TweetFollow Us on Twitter

Debugging 1
Volume Number:10
Issue Number:1
Column Tag:Debugging

Ram Disks

Preserving data on RAM Disks via Macsbug

By Marek Hajek, Incline Village, Nevada

About the author

Marek Hajek has been programming the Macintosh since 1989. He programmed two and a half years for Sierra Software Innovations where he wrote several inhouse MacApp applications, participated in the development of SuperTEView, and the relational database engine - Inside Out II. Currently he is working on his bachelor’s degree in Computer Science and supports his education with contract programming. Your comments on this article are appreciated and can be sent to P.O. Box 7542, Incline Village, NV 89450.

This article is based on my experience with the product Maxima made by Connectix Corporation. I use Maxima to set up a RAM Disk on my Mac IIsi. If you are using a different RAM Disk software, consult its documentation to find out whether the RAM Disk is nonvolatile. This following information applies only to nonvolatile RAM Disks. What’s a nonvolatile RAM Disk?

Nonvolatile RAM Disks, Maxima included, have a peculiar characteristic about them. As long as power to the computer is not interrupted, the data on the RAM Disk is preserved. Restarts, shutdowns, and system crashes do not interrupt power to the RAM Disk and as a result the RAM Disk contents are preserved. On the other hand, if power is interrupted to the RAM Disk, its contents may become corrupted or wiped off. A power interrupt occurs when you reach in the back of your computer and press the power switch or someone trips over the power cord to your computer and pulls it out of the socket.

When a severe crash occurs because of a software bug, the goal is to restart your computer without having to use the power switch. This will preserve the integrity of your data. What is a safe way to restart your computer in the midst of a crash? The reset switch, that little two button box attached to the side of your computer, does a good job restarting a computer and does not interrupt power to the RAM Disk. Your RAM Disk data will be preserved every time you use the reset switch. Since the reset switch restarts a computer 99% of the time (I’ve seen bugs that disabled the reset switch), this article is mainly for those of you who either didn’t or can’t install one on your Mac. So, what are other “safe” ways to restart your computer when a crash takes place?

MACSBUG’S RS/RB - UNSAFE RESTARTING

Your Mac can be restarted with the Macsbug debugger (I assume you have Macsbug on your Mac). In the course of programming you’ve probably encountered the Macsbug display more than once. It usually shows up when a nasty bug occurs in your program. The usual way to restart your computer from Macsbug is to type in rs or rb followed by a return. Alas, sometimes the bug has done so much damage the Macsbug command rs or rb won’t work. This is the time when your probably reach in the back of the computer for the power switch. This definitely is not a safe way to restart the computer.

MACSBUG - RESTARTING the SAFE WAY

There is a safer way to restart your Mac from Macsbug. The step is simple. Set the PC (program counter) to point to the restart mechanism in ROM. The program counter keeps track the memory address of the next instruction that will be executed. How do you set the program counter? On my Mac IIsi the line I enter into Macsbug looks like this:

g 4080008C

The g means ‘go to instruction’ and 4080008C is the address of the instruction that will be executed next. The 4080008C is the IIsi’s ROM address where the code for the restart mechanism is located. Since it is in ROM, the code cannot be affected by software bugs and is safe to execute. Because your computer may have the restart mechanism at a different location in ROM than my IIsi, you need to find its address. This can be done by following the next 4 steps:

1) Save every open document and quit all running applications. After step number 4 you will have to restart your computer.

2) Enter Macsbug. I enter Macsbug using the key combination Cmd-Option-Power On Key. The Power On key has a little triangle pointing to the left and is usually located toward the top of the keyboard. If your keyboard doesn’t have the Power On Key, find another way to drop into Macsbug. There may be a different way to drop into Macsbug on your computer.

3) In Macsbug type in the next two lines, each line followed by a return. Don’t forget the ^ character (shift-6) after the closing parentheses on the first line!

PC = (Rombase)^ + 0A

S

4) Toward the bottom of the Macsbug window you should see something similar to the next two lines:

"No procedure name"

4080008C *MOVE #$2700,SR

The first number (4080008C on my Mac) under the line “No procedure name” is the address of the restart mechanism. Write it down somewhere safe. From now on, anytime a bug drops you into Macsbug and you want to safely restart your computer to save your RAM Disk data, enter the line “g 4080008C” into Macsbug, where 4080008C is the number you wrote down. To test whether this is the address of the restart mechanism, type g followed by a return into Macsbug. This should restart your computer. Next to the reset switch, using the Macsbug procedure outlined above is probably the safest way to restart your computer and safeguard the data on your RAM Disk.

