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Offline Trev

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Re: Mac mini Os4
« on: January 24, 2008, 06:11:10 AM »
A more reasonable question would be, "How can I make my own bootable media?" The simple answer is you can't do it legally. The Open Firmware "second level bootloader," like the one written for U-Boot, is copyrighted, or at least not open source. (As an aside, I'm surprised. I've read that slb makes use of GPL code, but I don't know for sure.)

The good news is that if someone can reverse engineer the process and publish an open method for booting OS4 on Mac hardware, you're good to go in the US, as hardware for OS4 is no longer reasonably available. (Hey, the DMCA exemptions are good for at least some things.) You must, of course, own a copy of OS4. Now that the classic version is available, that shouldn't be an issue.
 

Offline Trev

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Re: Mac mini Os4
« Reply #1 on: January 24, 2008, 07:05:14 PM »
@downix

Quote
While the OF for U-Boot might be copyrighted, OF itself is an open standard, with GPL implimentations available. U-boot itself is GPL'd as well. This arguement is moot as a result.


Open Firmware and U-Boot are two separate pieces of software that serve the same purpose. The OS4 ELF bootloaders (both named slb) are different, and unless they were written with GPL code, they're not bound by the GPL itself.

Regardless, there's nothing stopping someone from writing an open (or closed) replacement bootloader for OS4 on the Mac Mini, PearPC, QuickTransit/Dynamite, or any other platform. The lack of available PowerPC "Amiga" hardware is a boon in that sense.
 

Offline Trev

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Re: Mac mini Os4
« Reply #2 on: January 24, 2008, 08:29:16 PM »
Writing the bootloader isn't the complicated part. The real effort is in writing device drivers to support the hardware on various platforms. There's a fairly dedicated OS4 crowd, though, so having an Open Firmware bootloader available may spur development.

Most likely, we'd see the same thing we saw with Amiga PCI busboards. At least with Macs, what you get per model is nearly universal--no worries about people writing drivers for hardware that's only generally available on second Saturdays at a rural Polish flea market.
 

Offline Trev

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Re: Mac mini Os4
« Reply #3 on: January 25, 2008, 07:10:23 PM »
All, the Moana bootloader (or whatever it's called) was never made legally public, so you shouldn't be having this conversation here. Not trying to play forum police, but you know, someone will come along and kill the conversation eventually.

A more constructive conversation would be an overview of what needs to be done to implement a new bootloader, either as a standalone ELF executable, a standalone Forth program, or some combination of the two. If anyone knows the ins and outs of the OS4 boot process, now's the time to chime in.
 

Offline Trev

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Re: Mac mini Os4
« Reply #4 on: January 25, 2008, 07:49:11 PM »
Now you've gone and killed the thread for sure. ;-)
 

Offline Trev

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Re: Mac mini Os4
« Reply #5 on: January 25, 2008, 10:47:12 PM »
Anyhow, it's probably hanging on initialization of a kernel module. If you're using one of the "debug" boot options (those that enable the serial port and set an appropriate debuglevel) and your iMac has a working serial port, you might get some useful information by connecting a serial console. The OS4 SDK might have information on debugging the boot process as well.
 

Offline Trev

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Re: Mac mini Os4
« Reply #6 on: January 28, 2008, 04:49:19 AM »
If you own a copy of OS4 and have a copy of the SDK, the documentation states pretty clearly how the OS4 boot process works. The rest requires a little bit of knowledge of how Open Firmware works. Everyhing you need to know has been spelled out in this thread.

And at some point, I imagine the ops will kill this thread. I'm being a pessimist, I know, but I'd really like to see a legitimate bootloader for PowerPC Macs out there, and this isn't the way to go about it.
 

Offline Trev

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Re: Mac mini Os4
« Reply #7 on: February 13, 2008, 06:57:34 PM »
No one's knocking the attempt, but the methods are dubious. The proper route:

1. Buy a copy of Amiga OS 4.
2. Learn the ins and outs of U-Boot.
3. Learn the ins and outs of Open Firmware.
4. Reverse engineer the U-Boot boot loader.
5. Write an Open Firmware boot loader.
6. Write device drivers for the target platform(s).

In general, the boot loader is going to do things like:

a. Initialize the hardware (MMU and whatever else OS4 requires).
b. Implement file system support (FFS, SFS, etc.). This could be done in Forth in Open Firmware or as part of the boot loader, which can be Forth, ELF, or anything else supported by the target platform.
c. Search for an appropriate boot device. The Moana boot loader uses an environment variable for this.
d. Read the layout file, which should include all necessary drivers.
e. Prompt for choices, if there's more than one.
e. Load the kernel per the layout file and user choice.

Open Firmware itself is open source and Forth is a well-established, well-documented, and proven language, so there shouldn't be any question about how to get generic information in those areas. The open source boot loaders for Linux and other operating systems ported to PowerPC Macs would be a good place to start for the Mac-specific stuff.

Writing device drivers is tricky, as the SDKs for some driver types, e.g. Picasso96 card and chip drivers, are not publicly available.