TweetFollow Us on Twitter

Winter 92 - APPLE II Q & A

APPLE II Q & A

APPLE II Developer Technical Support

Q What's the best way to do text-only printing to a character device through GS/OS? 

A If you want to print text to a GS/OS character device, here's how you do it:

  1. Look at all the on-line devices to find which are character devices. You can tell when a device is a character device by examining bit 7 of the "characteristics" word returned by DInfo--the bit is set for block devices and clear for character devices. You don't have to hard-code a list of character device IDs.
  2. Present the user with a list of device names followed by their location and generic type in parentheses. You can adjust the names of device types to reflect your use. For example, ".RPM (AppleTalk printer, port 1)," ".DEV2 (serial modem, port 2)," or ".DEV3 (generic character device, slot 5)." You can use bit 3 of the slot returned by DInfo to know whether to return "slot" or "port," too.
  3. When the user selects a printing device, call Open on the device name (such as .RPM for an AppleTalk printer). Use Write to write the information, just as you would to a file; then call Close (you can call Flush if you like, but it shouldn't be necessary). That's all you need to do.

Remember not to embed ImageWriter or any other printer-specific codes in the output stream. With the exception of choosing a device and creating a file, this same code could be used to print to any  text printer or to another device such as a disk or modem. You might give users a "text printing preferences" dialog where they can enter some codes if they like, and you might have built-in sets for ImageWriters and other common printers, but don't make it too complicated. These instructions are very generic and will work well on any setup, not just an ImageWriter II connected through the serial port.

Q On a ROM 03 Apple II GS, I save and restore the mouse mode by getting it from ReadMouse, setting the mode to what I need, and restoring the value (with SetMouse) when done. This sometimes kills the mouse--I don't get any mouse movement until my program quits. Help! By the way, this isn't a problem on ROM 01 machines.  

A The ROM 03 mouse firmware doesn't behave as documented in two respects. First, it sometimes returns an illegal mouse mode value from ReadMouse. Specifically, there's garbage in the high nibble of the mouse mode byte. Second, SetMouse returns an error and takes no action when passed an invalid mode, even though the Apple IIGS Toolbox Reference  says it returns no errors. When you try to restore the invalid mode, nothing happens and the mouse stays in whatever mode you had it in--if it's not what the system needs, the mouse will appear "hung" until someone sets the mode to what the system does need.

You can work around this problem by masking off the high nibble of the mode result from ReadMouse (AND #$000F in 65816 assembly) before passing it to SetMouse. This problem is fixed in Apple IIGS system software version 6.0-- ReadMouse always returns a valid mode under 6.0.

Q When I call SFMultiGet2, I randomly get error $1705 (bad pathname descriptor in the reply record) even though that error doesn't mean anything for that call. Any ideas? 

A All versions of SFMultiGet2 before Apple II GS System 6.0 incorrectly look at two of the words in the reply record (offsets $0008 and $000E) to make sure they don't contain the value $0002. That value would be illegal in those positions--in any of the other  new Standard File calls. SFMultiGet2 doesn't use the same reply record, but pre-6.0 versions of Standard File accidentally check those fields anyway. Make sure the values in bytes that are past the beginning of the 6-byte reply record are not $0002. This is fixed in System 6.0.

Q Although my application fully supports GS/OS, the Finder uses slashes instead of colons in the pathnames in message #1. This means my application can't open any files that have slashes in the filename. 

A The Finder and its message-passing conventions were originally released before GS/OS was written. Applications depend on the slash (/) as the separator character to be able to parse these pathnames (for example, to find the filename to use in a document window title). If the separator character were to change, many older applications would break.

Finder version 6.0 may support an additional message containing a list of fully expanded GS/OS pathnames. These pathnames use colons as separators and aren't limited to 255 characters. See the Finder 6.0 documentation for details on using this message.

Q I've written a program that hangs inside Standard File under Apple II GS System 5.0.4, but works fine under development versions of 6.0. I'm not using any 6.0-specific features. What could be the problem? 

A Standard File before System 6.0 does not behave gracefully if called with both prefix 0 and prefix 8 empty. Try setting one of these prefixes to an existing directory and see if your problem vanishes.

Q I can't find the ProDOS partition on Volume IX or later of the Developer CD Series discs. What's happened? 