 

Community Search:
MacTech Search:

Software Updates via MacUpdate

iFFmpeg 6.4.0 - Convert multimedia files...
iFFmpeg is a comprehensive media tool to convert movie, audio and media files between formats. The FFmpeg command line instructions can be very hard to master/understand, so iFFmpeg does all the hard... Read more
Beamer 3.3 - Stream any movie file from...
Beamer streams to your Apple TV.... Plays any movie file - Just like the popular desktop movie players, Beamer accepts all common formats, codecs and resolutions. AVI, MKV, MOV, MP4, WMV, FLV. To... Read more
jAlbum Pro 14.0 - Organize your digital...
jAlbum Pro has all the features you love in jAlbum, but comes with a commercial license. You can create gorgeous custom photo galleries for the Web without writing a line of code! Beginner-friendly... Read more
Apple Remote Desktop Client 3.9.3 - Clie...
Apple Remote Desktop Client is the best way to manage the Mac computers on your network. Distribute software, provide real-time online help to end users, create detailed software and hardware reports... Read more
Chromium 59.0.3071.109 - Fast and stable...
Chromium is an open-source browser project that aims to build a safer, faster, and more stable way for all Internet users to experience the web. Version 59.0.3071.109: This update has no Flash plug-... Read more
Thunderbird 52.2.0 - Email client from M...
As of July 2012, Thunderbird has transitioned to a new governance model, with new features being developed by the broader free software and open source community, and security fixes and improvements... Read more
Google Chrome 59.0.3071.109 - Modern and...
Google Chrome is a Web browser by Google, created to be a modern platform for Web pages and applications. It utilizes very fast loading of Web pages and has a V8 engine, which is a custom built... Read more
Shredo 1.2.2 - $9.99
Shredo is a beautiful, functional file-shredding and privacy scan utility. It permanently shreds files, folders, and external volumes' contents to keep information secure and impossible for anyone to... Read more
Airfoil 5.6.1 - Send audio from any app...
Airfoil allows you to send any audio to AirPort Express units, Apple TVs, and even other Macs and PCs, all in sync! It's your audio - everywhere. With Airfoil you can take audio from any... Read more
Vitamin-R 2.48 - Personal productivity t...
Vitamin-R creates the optimal conditions for your brain to work at its best by structuring your work into short bursts of distraction-free, highly focused activity alternating with opportunities for... Read more

Latest Forum Discussions

See All

The House of da Vinci (Games)
The House of da Vinci 1.0.0 Device: iOS Universal Category: Games Price: $4.99, Version: 1.0.0 (iTunes) Description: Enter The House of Da Vinci, a new must-try 3D puzzle adventure game. Solve mechanical puzzles, discover hidden... | Read more »
Solve the disappearance of history’s gre...
Blue Brain Games invites you to indulge in an immersive hands-on 3D puzzle adventure in similar vein to The Room series, with its debut release The House of Da Vinci. Set during the historic period of the Italian Renaissance (when Leonardo himself... | Read more »
Age of Rivals (Games)
Age of Rivals 3.3 Device: iOS Universal Category: Games Price: $.99, Version: 3.3 (iTunes) Description: Deep civilization-building strategy in a fast-paced card game! | Read more »
Panthera Frontier (Games)
Panthera Frontier 1.0 Device: iOS Universal Category: Games Price: $4.99, Version: 1.0 (iTunes) Description: | Read more »
Angry Birds Evolution beginner's gu...
Angry Birds changes things up a fair bit in its latest iteration, Angry Birds Evolution. The familiar sling-shot physics mechanics are still there, but the game now features team-based gameplay, RPG elements, and a new top-down view. With all of... | Read more »
Sega Forever is for the retro game fans
Sega is launching a new retro games service titled Sega Forever, in a move that's sure to delight games enthusiasts with a bit of nostalgia. Sega's releasing five classic games for free. The titles include Sonic the Hedgehog, Phantasy Star II,... | Read more »
The Little Acre (Games)
The Little Acre 1.0 Device: iOS Universal Category: Games Price: $2.99, Version: 1.0 (iTunes) Description: | Read more »
Lovely adventure game 'The Little A...
The Little Acre makes its way from PC to iOS today and it's a real charmer. It's a lovely little adventure game set in 1950's Ireland, gorgeously animated in a style slightly reminiscent of old Disney films. The game won a lot of praise for its... | Read more »
Futurama: Worlds of Tomorrow officially...
Futurama: Worlds of Tomorrow arrives next Thursday, and it features . . . Stephen Hawking? Turns out a few of your favorite science super stars, including Bill Nye, Neil DeGrasse Tyson, and George Takei will be making an appearance alongside the... | Read more »
MU Origin’s new update offers exciting c...
MU Origin is kicking off the summer with style. Its latest update is a real doozy, offering up plenty of fresh content. New challenges, some extra help for newcomers, and new costumes are just a few of the things you will find in the new patch. | Read more »

