mccabe@hatteras.cs.unc.edu (Daniel McCabe) (04/21/91)
I keep hearing these reports that I can't have virtual memory beyond 16 MBytes in my Mac II because my ROMs aren't 32 bit clean (assuming that I've installed a PMMU in my Mac II). As far as I can tell, there is no technical reason to prevent my Mac II from having a large virtual address space, regardless of the ROMs. Am I wrong? My guess is that marketing considerations prevent this from happening. Why support old machines when you sell new ones, right? The beauty of virtual memory is that ALL of your memory can be virtual, not just your RAM. One possibility is to make your ROM virtual also. Simply load an image of a 32-bit clean ROM from your boot disk into RAM and remap the the virtual to physical address translation of the ROMs to the RAM containing the ROM image. I would be more than happy to eat 512K of real RAM in order to get large virtual memory. I shouldn't even have to upgrade my ROMs in hardware to get 32-bit virtual addressing. This should be doable completely in software. C'mon Apple. Do it right! Give all 020+PMMU and 030 machines the ability to really have 32-bit virtual memory instead of limiting them to a wimpy 16 MBytes! Any comments? Cheers, danm
c186bx@volga.Berkeley.EDU (Dan X. Filner) (04/21/91)
"danm" wrote : >The beauty of virtual memory is that ALL of your memory can be virtual, not >just your RAM. One possibility is to make your ROM virtual also. Simply >load an image of a 32-bit clean ROM from your boot disk into RAM and remap the >the virtual to physical address translation of the ROMs to the RAM containing >the ROM image. I would be more than happy to eat 512K of real RAM in order >to get large virtual memory. That is an excellent point - and a very comforting thought! No MAC with a PMMU need ever worry about ROM upgrades - unless... if devices on the NuBus were using hooks to where the ROMS were physically supposed to be then it wouldn't work too well. But I don't think that's the case... The terminology is a little misleading however - you wouldn't really be "Virtualizing" the ROMS - you'd only be mapping some RAM to where the ROMS really are... You couldn't really make the ROM's "virtual" since the virtual memory handler is probably going to rely on the code in the ROM's - you can't page your pager out, that's fer sure... Problems would seem to arise only in Legal form- if Apple were as easygoing with it's ROM upgrades as with the System then we could all rest happily... as I understand it Apple really, really, really doesn't like the idea of letting ROM's be copied/publicly available. Letting every mid-lifed Mac copy ROMS on a free-ware basis might sort of stick in their throats. I hope not. If anyone knows why this scheme wouldn't work, please let me(us all) know! Dan Filner c186bx@volga.berkeley.edu
hp48sx@wuarchive.wustl.edu (HP48SX Archive Maintainer) (04/21/91)
I am trying to use 16+ MB in my se/30 with IIsi ROM today. Is there anybody who knows what address the ROM uses ? I will then try to make a dump of it, and try playing with my '030 onboard PMMU. I guess it is just a hack that will take half an hour. But I need to know what address I can find the ROM on. BTW: You will always have to start up your machine from the original ROM, load the new ROM image, and then restart. But it may be worth it. Just waiting for another QD (quick and dirty) hack. Where are all those real programmers/hackers that existed 5-10 years ago ? I guess that high-level languages has spoiled the newer computer people. -- ******************************************************* Povl H. Pedersen hp48sx@wuarchive.wustl.edu HP48sx archive maintainer
CPS@cup.portal.com (CHRIS PATRIC SMOLINSKI) (04/22/91)
The ROM in a Mac sits at $400000. At boot time, it is temporarily mapped to $000000, (since the 680x0 starts execution there). Yes, there are a few hardware hackers left. I'm playing with a new found Lisa myself, and in a similar situation. I need to find the address of the ROM and various I/O (IWM, other ports) when the Lisa is in the "Service Mode". Trying to interface a 800K floppy drive. Good luck with your project, I'm a fellow SE/30 owner myself, rather annoyed with Apple's general attitude right now. - CHRIS
mccabe@hatteras.cs.unc.edu (Daniel McCabe) (04/23/91)
In article <1991Apr21.025813.5339@agate.berkeley.edu> c186bx@volga.Berkeley.EDU.UUCP (Dan X. Filner) writes: >unless... if devices on the NuBus were using hooks to where the >ROMS were physically supposed to be then it wouldn't work too well. >But I don't think that's the case... Accessing fixed locations within the ROM is verboten, because the locations might change from ROM to ROM. However, the MMU would map those accesses into the virtual ROM anyway. >The terminology is a little misleading however - you wouldn't really be >"Virtualizing" the ROMS - you'd only be mapping some RAM to where the ROMS >really are... >You couldn't really make the ROM's "virtual" since the virtual memory >handler is probably going to rely on the code in the ROM's - >you can't page your pager out, that's fer sure... I didn't intend to have the ROM's page out (although permitting it to swap would reduce the loss of real RAM). I would bet that you want to lock your virtual ROM into memory. >Problems would seem to arise only in Legal form- if Apple were as >easygoing with it's ROM upgrades as with the System then we could all rest >happily... as I understand it Apple really, really, really doesn't like >the idea of letting ROM's be copied/publicly available. Letting every >mid-lifed Mac copy ROMS on a free-ware basis might sort of stick in >their throats. I hope not. I am not advocating that users copy new ROM images. I am proposing that Apple ship a 32-bit clean ROM image with System 7. (You might quibble about the legal implications of that action, but I don't want to get into it). >If anyone knows why this scheme wouldn't work, please let me(us all) know! >Dan Filner >c186bx@volga.berkeley.edu Enquiring minds want to know. Cheers, danm P.S. I should have posted this disclaimer with my original message, but I forgot. No deception was intended. Therefore, I mention it at this time. Disclaimer: I am employed by a competitor of Apple. However, I have invested my personal funds in Apple's products. I don't want to reduce the value of that investment by letting Apple make my equipment obsolete.