A Apple II information was duplicated on all Developer CDs from Volume III through Volume VIII because without the ProDOS partition, Apple II users couldn't see the information, and without the Apple II folder on the HFS partition, the information couldn't be shared on an AppleShare file server (or Macintosh System 7 File Sharing). Apple II GS System 6.0 includes an HFS (Macintosh) file system translator, which means that Apple II GS developers can access the information on the HFS partition, making the ProDOS partition unnecessary.

The Apple II information can be found on the HFS partition with the pathname Dev.CD Vol. IX:Development Platforms (Moof!):Apple II. Note that this means the Apple II folder can only be accessed from ProDOS 8 using AppleShare with long naming on--the path to the Apple II folder is not a legal ProDOS 8 pathname.

Q Apple II Applesoft's floating-point routine results are sometimes accurate to only two places. For example, the answer returned for PRINT 55555.099-55555.09 is 9.01031494 E-03. How can we get more accurate results? 

A The accuracy loss you're experiencing with the Applesoft floating-point routines is normal. If you convert a number such as 55555.099 to a base 2 floating-point number, you won't get an exact representation using Applesoft's floating-point routines or even 96-bit precision IEEE numerics. Because 9.01031494 E-03 is 0.0090103, you can see that you have accuracy out to three and a half decimal places. The solution is to determine the accuracy that you want and massage the result to give you that accuracy. Here's a sample program that shows common Applesoft rounding techniques:

1 REM Round to 3 decimal places of accuracy example
10 Input a
20 Input b
30 If a-b>1000 then 100: REM no 3-digit rounding of numbers >1000
40 Print "Standard Applesoft Non-accurate result:";a-b
50 Print "Truncated result:";
   INT((a-b)*1000)/1000 60 Print "Rounded result:";
   INT(((a-b)+.0001)*1000)/1000
70 Goto 10
100 Print "Result has 3 decimal accuracy already:";a-b
110 Goto 10

This is the only way that you can get Applesoft to clip the numbers, apart from using a separate floating-point engine. Alternatively, you can do your own conversion from Applesoft internal numeric format to a string in assembly language and have it simulate the above operation when converting the number.


Kudos to our readers who care enough to ask us terrific and well thought-out questions. The answers are supplied by our teams of technical gurus; our thanks to all. Special thanks to Matt Deatherage, Jim Luther, Dave Lyons, Jim Mensch, and Tim Swihart for the material in this Q & A column. *



Have more questions? Need more answers? Take a look at the Dev Tech Answers library on AppleLink (updated weekly) or at the Q & A stack on the Developer CD Series  disc.*

 

Community Search:
MacTech Search:

Software Updates via MacUpdate

How to become the ultimate robot warrior...
Chrono Strike is a delightfully immersive beat ‘em up with a sense of humor (any game with a good Sims reference gets points in my book). [Read more] | Read more »
Tips and tricks to get a higher score in...
Snow Roll is a devilish endless runner very much in the vein of Flappy Bird. It revels in its dastardly level of difficulty, and doesn’t really care how angry you get at it as it knows you’ll keep coming back for more. [Read more] | Read more »
How to win big in Slots Deluxe
Cheating while gambling is illegal and morally wrong, and in some parts of the world it leads to men with names like Vinnie "Six Knuckles" Manchenzo beating you to a pulp in a dark alley. [Read more] | Read more »
How to take over the world in Dictator 2
Running a country isn't easy - especially when you're a dictator who wants to take over the world and crush everyone in your path while you do it. [Read more] | Read more »
Tips and tricks to get a higher score in...
Tank.iois - you guessed it! - another multiplayer arena battler likeAgar.io and Slither.io. It does differentiate itself by putting you in a tiny tank though, so it's not exactly the same. To help you get that all-important high score, we've got a... | Read more »
How to unlock characters in One Tap Tenn...
As the title suggests, One Tap Tennis requires only a single tap to play its particular brand of tennis, and rewards you with a ton of unlockable characters if you perform well. Fortunately for you, we at 148Apps have got a few tips and tricks to... | Read more »
Grab it now: Game Craft’s Legend of War...
The real time strategy game is now available for you to sink your teeth into, through the App Store and Google Play. Combining elements of skill, strategy and empire building, Legend of War is a real gamers’ game. [Read more] | Read more »
Skateboard Party 3 ft. Greg Lutzka (Gam...
Skateboard Party 3 ft. Greg Lutzka 1.0 Device: iOS Universal Category: Games Price: $1.99, Version: 1.0 (iTunes) Description: Skateboard Party is back! This third edition of the popular sports franchise features professional skater... | Read more »
Cubious (Games)
Cubious 1.0 Device: iOS Universal Category: Games Price: $.99, Version: 1.0 (iTunes) Description: Cubious – How smart are you? How high is your IQube? Solve the impossible puzzles to find out, and help a lost little cube find his... | Read more »
Goat Simulator Waste of Space (Games)
Goat Simulator Waste of Space 1.1 Device: iOS Universal Category: Games Price: $4.99, Version: 1.1 (iTunes) Description: ** IMPORTANT - SUPPORTED DEVICESiPhone 4S, iPad 2, iPod Touch 5 or better.** | Read more »