Price Scanner via MacPrices.net

Clearance 2016 MacBook Pros available for up...
B&H Photo has clearance 2016 13″ and 15″ MacBook Pros in stock today and on sale for up to $400 off original MSRP. Shipping is free, and B&H charges NY & NJ sales tax only: - 15″ 2.7GHz... Read more
Apple Ranks 9th In comScore Top 50 U.S. Digit...
comScore, Inc. has released its monthly ranking of U.S. online activity at the top digital media properties for May 2017 based on data from comScore Media Metrix Multi-Platform. * Entity has... Read more
10.5-inch iPad Pros available for up to $20 o...
B&H Photo has the new 2017 10.5″ iPad Pros available for up to $20 off MSRP including free shipping plus NY & NJ sales tax only: - 64GB iPad Pro WiFi: $649 - 256GB iPad Pro WiFi: $749 - 512GB... Read more
Three Off-The-Beaten-Track iOS Apps That Dese...
One of the great things about using iPads and iPhones is the vast selection of apps available for most anything you want or need to do. The three outlined in this article have been in my core app... Read more
Apple No. 1 Spot In Gartner Top 100 Vendors i...
Gartner, Inc. has unveiled the top global 100 vendors in IT in 2016 based on their revenue across IT (excluding communication services) and component market segments. In the Gartner Global Top 100:... Read more
Clearance iMacs available for up to $300 off...
B&H Photo has clearance 21″ and 27″ Apple iMacs available starting at $949, each including free shipping plus NY & NJ sales tax only: - 27″ 3.3GHz iMac 5K: $1999 $300 off original MSRP - 27″... Read more
1.4GHz Mac mini, refurbished, available for $...
The Apple Store has Apple Certified Refurbished 1.4GHz Mac minis available for $419. Apple’s one-year warranty is included, and shipping is free. Their price is $80 off MSRP, and it’s the lowest... Read more
Free Mixoo iOS Photo Editing App Gets Major U...
Button Software Technology has announced Mixoo 3.0, an important feature update to the company’s photo editor for iOS devices. Mixoo offers amazing ways to edit as well as decorate personal photo... Read more
FNable 2.0 Function Key Enabling Software Get...
Briksoftware has released FNable 2.0 With Touch Bar Support, a major new version of the function key enabling software now compatible with Touch Bar keyboards. FNable’s simplicity that allows users... Read more
Clearance 2016 12-inch Retina MacBooks, Apple...
Apple recently dropped prices on Certified Refurbished 2016 12″ Retina MacBooks, with models now available starting at $1019. Apple will include a standard one-year warranty with each MacBook, and... Read more

Jobs Board

*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
Security Data Analyst - *Apple* Information...
…data sources need to be collected to allow Information Security to better protect Apple employees and customers from a wide range of threats.Act as the subject matter Read more
Lead *Apple* Solutions Consultant - Apple I...
…integrity, and trust.Success Metrics/Key Performance Indicators:Quantitative* Year over Year growth in Apple Product and Beyond the Box sales in the assigned Point of Read more
*Apple* Solutions Consultant till v%u00E5r...
…ethics, integrity, and trust.Success Metrics/Key Performance Indicators:QuantitativeYear over Year growth in Apple Product and Beyond the Box sales in the assigned Point Read more
Sr. Software Engineer, *Apple* Retail - App...
Apple Retail is looking for a Software Engineer…You'll work on projects that touch all aspects of Apple Retail Point-of-Sale system, and will leverage your strong Read more
All contents are Copyright 1984-2011 by Xplain Corporation. All rights reserved. Theme designed by Icreon.