A.D.A. Amiga Demoscene Archive

  Welcome guest! Please register a new account or log in

  

  

  

Demos Amiga Demoscene Archive Forum / Coding / Undocumented hardware features

 

Author Message
Blueberry
Member
#1 - Posted: 20 Jan 2008 17:46
Reply Quote
The discussion about blitter filling got me thinking: What undocumented features of the Amiga hardware are known? I seached a bit and found this thread:

http://eab.abime.net/showthread.php?t=19676

There are some really interesting pieces of information in there, especially about the copper and blitter line draw.

Anything else that people know about? Presumably the Amiga-on-a-chip guys have found out loads of interesting stuff as well.
TheDarkCoder
Member
#2 - Posted: 22 Jan 2008 12:37 - Edited
Reply Quote
Hi, as you may see I posted a question on that thread, but got no answer. :-(

About blitter line-mode I can confirm that the undocumented feature mentioned in that thread is true (this is the fact that BLTDPT is used only for the very first dot of the line). This allows to optimize line-drawing for filling, by letting the blitter plot the first dot on a invisible 1 word buffer. This is done by setting BLTDPT pointing to that buffer and BLTCPT to the real buffer.

My releated question is the following: in the thread Photon says (at least that's what I understend) it is possible to avoid blitting the last dot by decreasing by 1 the blitter height. That is correct, but according to my test does not solve the issue with polygon filling, because what is really needed is that no dots are written on the last row. Is there some other trick in Photon technique?

About undocumented features in general: I am very curious about the Ultra Hi res, the AGA guide mentions it but I didn't figure out how to make it work.
Blueberry
Member
#3 - Posted: 22 Jan 2008 21:10
Reply Quote
Yes, you are absolutely right. Just subtracting one from the length will not work. I took a look at my old blitter polygon line draw code, and I do it the "eor into first word" way. I think that is the most common.

I have also wondered about this ultrahires thing. It seems to be something that runs alongside the normal display, outputting... something... somewhere....
rload
Member
#4 - Posted: 23 Jan 2008 00:35
Reply Quote
where is the talk about ultra hires? Can there be more hi than super?
TheDarkCoder
Member
#5 - Posted: 23 Jan 2008 17:16
Reply Quote
@rload

the aga.guide, originally released by C= only to commercial developers,
mentions Ultra hi-res. It is activated by a bit in BPLCON0. It has 1 dedicated BPLPT and 1 dedicated BPLMOD. How it works? it's not described. Maybe it would have required special VRAM chips. There's some criptical phrase with VRAM in the guide. (VRAM probably means Video RAM: it was a special type of DRAM made by TI to be used for graphics purposes it was unsuccessful because it was more expensive than standard RAM). In the AAA specifications, it was stated that the hi-end AAA Amiga would have had better gfx capabilities thanks to VRAM.

Would it be nice if someone would reverse-engineer AGA to see what is inside the chips...
d0DgE
Member
#6 - Posted: 26 Jan 2008 03:21
Reply Quote
Dave Hayne to the rescue !!!11!
doom
Member
#7 - Posted: 28 Jan 2008 01:07
Reply Quote
I think people have been reverse-engineering AGA for a while now :), but only by experimenting. Cutting the chips open and trying to map them under a microscope, that isn't really realistic as far as I know. The cost would be extreme.

I seem to remember hearing that all the blueprints still exist, but they belong to some company that doesn't feel like sharing.
d0DgE
Member
#8 - Posted: 28 Jan 2008 15:58
Reply Quote
colanto ?
skan
Member
#9 - Posted: 12 Feb 2008 15:40
Reply Quote
d0DgE
colanto ?

do you mean "cloanto" maybe? ;)

and no, i guess that company is still Gateway2000 iirc
d0DgE
Member
#10 - Posted: 15 Feb 2008 11:04
Reply Quote
skan: OMG, you're right ... so I read/spelled this name wrong for more than 10 years /o\
I just presumed they got it because they own the KickROMs AFAIK (Amiga Forever)
skan
Member
#11 - Posted: 15 Feb 2008 11:06
Reply Quote
d0DgE

they don't "own" the KS ROMs, they just have a license to distribute'em along with AF package IIRC... :)

 

  Please register a new account or log in to comment

  

  

  

 

A.D.A. Amiga Demoscene Archive, Version 3.0