TweetFollow Us on Twitter

Mar 97 Tips

Volume Number: 13 (1997)
Issue Number: 3
Column Tag: Tips & Tidbits

Tips & Tidbits

By Steve Sisak

Whenever you directly or indirectly modify code, you need to make sure the processor caches are synchronized in order to avoid confusing the processor and/or emulator. This includes not only self-modifying code, but also creating routine descriptors and loading code resources by hand.

If you move 68k code with BlockMove on any system (68k or PowerPC) the caches are flushed automatically (assuming blocks greater than 12 bytes). Use BlockMoveData for blocks containing no code, since they do not require the cache flushing overhead.

Note that on a PowerPC, BlockMove does not flush PPC caches at all. The only reason BlockMove flushes 68k code is for backward compatibility with software written before the '040s. It is unfortunate that a frequently-used routine like BlockMove should have to know anything about instruction caches. On the bright side, most developers do not need to copy PPC code around, since fragment preparation occurs within CFM.

On a PPC machine, calls to the 68k cache flushing routines (including FlushCodeCacheRange and indirectly via BlockMove) do everything necessary to maintain 68k instruction cache coherency. On the original 68k emulator, this meant nothing needed to be done since there was no cached code. On the DR Emulator and Speed Emulator, these calls force the emulator to "throw out" any recompiled code associated with the specified code range.

I know the different cache flushing routines are confusing and not very well documented. Here are some simple rules:

If you are dealing with 68k instructions, use BlockMove or FlushCodeCacheRange. They both specify a range of memory and therefore do not require the newer recompiling 68k emulators to perform a complete cache flush (a very time-intensive operation that can degrade performance significantly.)

If you are dealing with PPC code, you probably don't need to worry about the issue because your code was probably directly or indirectly prepared by CFM. However, if you do generate PPC code on the fly, you should call MakeDataExecutable on the range. Note that this does more than just flushing the cache. It does everything (including flushing the processor's prefetch queue) necessary to deal with newly-generated code.

Hope this helps clear things up. If you want more details, check out the tech note I wrote while I was still at Apple on the DR Emulator.

Eric Traut
Connectix Corp.

(Almost) Painless Mixing of C and Pascal Strings

It's fair to say that most of us have found ourselves in this situation: "The API wants C-style strings and all I have are these Pascsal strings!". The typical solution is to use utilities like PtoCStr and CtoPStr to shuffle the bytes around. Consider the following example where sprintf is being used to create a menu title.

void DescribeFile (Str255 title, Str255 fileName, Str255 volumeName, 
unsigned long size)
{
    // Temporarily convert fileName and volumeName to C strings
 PtoCStr (fileName);
 PtoCStr (volumeName);
    // Use sprintf to describe the file eg. "File foo on bar (120.5K)"
 sprintf ((char*) title, "File %s on %s (%.2fK)",
 (char*) fileName,
 (char*) volumeName,
 (double) size / 1024.0);
    // Convert title, fileName and volumeName to Pascal strings
    // back to Pascal strings
 CtoPStr ((char*) title);
 CtoPStr ((char*) fileName);
 CtoPStr ((char*) volumeName);
}

As you know there's at least one unused byte at the end of the Pascal string, and the string is not a literal, you can take a shortcut by making the Pascal strings "hybrid strings". A "hybrid string" is a null-terminated pascal string. Observe:

void DescribeFile (Str255 title, Str255 fileName, Str255 volumeName,unsigned 
long size)
{
    // Convert fileName and volumeName to hybrid strings
 fileName [fileName [0] + 1] = ‘\0';
 volumeName [volumeName [0] + 1] = ‘\0';
    // Use sprintf to describe the file eg. "File foo on bar (120.5K)"
    // Note that we skip the first byte of the hybrid strings
 sprintf ((char*) &title [1], "File %s on %s (%.2fK)",
 (char*) &fileName [1],
 (char*) &volumeName [1],
 (double) size / 1024.0);
    // ‘title' is not yet a hybrid string, it has an undefined length byte
 title [0] = strlen ((char*) &title [1]);
}

Remember, you can't always get away with this. In the above we know that title, fileName and volumeName are non-const strings with room for 255 characters. Since ‘fileName' and ‘volumeName' will never be more than 63 and 27 bytes respectively, we're sure there is room to add the length byte to the end. Similarly, ‘title' won't break 130 bytes.

Damon Cokenias
<http://www.netgate.net/~cokenias>

 

Community Search:
MacTech Search:

