Amiga questions you've always been too embarrassed to ask

[mc6809e]

Originally Posted by Mrs Beanbag

@mc6809e:

You can add numbers using the blitter much more directly than that, I thought that was the original intended purpose of fill mode - to propagate the carry bit.

I believe the original purpose of fill mode is to fill

And while the blitter can be used to do addition bit-by-bit, I don't think it's nearly as fast and direct as simply loading two blitter registers and letting Agnus add them in a couple of cycles.

In fact, three additions can be done very quickly by using A,B, and C in one blit.

[Mrs Beanbag]

Originally Posted by mc6809e

I believe the original purpose of fill mode is to fill

Well! You would think so! But answer me this, why does it fill from right to left, such that you have to use descending mode?

The way the fill mode works, you don't need to worry about bit-by-bit addition, fill mode already carries a bit along from right to left. You could do addition on huge blocks of data (and of arbitrary precision, 128 bit integers, 256 bit integers... 16000 bit integers, whatever). I haven't yet worked out exactly the sequence of blits and minterms you'd need to use but I'm sure it's possible.

[Jope]

Originally Posted by xArtx

When the power LEDs go out, do they both go off, or does one LED go off
giving the appearance of the single long LED just going half as bright?
Or does this behaviour change depending on the particular model keyboard?

Both LEDs are driven at the same time. Whether they dim or go off depends on the motherboard. From Rev6 of the A500 onwards they dim.

I also remember that there are red/green and green/orange colour
combinations, and wonder if that is tied to any particular models?

Just the age of the machine. Older machines = red power/green drive, newer machines are green power/orange drive.

[xArtx]

Originally Posted by roy bates

if one goes off they both go off if they didnt you would still see one on.
as far a know to set a led half bright just lower the voltage going to it.

as for the different coloured leds,and led is an led you can put any colour in there just like the manufacturer did.

The second part is whether they changed the colours arbitrarily,
or it was indicative of a different model.. such as 500+.
When a guru meditation happens does the power LED flash half as bright or something like that?

[Mrs Beanbag]

Oh does anybody know what happens exactly if you do a blitter fill with BOTH Inclusive and Exclusive mode bits set?

[xArtx]

Originally Posted by Mrs Beanbag

Oh does anybody know what happens exactly if you do a blitter fill with BOTH Inclusive and Exclusive mode bits set?

It sounds like you are able to try it.
I will guess the result is not both operations on the value data.


Not to detract, but one more question because I found the name of the demo recently...
Was it found out how Spaceballs is possible?

[TCD]

Originally Posted by xArtx

Not to detract, but one more question because I found the name of the demo recently...
Was it found out how Spaceballs is possible?

I'll just assume you mean http://pouet.net/prod.php?which=99 and then you can read about it here http://www.techradar.com/news/comput...tions-715166/2 (scroll down a bit)

[Toni Wilen]

Originally Posted by Mrs Beanbag

Oh does anybody know what happens exactly if you do a blitter fill with BOTH Inclusive and Exclusive mode bits set?

Normal exclusive mode fill happens.

[Jope]

Originally Posted by xArtx

The second part is whether they changed the colours arbitrarily,
or it was indicative of a different model.. such as 500+.

Not really arbitrary, at some point (around 1990) they just started shipping them with the green power led. Some people still got machines with red. There is not much to be assumed from the power LED to be honest, just a general idea about the age of the machine.

When a guru meditation happens does the power LED flash half as bright or something like that?

Yes, it flashes between bright and dim if the motherboard is of a revision that doesn't turn the LED off.

[xArtx]

Originally Posted by Jope

Not really arbitrary, at some point (around 1990) they just started shipping them with the green power led. Some people still got machines with red. There is not much to be assumed from the power LED to be honest, just a general idea about the age of the machine.

Yes, it flashes between bright and dim if the motherboard is of a revision that doesn't turn the LED off.

It's all good still.. If I'm drawing an animated Amiga, and want to be anal about
it as I do, then I don't want an impossible configuration.
It sounds like an Orange/Green combination where the power LED dims,
on an a500+ is a legitimate combination,
While Red/Green with power LED off for an a500+ is an impossible combination.
So I can go with the former.

Originally Posted by Toni Wilen

Normal exclusive mode fill happens.

Yay!

I'll just assume you mean http://pouet.net/prod.php?which=99 and then you can read about it here http://www.techradar.com/news/comput...tions-715166/2 (scroll down a bit)

I never understood how it appears to contain so much data.
Just when you think they are reusing something..
what appears to be new data just keeps coming. I'll have a read

[Mrs Beanbag]

Well I've been thinking all night about how to get the blitter to do block addition, and I'm sorry to say I don't think it's possible to get it to do ripple carry using fill mode. But looking at the schematic it was so close, only a couple more gates would have made it possible. The signal is even called "carry" which is maybe a clue.

BUT it is certainly possible to implement a Carry Save Adder fairly easily.
http://en.wikipedia.org/wiki/Carry-save_adder
So it should also be possible to get it to do multiply-accumulate.

