Amiga questions you've always been too embarrassed to ask

[eXeler0]

Originally Posted by Vot

Ram cost is the main reason for the design. Ram was expensive, the planar graphics was also to save ram.

So why wasnt the "tiled" -approach considered? (The SEGA Megadrives only has 64kB RAM and 64kB VideoRAM). There must be more than RAM cost alone behind the decision. It was probably a specific set of features they wanted it to have.. (IDK like maybe it was a good choice for TV stuff like Genlocks etc..)

[Vot]

Originally Posted by eXeler0

So why wasnt the "tiled" -approach considered? (The SEGA Megadrives only has 64kB RAM and 64kB VideoRAM). There must be more than RAM cost alone behind the decision. It was probably a specific set of features they wanted it to have.. (IDK like maybe it was a good choice for TV stuff like Genlocks etc..)

Read page 24 of chapter 2 in this book.

https://books.google.com.au/books?id...aphics&f=false

[eXeler0]

Originally Posted by Vot

Read page 24 of chapter 2 in this book.

https://books.google.com.au/books?id...aphics&f=false

Thanx, interesting - saved the book for later.. however that was the Planar vs Chunky argument. Tiled graphics are not really discussed on those pages.

[Vot]

Originally Posted by eXeler0

Thanx, interesting - saved the book for later.. however that was the Planar vs Chunky argument. Tiled graphics are not really discussed on those pages.

I cant comment on a tile based system other than memory efficiency is why they went planar and jay miner in retrospect regretted it.

Maybe they felt a full bitmap display and a blitter was a better generalised approach rather than tiled modes. I don't think i have read in any interview with Jay being asked about it unfortunately.

[ReadOnlyCat]

Originally Posted by eXeler0

Thanx, interesting - saved the book for later.. however that was the Planar vs Chunky argument. Tiled graphics are not really discussed on those pages.

It is useful to have a certain amount of fast access RAM for tiled graphics. The C64 does not use VRAM because its text/tile mode is low spec enough to not need it but the video processor still holds at least enough memory for a full line of tiles.

The MegaDrive takes advantage of this need to adjunct the video processor (VDP) with 64KB of VRAM so graphic modes do not slow down the processor as they do on the Amiga. So for a 16 bit machine it would have been logical to use VRAM for a tiled mode and thus for all other modes as well (to reduce complexity).

I suspect they did not want to make the Amiga even costlier by adding some additional VRAM to hold even just a line of tiles. The point of planar graphics after all is that they save memory when using low bitplanes modes.

[idrougge]

Why would tiled graphics cost more RAM bandwidth than bitmapped graphics? They still need to be drawn from RAM 50 times a second.

I think the simple reason that tiles weren't used is that bitmaps are more versatile, especially so if you're making a computer with a graphical operating system.

[Vot]

Originally Posted by idrougge

Why would tiled graphics cost more RAM bandwidth than bitmapped graphics? They still need to be drawn from RAM 50 times a second.

I think the simple reason that tiles weren't used is that bitmaps are more versatile, especially so if you're making a computer with a graphical operating system.

Especially when you can blit your own tiles ... Abet not as efficiently as if it was hardware implemented although.

[idrougge]

Absolutely not as efficiently. A tiled mode would have made the Amiga much more competitive once the 16-bit consoles were released, but what with Jay Miner having an Atari background and designing a new machine in 1983-84, it wasn't seriously considered.
Had the Amiga been released as the console it originally was designed as, a tiled mode would have saved a lot of memory, too.

[Vot]

Originally Posted by idrougge

Absolutely not as efficiently. A tiled mode would have made the Amiga much more competitive once the 16-bit consoles were released, but what with Jay Miner having an Atari background and designing a new machine in 1983-84, it wasn't seriously considered.
Had the Amiga been released as the console it originally was designed as, a tiled mode would have saved a lot of memory, too.

Im not sure it was going to be a console from early on. I think it was R.J talking in the history of the amiga video when he joined hi toro and he said the design had a keyboard and serial port etc etc.

[idrougge]

I think Mical or Luck talked recently about how a console version could have been speced with a minimum of RAM, utilising Paula's AM synthesis for sound and a low amount of bitplanes combined with sprites. That would have made sense for the kind of games en vogue at that point in time.

[ReadOnlyCat]

Originally Posted by idrougge

Why would tiled graphics cost more RAM bandwidth than bitmapped graphics? They still need to be drawn from RAM 50 times a second.

I think the simple reason that tiles weren't used is that bitmaps are more versatile, especially so if you're making a computer with a graphical operating system.

Re-read what I said.

You need less bandwidth overall because each tile encodes less colors than the palette used by the graphic mode but it is useful to cache a full line of tile because each tile is several pixels high and it is simpler to fetch it in one go rather than fetch each line of it separately. Especially with architectures which have column scrolling.

That is where VRAM can be useful because it can act as a fast speed cache of tiles and sprites even if your memory bandwidth is low.

Cf the MegaDrive which does exactly that.

VRAM is not strictly needed but even a line cache of tiles would have a massive cost impact on Agnus/Denise.

[idrougge]

While tiles with separate colour maps is clever and saves memory, I never thought of it in an Amiga context. I still don't see why a plain tilemap should eat any more DMA than a plain bitmap, unless the time required to "seek" the next tile in chipmem costs too much.

The X68000 had a small separate static RAM for sprite support due to this, I gather.

[ReadOnlyCat]

Originally Posted by idrougge

While tiles with separate colour maps is clever and saves memory, I never thought of it in an Amiga context. I still don't see why a plain tilemap should eat any more DMA than a plain bitmap, unless the time required to "seek" the next tile in chipmem costs too much.

The X68000 had a small separate static RAM for sprite support due to this, I gather.

Indeed, tile systems use as much or less memory bandwidth than bitmaps.
Sorry if this was not clear in my posts.

And more often than not, it's less. With a cache, they can use even less bandwidth when tiles repeat often because the corresponding RAM fetches are not needed anymore.

[s2325]

Is Amiga Master Axe and Karate Tournament had same graphician? [ Show youtube player ]

[eXeler0]

Is there any reason for a Kickstart 2.05 (from an A600) *not* to work on an A500 rev5 board? (if I do a "jumper hack" i.e. wire between pins 1-31 , + 21 to 31 on ROM chip and leg 31 bent outwards from the socket)?
And the follow-up question.. what exactly does the "jumper hack" do?

(I asked this in another more obscure place, but no answers so far)

[dJOS]

You don't need to hack anything for 2.05 or 3.1 Rom's to work in an a500.

[eXeler0]

Originally Posted by dJOS

You don't need to hack anything for 2.05 or 3.1 Rom's to work in an a500.

Well I tested it and it didn't work...
That's why I started googling for solutions (finding the above mentioned hack) and later posting questions here. The Rev5 board originally came with 1.2 which works fine but with the 2.05 ROM I just got garbage output. And the 2.05 ROM worked fine in the A600 before.

[dJOS]

Ah sorry I missed that you have a rev 5

[HardStep]

Can you make PCMCIA on A600 and A1200 bootable? With custom Kickstart?

[idrougge]

Kickstart supports booting from SRAM cards.

Booting from flash cards with a custom Kickstart should be feasible since there's a software patch for that included with CFD.device.