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Forums > CSDb Discussions > IEEE article on the c64 from 1985
2017-10-10 15:49
Kruthers

Registered: Jul 2016
Posts: 9
IEEE article on the c64 from 1985

Came across this and thought other people might find it interesting. There are a few things in there that I never heard before, like why the NTSC model changed from 64 to 65 cycles per line, why the drive was so slow, and a video "sparkle" bug on the original machines that actually triggered sprite collisions...

Anyway, enjoy:

https://spectrum.ieee.org/ns/pdfs/commodore64_mar1985.pdf
2017-10-10 19:27
JackAsser

Registered: Jun 2002
Posts: 1254
Thanks! Really nice read!
2017-10-10 20:55
Cruzer

Registered: Dec 2001
Posts: 920
Interesting and well-written.
2017-10-10 22:36
Oswald

Registered: Apr 2002
Posts: 4136
I've seen bits and pieces of this, what caught my eye is the diagram showing where sprite and gfx fetches happen. Looks like this info was out there since ages :) I was only aware of these fetch places since VIC article came out.
2017-10-11 20:46
ThunderBlade

Registered: Jan 2002
Posts: 49
Nice, thanks!
2017-10-12 07:03
ChristopherJam

Registered: Aug 2004
Posts: 703
Thanks, that was a really interesting read.

Scary to read that we very nearly only had 57 cycles per line to work with, with no CPU cycles whatsoever on bad lines with all sprites enabled.

There were at least three times as many ex Commodore personnel working at Ensonique than I'd realised, too - the ESQ1 beside my desk is an even closer relative to the C64 than I thought!
2017-10-12 09:01
Krill

Registered: Apr 2002
Posts: 914
Quoting ChristopherJam
Scary to read that we very nearly only had 57 cycles per line to work with, with no CPU cycles whatsoever on bad lines with all sprites enabled.
I've missed that bit when first reading the article, then spent a while to find it. The only reference i found is in the "Sprites: making animation easy" box: "Moving across the video line, you've got 63 microseconds to play with. I was going to use memory running at just under 2 MHz, meaning only 114 memory fetches per line — period."

Is this where you gleamed this information from? Very attentive reading! :)

In this context, it's quite lucky (for us) that they later changed the timing to have 126 memory fetches per line AND lacked the time to change the sprite circuitry. What good are 4 chars wide sprites if you have no CPU cycles left with all 8 of them enabled on a badline? :D

That said, i don't remember having consciously done any VIC tricks on a badline with all 8 sprites enabled, and the maximum number of sprites over FLI so far is 6, if i haven't missed or forgotten an update on that. Hmm...
2017-10-12 09:07
Krill

Registered: Apr 2002
Posts: 914
Addendum: 6 sprites over "full-width" (37 chars) FLI. I've just remembered Soul — which features 8 sprites over FLI, but the bitmap is narrowed down due to way too late DMA. :)
2017-10-12 09:13
Oswald

Registered: Apr 2002
Posts: 4136
Quote: Addendum: 6 sprites over "full-width" (37 chars) FLI. I've just remembered Soul — which features 8 sprites over FLI, but the bitmap is narrowed down due to way too late DMA. :)

or shifli from krestology which was first :P
2017-10-12 09:22
ChristopherJam

Registered: Aug 2004
Posts: 703
Quoting Krill
The only reference i found is in the "Sprites: making animation easy" box: "Moving across the video line, you've got 63 microseconds to play with. I was going to use memory running at just under 2 MHz, meaning only 114 memory fetches per line — period."

Yes, that and the following paragraph about dividing 8 sprites into the remaining 34 fetches, to get the 24 pixel wide sprite resolution.

Quote:
Very attentive reading! :)

Thanks! I spread it over a few days..

Quote:
In this context, it's quite lucky (for us) that they later changed the timing to have 126 memory fetches per line AND lacked the time to change the sprite circuitry. What good are 4 chars wide sprites if you have no CPU cycles left with all 8 of them enabled on a badline? :D

Exactly! But it's also nice having more than 14 cycles available on no-sprites badlines; there wouldn't have been enough time for full width FLI, or various bitmap stretchers.

Quote:
That said, i don't remember having consciously done any VIC tricks on a badline with all 8 sprites enabled, and the maximum number of sprites over FLI so far is 6, if i haven't missed or forgotten an update on that. Hmm...


I can't remember if anyone's opened borders on a badline with all sprites present?

But yeah, the only time I've so much as seven sprites plus FLI was for the unrestricted 16 colour mode in Reutastic, and that's only 36 MCM pixels wide even with an REU…
2017-10-12 09:25
Krill

Registered: Apr 2002
Posts: 914
Quoting Oswald
or shifli from krestology which was first :P
Firstie schmirstie… Didn't say Soul was first. :) And Krestology, oh my… if there ever was a demo benefitting from warp mode, this is it. :D
 
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