Amiga boot process

[pvc]

I was wondering if I could port some of my code to Amiga line of computers. It would give me a good opportunity to code for some vintage architecture; trying to reduce RAM usage as low as possible; implementing 'NOMMU' variants; testing my code against big endian arch; etc. But I have no idea how to build bootable floppy or hard disk image for these machines. I tried to analyze AROS source a little but maybe there is someone here who knows how to do that already

[bzt]

Hi,

I don't think examining AROS would do any good for you. It is not for the Amiga hardware, it is just an OS which provides the same interface towards user land as the original AmigaOS did. For one, Amiga hardware used M68k CPU, and AROS is available for x86 and PPC. The same stands for other forks too, like MorphOS and AmigaOne (the latter has its own special hardware).

As far as I know, the boot process differs for each Amiga. The 500 for example loads the first two sectors of a disk (very similar to BIOS boot), while the A1000 has kickstart code in ROM which does lots of things before it finally loads the boot sectors. I'm not expert on this topic, but it looks like there are many different versions of kickstart too.

Maybe this turns out to be helpful:
https://wiki.amigaos.net/wiki/Amiga_Flo ... ot_process
https://retrocomputing.stackexchange.co ... -workbench

Google is your friend and good luck

Cheers,
bzt

[iansjack]

There is an AROS port for Amiga hardware: http://www.evillabs.net/index.php/AROS_ ... iga_Status

[iansjack]

You might also like to check the NetBSD port: http://www.uk.netbsd.org/ports/amiga/

Although this only works on Amigas with an MMU, it might provide useful information about the boot process.

There's also a (discontinued) OpenBSD port: https://www.openbsd.org/amiga.html

Some more information here which should be useful, and point to further avenues of research: https://retrocomputing.stackexchange.co ... -workbench

And here you can find header files for the various bootblocks: http://amigadev.elowar.com/read/ADCD_2. ... e0554.html

And you'll want to look at the Amiga Hardware Reference Manual: http://amigadev.elowar.com/read/ADCD_2. ... e0000.html

[bzt]

@iansjack: why haven't I thought of that? Reading BSD sources is a great idea for this!

Cheers,
bzt

[jane477]

I was wondering if I could port some of my code to Amiga line of computers. It would give me a good opportunity to code for some vintage architecture; trying to reduce RAM usage as low as possible; implementing 'NOMMU' variants; testing my code against big endian arch; etc. But I have no idea how to build bootable floppy or hard disk image for these machines. I tried to analyze AROS source a little but maybe there is someone here who knows how to do that already

I was just wondering, were you successful in your attempt

[bloodline]

I was wondering if I could port some of my code to Amiga line of computers. It would give me a good opportunity to code for some vintage architecture; trying to reduce RAM usage as low as possible; implementing 'NOMMU' variants; testing my code against big endian arch; etc. But I have no idea how to build bootable floppy or hard disk image for these machines. I tried to analyze AROS source a little but maybe there is someone here who knows how to do that already

What code are you trying to port?

With the Amiga it's easy enough to create a bootable disk that drops you into the GUI environment, there you have a fairly standard CLI console to use your code. Fire up a decent emulator, like WinUAE, create a blank floppy image, then in the Amiga's command line type "install df0:", thats all you need to have a bootable floppy disk. Most of the cli commands are in the ROM so that makes things quite simple.

If you use a later ROM image (Kickstart 2.0+), then WinUAE can mount a directory as a hard disk in AmigaOS, and you can use that as an easy shared storage for getting thing into the Amiga environment.

I'd be happy to send you anything you need.

-Edit- If it's just the hardware you are interested in, then you just need to write your boot loader to the first two blocks (1024 bytes) of the floppy image, starting at offset 0xC (the first 12 bytes of block 0 have significance to the OS). There you need to set up the hardware (The ROM will have set up your interrupt vector table and organised the memory, so you can then use the value found at address 0x4 to access the kernel/executive function table), or you can go it alone. The hardest part for a new Amiga coder is that before any video will work you need to set up the display coprocessor using something called a "copper list" and allocate it some framebuffer RAM, if you are really interested, message me privately and we can work though it. My advice is just let the OS do all the hard work, the Amiga hardware doesn't really work like modern hardware and can take a little while to get your head around.

As far as I know, the boot process differs for each Amiga. The 500 for example loads the first two sectors of a disk (very similar to BIOS boot), while the A1000 has kickstart code in ROM which does lots of things before it finally loads the boot sectors. I'm not expert on this topic, but it looks like there are many different versions of kickstart too.

Only the Amiga 1000, had that weird two stage boot process, and that was due to the motherboard ROM being 64k... All other Amiga's had at least 256K ROMs (or larger), so were able to boot fully from a cold start.


There are only two ROMs worth using, Kickstart 1.3 (which was in the original Amiga500, so many many games expect it, but it lacks features one would expect in an Operating System now), and Kickstart 3.1 which was the last released by Commodore and is what AROS is a clone of, and provides what would now be considered the bare minimum features of a proper operating system.

[pvc]

Thanks, but unfortunately my 1200 died (probably something with Chip Ram and floppy drisk drive got flaky) and I, sort of, lost motivation. I've got some success with it but for now, nah. I am working on something else. Maybe I am going to resume this project when I get to fix my Amiga. I don't feel like working with emulator only.

[bloodline]

Thanks, but unfortunately my 1200 died (probably something with Chip Ram and floppy drisk drive got flaky) and I, sort of, lost motivation. I've got some success with it but for now, nah. I am working on something else. Maybe I am going to resume this project when I get to fix my Amiga. I don't feel like working with emulator only.

Ahhh, yeah the problem of ageing hardware. I don't have any compatible monitors to run my vintage hardware...

Feel free to drop me a line if you want to pursue this avenue in the future. (finally a topic on OSDev where I can actually help someone )

[Octocontrabass]

I don't have any compatible monitors to run my vintage hardware...

Which hardware? If it's old enough, it might output something resembling standard composite NTSC or PAL video, which you might be able to hook up to your TV. (My Amiga does, at least.) There are also upscalers that can handle such signals and convert them into something a modern monitor can handle. Don't be too surprised if there are compatibility issues, though.

I haven't figured out what to do with EGA yet.

[bloodline]

I don't have any compatible monitors to run my vintage hardware...

Which hardware? If it's old enough, it might output something resembling standard composite NTSC or PAL video, which you might be able to hook up to your TV. (My Amiga does, at least.) There are also upscalers that can handle such signals and convert them into something a modern monitor can handle. Don't be too surprised if there are compatibility issues, though.

I have one 10 year old 20” LCD TV packed away in the garage somewhere, which can accept an RF and Scart signal, I only kept it for use with my vintage hardware. But sadly I don’t have space to set it up, so it was packed away years ago, and after two house moves I’ve not seen it since (though it must still be in a box in the garage).

My daughter has a RaspberryPi in an A1200 case (with a Keyrah2) running Amibian, hooked up to her TV for playing games in her room. It’s almost impossible to tell that it isn’t just an ordinary Amiga with an HD.

I haven't figured out what to do with EGA yet.

Hmmm... Looking at the spec, the output does seem difficult