax only: - 13″ 2.7GHz/128GB Retina MacBook Pro: $... Read more
Roundup of 2016 13-inch 2.0GHz MacBook Pro sa...
B&H has the non-Touch Bar 13″ MacBook Pros in stock today for $50-$100 off MSRP. Shipping is free, and B&H charges NY sales tax only: - 13″ 2.0GHz MacBook Pro Space Gray (MLL42LL/A): $1449 $... Read more
New 13-inch 2.0GHz Space Gray MacBook Pro in...
Adorama has the new 13″ 2.0GHz Space Gray MacBook Pro (non-Touch Bar, MLL42LL/A) in stock for $1499 including a free 3-year AppleCare Protection Plan. Shipping is free, and Adorama charges sales tax... Read more
Finnair Adopts iOS Enterprise iPad Apps from...
Finnair and IBM have announced a first-of-its-kind agreement to utilize iOS enterprise apps from IBM to support the airline’s overall digital transformation. Finnair is focused on Asia-Europe traffic... Read more
Tech21 Launches Evo Go iPhone 7 Case Availabl...
Tech21 has announced the launch of the Evo Go case for Apple iPhone 7 and iPhone 7 Plus, exclusively at T-Mobile. Available online and at participating T-Mobile stores nationwide, Evo Go cases start... Read more
Apple Turns (RED) with More Ways to Join the...
In recognition of World AIDS Day, Apple is offering more ways than ever for customers to join (RED) in its mission to create an AIDS-free generation. Apple is the worlds largest corporate contributor... Read more
Deals on new 15-inch Touch Bar MacBook Pros,...
B&H Photo has new 2016 Apple 15″ Touch Bar MacBook Pro models in stock today with some available for $50 off MSRP, each including free shipping plus NY sales tax only: - 15″ 2.7GHz Touch Bar... Read more
12-inch Retina MacBooks on sale for up to $10...
12-inch Retina MacBooks remain on sale at B&H Photo with models available for up to $100 off MSRP. Shipping is free, and B&H charges NY sales tax only. B&H will also include a free copy... Read more

Jobs Board

*Apple* Retail - Multiple Positions- White P...
Sales Specialist - Retail Customer Service and Sales Transform Apple Store visitors into loyal Apple customers. When customers enter the store, you're also the Read more
Automotive Detailer - *Apple* Used Autos -...
We are currently conductinginterviews and will be accepting applications for a part-time detailer. Apple Used Autos is a great place to work andstart a career. We Read more
*Apple* Retail - Multiple Positions - Apple,...
Job Description: Sales Specialist - Retail Customer Service and Sales Transform Apple Store visitors into loyal Apple customers. When customers enter the store, Read more
US- *Apple* Store Leader Program - Apple (Un...
…Summary Learn and grow as you explore the art of leadership at the Apple Store. You'll master our retail business inside and out through training, hands-on Read more
*Apple* & PC Desktop Support Technician...
Apple & PC Desktop Support Technician job in Dallas TX Introduction: We have immediate job openings for several Desktop Support Technicians with one of our most Read more
All contents are Copyright 1984-2011 by Xplain Corporation. All rights reserved. Theme designed by Icreon.