[xArtx]

Here's one:
Jay Miner was supposed to have gone off to design the Atari Lynx.
I did a little research on it, and found it uses an embedded 68k,
and some other chips in a single package.
The homebrew community also have a flash cart for it to run their own software (including a GPS).

Does the Lynx have any special similarity to Amiga's?

Why the lack of Jay Miner's name on anything Lynx?
His name is mentioned relating to the Lynx when you research Amiga,
but not when you research the Lynx. Maybe is is around the time we lost him?

[T_hairy_bootson]

https://atariage.com/Lynx/history.html

The Lynx was originally conceived by engineers at Epyx in 1987, where it was called the Handy. Dave Needle and R.J. Mical, two of the Handy's creators, were also members of the original Amiga design team.

I also read somewhere that the original lynx developement systems were amigas, much to Atari managements dissapointment.

[TCD]

I think it might be this thread: http://eab.abime.net/coders-general/...tml#post688425

[Mrs Beanbag]

Originally Posted by mc6809e

It should even be theoretically possible to turn the blitter+copper into a processor that is Turing-complete using a similar technique.

Actually I was thinking about this, it would be trivial to implement Rule 110 (a Turing complete cellular automaton) using just the Blitter. Or at least, a finite number of steps of it. Then use the copper to repeat the process. Not sure how useful it is, but it's good enough as a proof.

[xArtx]

So I heard the Amiga has it's own port of UAE.
Where does it get Kickstart from?
Does it use it's own disk drive, or are drives emulated, and still use ADFs?
Can you launch the emulator again, from within the emulation?
Surely someone tried.

It would be interesting to run a benchmark program for each instance.
I imagine it would take a high end Amiga to emulate an Amiga 500.

[diablothe2nd]

Originally Posted by xArtx

So I heard the Amiga has it's own port of UAE.
Where does it get Kickstart from?
Does it use it's own disk drive, or are drives emulated, and still use ADFs?
Can you launch the emulator again, from within the emulation?
Surely someone tried.

It would be interesting to run a benchmark program for each instance.
I imagine it would take a high end Amiga to emulate an Amiga 500.

We cannot tell you where to get a kickstart from other than by pulling it directly from your real amiga or from Amiga Forever. The kickstarts are still copyrighted so supplying you with them would likely get EAB shut down. Google is your friend though

drives are emulated and disk images are in ADF form unless you're running from a real amiga which can do both ADF and the real thing

emulating Amiga ON Amiga is only needed when you're running AmigaOS 4.x MorphOS AROS etc from a non native amiga system like the SAM systems, G4's or X86 systems. you don't need to emulate the amiga when using the real thing. Although for some stupid reason OS 4.1 for Real PowerPC Amigas does indeed emulate

[diablothe2nd]

What were these parts of Xcopy for?:



The left one i know goes to 81, but why was the default 79?

what were the ones on the right under Sync used for? in the manual is says that Sync is for advanced users but doesn't say what it does or why we would use it?

[s2325]

If I remember correctly all my copies were copied to 79, not any further. Disk was not readable when something was wrong with 40th track. I don't know why, I was only gamer and still I am.

[demolition]

Originally Posted by diablothe2nd

We cannot tell you where to get a kickstart from other than by pulling it directly from your real amiga or from Amiga Forever. The kickstarts are still copyrighted so supplying you with them would likely get EAB shut down. Google is your friend though

I think he meant whether it was loading them from the HDD or if it could pull it straight from the real ROM. I have never seen UAE for 68k, but I wouldn't be surprised if it existed. You could also try to run DOS UAE inside PCTask if you need a reason to bang your head against the wall.

Originally Posted by diablothe2nd

What were these parts of Xcopy for?:
The left one i know goes to 81, but why was the default 79?

what were the ones on the right under Sync used for? in the manual is says that Sync is for advanced users but doesn't say what it does or why we would use it?

A normal Amiga DOS disk contains 80 tracks, 0 to 79, however most disks and drives can go higher than that. Most will do 82 tracks and a few can do up 84 tracks. Custom disk formats could use this extra space, and I'm guessing some originals do as a copy protection measure.

The sync word tells the Amiga where a track starts. When it reads a track off the floppy it has no idea where it starts and where it ends as it is just a circle. It will search for this sync work in the raw MFM stream which will then indicate the start of the track. Amiga DOS disks always use 4489 sync, but other syncs are sometimes used, mainly for copy protection usage. If a copy program tries to read a protected disk using the wrong sync it will probably not be able to read the track.

Originally Posted by s2325

If I remember correctly all my copies were copied to 79, not any further. Disk was not readable when something was wrong with 40th track. I don't know why, I was only gamer and still I am.

Track 40 contains the root block which contains information about the disk name, the files in the root etc. so this can be considered as the entry point to reading the disk. If it can't be read, the entire disk is unreadable by conventional means (like losing the partition table on a HDD).