@xot that's how some DMA works. DMA does not always work like this on every system. Famously, the Sega Genesis featured something called Blast Processing, which is the ability for the 68000 and VDP to access the same bus at the exact same time during DMA, so you can write directly to the scanline during active scan to drive it at 8bpp, despite the Genesis only formally accepting 6bpp color.
@xot oh I very much consider myself a baby when it comes to computers. The ocean is too deep to ever reach the bottom lol.
On the Amiga, the whole system was built around simultaneous access, so DMA is split between time frames, even and odd. On even frames, the 68000 has bus access, on odd frames, the agnus chip has access. So they get around the bus access problem, kind of like preemptive multitasking in general.
@GabeMoralesVR@xot Unless you turn on 5 or 6 bit framebuffer mode, in which case wave good bye to your CPU cycles :-) It was a very clever machine indeed.
@GabeMoralesVR@xot Biggest mistake of that entire era for sure. I kinda understand why they did it (support for 8 color and 32 color modes) but still not worth it for the problems it caused.
@TomF@xot they were pretty much the norm back then, no? CGA, apple IIgs, Even in the console space, stuff like the sega master system and SNES used planar graphics too. Chunky graphics are obviously superior but it doesn't seem like until around 1990-ish that chunky took over, likely owing to ram finally falling enough in price.
I do like the cheap transparency tricks you can do with planar graphics tho.
@GabeMoralesVR@xot 32X was 256-colour palette byte-per-pixel, like VGA. Jaguar was very cool - a YUV style encoding that meant gouraud shading was very cheap. Atari Falcon finally got a 16-bit chunky mode - though very wide pixels. I forget if Amiga AGA was chunky or still bitplaned?
@GabeMoralesVR@xot Trying to think if anything had a chunky 16 color mode, i.e. two pixels packed in a byte. Would have been fascinating to compare to bitplanes in the 68k era.
@TomF@xot@TomF@xot AGA was still bitplaned, the CD32 had a chip called Akiko that was hardware chunky2planar conversion but it was slow.
The Sega Genesis is 4bpp byte packed, so 2 pixels per byte. Similarly, in index mode, the 32X processes at word length, so 2 bytes/16 bit as a time. So even though the framebuffer is 8bpp, it's read 2 pixels at a time, with a 1 pixel horizontal shift register for smooth scrolling. In both cases, you have to treat each chunky pack as 2 pixels.
@TomF@xot I actually love the Jaguar, I know the system has problems and it was severely cash starved, but it's like this fascinating train wreck that I honestly adore. I have a skunk board, the jaguar is a tech fetishist dream, so much parallel stuff happening. I unironically love the system, I think those games which used the low color mode in conjunction with heavy gouraud shading still look incredible, like Zero Five and obviously Tempest 2000.
@GabeMoralesVR@xot Yeah it was a brilliant idea by Flare - it was kinda evolved indirectly from the Spectrum, through the Konix Multisysyem! https://en.m.wikipedia.org/wiki/Flare_Technology
Some brilliant ideas - by far the biggest problem was the absurd number of bugs. Atari cutting ALL the corners, as usual :-)
@TomF@xot oh yeah, I'm familiar with the story, I have the official atari jaguar strategy guide put out by atari themselves, which is a fascinating read. Midway through the guide, I guess they gave up on actually writing a stragegy guide, and just info dumped a bunch of interviews and stuff from their last winter CES. So like, interviews with Jeff Minter and such. They have this long part with him where he talks about the Konix and Flare II and the creation of the Jag. Super cool stuff.
@TomF@xot There was this awesome synergy in game hardware back then, it was so much fun to follow the teams of people making these things instead of the companies. I love that the ZX Spectrum group lived on through the Jaguar, and similarly, I love how many Amiga alumni worked on the 3DO and later Nuon. The old guard of gaming that lived through those wild west days are real-deal heroes.
@TomF@xot To bring this around to your original post, I built one of those atari jaguar rotary controllers from a FAQ off of compuserve back in the day (@llamasoft_ox -- did you create the rotary joystick design yourself or was that something atari was going to eventually put out?)
Anywho, the same FAQ was a faq about the enhanced atari joystick port, and it included how there was a bug in the first revision of the jaguar, so the controller port has some features that nobody could reliably use
@GabeMoralesVR@TomF@xot the code for the rotary controller in T2K was basically made using a VCS driving controller as a basis, just in case they did decide to make an actual controller at some point after the game was released. It was done in the last days of final test of the game and I never had a chance to test it out with a real weighted controller, it was just "put it in there in case in the future someone can use it".
Add comment