#A1200 U.K. Stocks
11 messages in this thread
Take a look at a zorro-ii video board, I think the picasso will run in an
a2000. This is better than aga and is only 16 bit.
AGA has many limitations, resolution and colour depth. These could be added to
an add on card, this would be good in itself.
AGA also has alot of speed problems due to design constraints.
Firstly when you are running in the highest resolution in 256 colour or HAM-8
then the processor has hardly any time which it can access video memory. When
the dma bandwidth is saturated the processor and blitter can only access chip
memory during the border areas being displayed. A pcmcia card could be designed
that didn't have this limitation.
Secondly AGA uses planar video, chunky video is much faster. If you want to
plot 1 pixel on a 256 colour screen it would take 8 reads, 8 modifies and 8
writes. On a chunky screen it would be 1 read, 1 modify and 1 write. The reason
that doom clones have been thin on the ground on the amiga ( and they still
aren't as good as the pc ) is because the amiga doesn't have chunky video
modes. These could be implemented on a pcmcia card.
Thirdly if you want to display 24bit pictures then you have to convert to 256
colours or HAM8, both of these take quite a long time to do. If you could
display 16 or 24bit pictures then there would be another speed advantage.
Just because AGA is 32bit does mean that it is better than OCS/ECS which were
16bit, it doesn't mean that it is better than any 16bit video subsystem.
Quite a few people are buying tower cases for the amiga1200 that gives you
zorro-ii slots so that they can run picasso boards etc. they wouldn't bother if
it was slower than AGA, would they?
I must admit that putting a video board in the pcmcia slot does sound a bit
strange, but it would be an improvement.
I just wish that someone would be willing to put research into this. It might
be possible to get a zorro-ii board to work by attaching it to the pcmcia port.
It of course wouldn't be able to do dma and other things that are supported by
zorro-ii, but to support one specific board it could work.
Phill
I've found out why the micronik tower for the 1200 can't use zorro3
the 1200 cpu is 24 bit ,not 32bit like a real 68020
the 68ec020 is 24bit not 32bit,which zorro 3 needs,<a 32 bit cpu for DMA>
this bit of info was from the micronik faq from the internet which was in
german<i understood bits and peices of it …
In fact i'll post it here in entirety so someone can translate into english
Maybe that was one reason that it doesn't allow zorro3, however if you add a
processor upgrade you would then have a 32bit processor. It would be alot more
expensive to support zorro3 as its more complicated. Zorro2 isnt much more than
connecting straight to the processor, zorro3 needs alot more silicon to work.
Phill
from the design of the zorro3 bus,it needs 32bit dma for it to work
this is is the inly real reason it doesnot work in a 1200
Not exactly, zorro3 only needs to dma into other zorro slots or chip ram. chip
ram doesn't need 32bit addressing as it is only ever the first 2mb of ram. It
probably wouldn't be able to dma to the pcmcia, but again that doesn't need
32bit addressing. The zorro3 bus could internally dma to other cards without
getting anyware near the trapdoor slot. The design goal for zorro3 was that it
could be interphased to any processor and dmaing between zorro cards is not
seen on the chip bus.
If you read the zorro3 section of the hardware reference manual you would get a
better understanding. Basically a zorro2 implementation uses the raw signals of
the trapdoor port whereas zorro3 handles most of the processing itself and only
passes on what it can't handle (like dmaing to chip memory).
You don't need a 32bit cpu for zorro3 as there was a prototype 020ec machine
with a zorro3 bus in it ( I think some of them were sold off as part of the
auction process ).
Zorro3 would be expensive to add to an a1200, but not impossible. If you have
any contradictory evidence I would be interested, but don't beleive sales hype.
If someone has a zorro2 tower on sale and you say "well I would buy one if it
was zorro3" then they will tell you it is impossible. What they mean is that
they haven't done it yet and they wouldn't be able to make enough money on it.
If you could buy a buster chip the rest would probably be very easy, but you
can't buy them in big enough quantities and re-designing it would be a pig.
Actually this reminds me of my idea for a pcmcia video board, everyone says
this is impossible too. I wish I had the money to invest in developing one.
Phill
not impossible,but how would it be able to reroute the graphics display
as for me,i plan on getting the tower with either a retina z2 or picasso 2
card
Re-route the graphics display? what do you mean? I guess you are talking about
using the same monitor for amiga and graphics card. Don't they have an external
cable for this?
Phill
Yeah for reina cards….
but reeouting would still be necessary…unless i can have 2 displays active on
2 monitors….<ie. one amiga /one grafx card…>
That is one of the problems with the amiga, some cards support mixing of
amiga&other screens, some don't even support dragable screens.
I think most will support switching between amiga graphics and video board
graphics though.
Phill
The 020 used in the A1200 is a 32 bit processor. The 24 bit limitation is in
the address bus. It can only address 16 M, rather than 4 Gig.
Jim
Multitasking AmigaOS 3.1, Mac System 7.1 and Windows 3.11 (in one old A2000)
But if you added another processor you could have a zorro3 bus, most of the
towers allow you to add a processor board, why not just have a processor slot
for adding an 030/040 or 060?
You still wouldn't lose anything if it was zorro3 just that you would only be
able to use zorro2 cards only.
But when you upgraded your processor you would then be able to use zorro3 slots
( in fact you could probably have a few zorro3 slots mapped into the first
16meg of memory, I don't remember there being anything in the spec that said
that zorro3 cards HAD to be above 16meg ).
Phill