Software Updates via MacUpdate

Latest Forum Discussions

See All

Can PokeMatch help you find love with Po...
The unofficial Pokemon GO companion app space has exploded almost as fast as the game itself over the last few weeks. Aspiring app developers, many of them working solo, have given us apps that locate Pokemon, keep track of the server status, and... | Read more »
How to get started with Prisma
If there's one thing people like to do more than taking pictures with their smartphones, it's tinkering with those photos in some way. Numerous apps have sprung up over the last several years that allow you to use filters and special effects to... | Read more »
6 Pokemon GO updates you can expect, acc...
Pokemon GO had a scheduled appearance at this year's San Diego Comic-Con for a while, but it was only relatively close to the show that it was upgraded to a spot in Hall H. That's the biggest venue at SDCC, one usually reserved for the largest... | Read more »
How to evolve Eevee in Pokemon GO
By now, almost everyone should be hip to how to evolve Pokemon in Pokemon GO (and if not, there's a guide for that). Just gather enough candy of the appropriate type, feed them all to the Pokemon, and evolution happens. It's a miracle that would... | Read more »
CSR Racing 2: Guide to all game modes
It might not seem like there are all that many ways to go fast in a straight line, but CSR Racing 2 begs to differ. [Read more] | Read more »
Bulb Boy (Games)
Bulb Boy 1.0 Device: iOS Universal Category: Games Price: $2.99, Version: 1.0 (iTunes) Description: Multi-award winning 2D point & click horror adventure about a boy with a glowing head. | Read more »
5 top free emoji keyboard apps
If we're not at peak emoji yet as a society, it feels like we definitely should be. The emoji concept has gone far beyond what anyone in Japan could have envisioned when the people there unleashed it on an unsuspecting world, but the West has... | Read more »
How to unlock more characters in Disney...
One of the big charms of Disney Emoji Blitz is seeing a wide variety of beloved Disney and Pixar characters transformed into smiling emojis. Even someone like the sneaky Randall from Monsters Inc., who probably never cracked a smile on film, is... | Read more »
Cubway (Games)
Cubway 1.0 Device: iOS Universal Category: Games Price: $1.99, Version: 1.0 (iTunes) Description: Cubway is a journey with an abstract story of lifecycle of rebirth, called Samsara. Guide the cube through the long way full of dangers... | Read more »
Colorcube (Games)
Colorcube 1.0 Device: iOS Universal Category: Games Price: $1.99, Version: 1.0 (iTunes) Description: Turn pieces and blend colours in this minimal yet visually stunning puzzler.Over 200 handcrafted and challenging levels. Features... | Read more »

Price Scanner via MacPrices.net

Apple’s 2016 Back to School promotion: Free B...
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, and... Read more
Apple refurbished iPad Air 2s available start...
Apple has Certified Refurbished iPad Air 2 available starting at $339. Apple’s one-year warranty is included with each model, and shipping is free: - 128GB Wi-Fi iPad Air 2: $499 - 64GB Wi-Fi iPad... Read more
13-inch 2.5GHz MacBook Pro available for $964...
Overstock has the 13″ 2.5GHz MacBook Pro available for $964.21 including free shipping. Their price is $135 off MSRP. Read more
External Keyboard Innovations For iPad Pro (1...
I’m an input device aficionado. With non-touchscreen computers, which includes all Macs, the keyboard and mouse or trackpad are the tactile points of interface between user and machine, and the... Read more
GSK Rheumatoid Arthritis Study Leverages iPho...
Global healthcare products company GlaxoSmithKline (GSK) says that since 2014 they have begun transforming the way they conduct research, by leveraging state-of-the-art digital technologies — a... Read more
Clearance 12-inch Retina MacBooks, Apple refu...
Apple has Certified Refurbished 2015 12″ Retina MacBooks available starting at $929. Apple will include a standard one-year warranty with each MacBook, and shipping is free. The following... Read more
13-inch Retina MacBook Pros on sale for up to...
B&H Photo has 13″ Retina MacBook Pros on sale for up to $150 off MSRP. Shipping is free, and B&H charges NY tax only: - 13″ 2.7GHz/128GB Retina MacBook Pro: $1199 $100 off MSRP - 13″ 2.7GHz/... Read more
13-inch 1.6GHz/128GB MacBook Air on sale for...
Amazon has the 13″ 1.6GHz/128GB MacBook Air on sale for $200 off MSRP for a limited time. Shipping is free: - 13″ 1.6GHz/128GB MacBook Air (sku MMGF2LL/A): $799.99 $200 off MSRP Their price is the... Read more
13-inch 1.6GHz/256GB MacBook Air on sale for...
Amazon has the 13″ 1.6GHz/256GB MacBook Air on sale for $200 off MSRP for a limited time. Shipping is free: - 13″ 1.6GHz/256GB MacBook Air (sku MMGG2LL/A): $999.99 $200 off MSRP Their price is the... Read more
Free iOS Business App notably* Helps Service...
PayStudio Inc. has introduced their new business app notably* 1.0, developed for iPhone and iPod touch. notably* was specifically developed to help service and trade professionals go digital and... Read more

Jobs Board

*Apple* Retail - Multiple Positions, Willow...
Job Description:SalesSpecialist - Retail Customer Service and SalesTransform Apple Store visitors into loyal Apple customers. When customers enter the store, Read more
*Apple* Evangelist - JAMF Software (United S...
The Apple Evangelist is responsible for building and cultivating strategic relationships with Apple 's small and mid-market business development field teams. This Read more
*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* Professional Learning Specialist - A...
Job Summary The Apple Professional Learning Specialist is a full-time position for one year with Apple in the Phoenix, AZ area. This position requires a high Read more
*Apple* Picker - Apple Hill Orchard (United...
Apple Hill Orchard, Co. Rte. 21,Whitehall, NY 9/7/16-10/228/16. Pick fresh market or processing apples Productivity of 60 boxes and 80 boxes processing fruit per Read more
All contents are Copyright 1984-2011 by Xplain Corporation. All rights reserved. Theme designed by Icreon.