Price Scanner via MacPrices.net

Enterprise Workers Pick Technology Over Perks...
New Adobe study shows surprising attitudes about office jobs and where the future of work is heading. Adobe has released survey findings revealing that a surprising 70 percent of U.S. office workers... Read more
Memorial Day Weekend Sale: $50-$100 off 11-in...
B&H Photo has 13″ and 11″ MacBook Airs with 256GB SSDs on sale for $50-$100 off MSRP. Shipping is free, and B&H charges NY sales tax only: - 11″ 1.6GHz/256GB MacBook Air: $999 $100 off MSRP... Read more
Memorial Day Weekend Sales: Apple MacBook Pro...
B&H Photo has 13″ and 15″ Retina MacBook Pros on sale for up to $210 off MSRP. Shipping is free, and B&H charges NY tax only: - 15″ 2.2GHz Retina MacBook Pro: $1799 $200 off MSRP - 15″ 2.5GHz... Read more
Memorial Day Weekend Sales: Apple iMacs and M...
Take up to $150 off the price of a new iMac or Mac mini at the following Apple resellers this Memorial Day weekend: iMacs: B&H Photo has 21″ and 27″ iMacs on sale for up to $150 off MSRP... Read more
Apple refurbished Retina MacBook Pros availab...
Apple has Certified Refurbished 2015 13″ and 15″ Retina MacBook Pros available for up to $380 off the cost of new models. An Apple one-year warranty is included with each model, and shipping is free... Read more
Apple refurbished 11-inch MacBook Airs availa...
Apple has Certified Refurbished 11″ MacBook Airs (the latest models), available for up to $170 off the cost of new models. An Apple one-year warranty is included with each MacBook, and shipping is... Read more
Goal Zero and OtterBox Partner to Expand iPh...
Goal Zero, specialists in portable power, have announced a partnership with OtterBox, brand smartphone case protection, to offer the Slide and Slide Plus Batteries as modules compatible with the new... Read more
15-inch Retina MacBook Pros on sale for up to...
B&H Photo has 15″ Retina MacBook Pros on sale for up to $210 off MSRP. Shipping is free, and B&H charges NY tax only: - 15″ 2.2GHz Retina MacBook Pro: $1799 $200 off MSRP - 15″ 2.5GHz Retina... Read more
Clearance 2015 13-inch MacBook Airs available...
B&H Photo has clearance 2015 13″ MacBook Airs available for $250 off original MSRP. Shipping is free, and B&H charges NY sales tax only: - 13″ 1.6GHz/4GB/128GB MacBook Air (MJVE2LL/A): $799... Read more
Apple refurbished Apple TVs available for up...
Apple has Certified Refurbished 32GB and 64GB Apple TVs available for up to $30 off the cost of new models. Apple’s standard one-year warranty is included with each model, and shipping is free: -... Read more

Jobs Board

*Apple* Solutions Consultant - APPLE (United...
Job Summary As an Apple Solutions Consultant, you'll be the link between our future customers and our products. You'll showcase your entrepreneurial spirit as you Read more
*Apple* Project Engineer - Smart Source Inc...
SmartSource is in need of an Apple Project Engineer for a 12 month contract opportunity in Pittsburg, PA. Role: Apple Project Engineer Location: Pittsburg, PA Read more
Automotive Sales Consultant - Apple Ford Linc...
…you. The best candidates are smart, technologically savvy and are customer focused. Apple Ford Lincoln Apple Valley is different, because: $30,000 annual salary Read more
Service Assistant - *Apple* Chevrolet *App...
Apple Automotive is one of the fastest growing dealer...and it shows. Consider making the switch to the Apple Automotive Group today! At Apple Automotive, we Read more
Editor, *Apple* News - APPLE (United States...
Job Summary The Apple News team is looking for a passionate and knowledgeable editor with experience covering entertainment/pop culture and experience running social Read more
All contents are Copyright 1984-2011 by Xplain Corporation. All rights reserved. Theme designed by Icreon.