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

Latest Forum Discussions

See All

Whitethorn Games combines two completely...
If you have ever gone fishing then you know that it is a lesson in patience, sitting around waiting for a bite that may never come. Well, that's because you have been doing it wrong, since as Whitehorn Games now demonstrates in new release Skate... | Read more »
Call of Duty Warzone is a Waiting Simula...
It's always fun when a splashy multiplayer game comes to mobile because they are few and far between, so I was excited to see the notification about Call of Duty: Warzone Mobile (finally) launching last week and wanted to try it out. As someone who... | Read more »
Albion Online introduces some massive ne...
Sandbox Interactive has announced an upcoming update to its flagship MMORPG Albion Online, containing massive updates to its existing guild Vs guild systems. Someone clearly rewatched the Helms Deep battle in Lord of the Rings and spent the next... | Read more »
Chucklefish announces launch date of the...
Chucklefish, the indie London-based team we probably all know from developing Terraria or their stint publishing Stardew Valley, has revealed the mobile release date for roguelike deck-builder Wildfrost. Developed by Gaziter and Deadpan Games, the... | Read more »
Netmarble opens pre-registration for act...
It has been close to three years since Netmarble announced they would be adapting the smash series Solo Leveling into a video game, and at last, they have announced the opening of pre-orders for Solo Leveling: Arise. [Read more] | Read more »
PUBG Mobile celebrates sixth anniversary...
For the past six years, PUBG Mobile has been one of the most popular shooters you can play in the palm of your hand, and Krafton is celebrating this milestone and many years of ups by teaming up with hit music man JVKE to create a special song for... | Read more »
ASTRA: Knights of Veda refuse to pump th...
In perhaps the most recent example of being incredibly eager, ASTRA: Knights of Veda has dropped its second collaboration with South Korean boyband Seventeen, named so as it consists of exactly thirteen members and a video collaboration with Lee... | Read more »
Collect all your cats and caterpillars a...
If you are growing tired of trying to build a town with your phone by using it as a tiny, ineffectual shover then fear no longer, as Independent Arts Software has announced the upcoming release of Construction Simulator 4, from the critically... | Read more »
Backbone complete its lineup of 2nd Gene...
With all the ports of big AAA games that have been coming to mobile, it is becoming more convenient than ever to own a good controller, and to help with this Backbone has announced the completion of their 2nd generation product lineup with their... | Read more »
Zenless Zone Zero opens entries for its...
miHoYo, aka HoYoverse, has become such a big name in mobile gaming that it's hard to believe that arguably their flagship title, Genshin Impact, is only three and a half years old. Now, they continue the road to the next title in their world, with... | Read more »

Price Scanner via MacPrices.net

B&H has Apple’s 13-inch M2 MacBook Airs o...
B&H Photo has 13″ MacBook Airs with M2 CPUs and 256GB of storage in stock and on sale for up to $150 off Apple’s new MSRP, starting at only $849. Free 1-2 day delivery is available to most US... Read more
M2 Mac minis on sale for $100-$200 off MSRP,...
B&H Photo has Apple’s M2-powered Mac minis back in stock and on sale today for $100-$200 off MSRP. Free 1-2 day shipping is available for most US addresses: – Mac mini M2/256GB SSD: $499, save $... Read more
Mac Studios with M2 Max and M2 Ultra CPUs on...
B&H Photo has standard-configuration Mac Studios with Apple’s M2 Max & Ultra CPUs in stock today and on Easter sale for $200 off MSRP. Their prices are the lowest available for these models... Read more
Deal Alert! B&H Photo has Apple’s 14-inch...
B&H Photo has new Gray and Black 14″ M3, M3 Pro, and M3 Max MacBook Pros on sale for $200-$300 off MSRP, starting at only $1399. B&H offers free 1-2 day delivery to most US addresses: – 14″ 8... Read more
Department Of Justice Sets Sights On Apple In...
NEWS – The ball has finally dropped on the big Apple. The ball (metaphorically speaking) — an antitrust lawsuit filed in the U.S. on March 21 by the Department of Justice (DOJ) — came down following... Read more
New 13-inch M3 MacBook Air on sale for $999,...
Amazon has Apple’s new 13″ M3 MacBook Air on sale for $100 off MSRP for the first time, now just $999 shipped. Shipping is free: – 13″ MacBook Air (8GB RAM/256GB SSD/Space Gray): $999 $100 off MSRP... Read more
Amazon has Apple’s 9th-generation WiFi iPads...
Amazon has Apple’s 9th generation 10.2″ WiFi iPads on sale for $80-$100 off MSRP, starting only $249. Their prices are the lowest available for new iPads anywhere: – 10″ 64GB WiFi iPad (Space Gray or... Read more
Discounted 14-inch M3 MacBook Pros with 16GB...
Apple retailer Expercom has 14″ MacBook Pros with M3 CPUs and 16GB of standard memory discounted by up to $120 off Apple’s MSRP: – 14″ M3 MacBook Pro (16GB RAM/256GB SSD): $1691.06 $108 off MSRP – 14... Read more
Clearance 15-inch M2 MacBook Airs on sale for...
B&H Photo has Apple’s 15″ MacBook Airs with M2 CPUs (8GB RAM/256GB SSD) in stock today and on clearance sale for $999 in all four colors. Free 1-2 delivery is available to most US addresses.... Read more
Clearance 13-inch M1 MacBook Airs drop to onl...
B&H has Apple’s base 13″ M1 MacBook Air (Space Gray, Silver, & Gold) in stock and on clearance sale today for $300 off MSRP, only $699. Free 1-2 day shipping is available to most addresses in... Read more

Jobs Board

Medical Assistant - Surgical Oncology- *Apple...
Medical Assistant - Surgical Oncology- Apple Hill Location: WellSpan Medical Group, York, PA Schedule: Full Time Sign-On Bonus Eligible Remote/Hybrid Regular Apply Read more
Omnichannel Associate - *Apple* Blossom Mal...
Omnichannel Associate - Apple Blossom Mall Location:Winchester, VA, United States (https://jobs.jcp.com/jobs/location/191170/winchester-va-united-states) - Apple Read more
Cashier - *Apple* Blossom Mall - JCPenney (...
Cashier - Apple Blossom Mall Location:Winchester, VA, United States (https://jobs.jcp.com/jobs/location/191170/winchester-va-united-states) - Apple Blossom Mall Read more
Operations Associate - *Apple* Blossom Mall...
Operations Associate - Apple Blossom Mall Location:Winchester, VA, United States (https://jobs.jcp.com/jobs/location/191170/winchester-va-united-states) - Apple Read more
Business Analyst | *Apple* Pay - Banco Popu...
Business Analyst | Apple PayApply now " Apply now + Apply Now + Start applying with LinkedIn Start + Please wait Date:Mar 19, 2024 Location: San Juan-Cupey, PR Read more
All contents are Copyright 1984-2011 by Xplain Corporation. All rights reserved. Theme designed by Icreon.