MARIA POWER, 7800 MONSTER GRAPHIC CHIP Options

[ACE]

Sally is a CPU. Maria is a graphics processor.

Sally is the 'special' 6502 processor. I think the 'special' part is that it has some sort of halt line
or something to signal Maria. Something like that.

The Maria needs the 6502 only to build the list initially and then update only the necessary fields
for animations and color changes. If this were not the case, it would have further limited the time
available to the two chips to share the system between frames. The Sally would have needed to
recopy or rebuild a new list every frame. Instead a simple field update and list end mark is all you
need.

So there would be there's no way to switch between 7800 mode and 2600 mode for the sake of Sally to do graphics? I forgot that the Sally/Tia chases beams using missles to create graphics to screen. The Maria simply can't function like a CPU?

Maria is VERY similar to the OPL in the Jaguar. They both fetch instructions from a list and act
accordingly. The OPL is by far more flexible but it has its faults. The Jag OPL HAS to be copied
in and rebuilt everytime....I consider this another bad design choice.

The Maria does not destroy the list. That means you build it once then you update the needed
fields. The Jag needs to have a hard copy of the list, blit it to the list ram, update the necessary
fields every frame. This is one method.....there are many ways to approach a Jag OPL list.

I would have to assume, with that statement, that the Maria can't write anything to RAM for the TIA/Sally to read. Being that Maria runs a little faster then Sally, the Maria can somehow be used for other functions outside graphics. The Maria could write data to RAM for a brief moment and then be turned off for Sally to draw graphics based on what the Maria left-over. Or if the Maria can do some level of data manipulation in RAM, that would certainly give some level of flexibility. The advantage would be in Maria speed being 5 or 6 times faster then Sally so graphic wise, any flickering or artifacts won't be that noticable.

I remember you mentioning the 7800 in the "Put the 68k to sleep" wiki. Would the Maria be programmable like the Jag OPL? Not to say the Maria is like the OPL but is it (the Maria) programmable beyond just graphics if at all?

This post has been edited by ACE: Mar 15 2009, 03:33 PM

[ACE]

Just to give an update on my understanding of the Maria processor... It's been a while since I posted anything in this topic, but with the recent releasing of the new XM add-on from AA; thanks to Mr. Scavone for clearing up my understanding a while back, the maria is a peripheral and can't do any processing on it's own with out help from the CPU. So if there be any graphical manipulation of any kind, the CPU would have to manipulate the list that the Maria uses to display graphics. This boils down to list manipulation in the most extreme manner in order to make the most out of the graphics. My guess would be that scanline based graphics is the way to go with the Maria.

The thing I like about the 2600 way of producing graphics is the way the TIA uses missles by allowing the CPU to chase the beam before the pixel hits the screen. It seems very simple and very straight forward and there's even some rumor that the 2600 can handle graphics even faster when it isn't displayed to screen. The maria, on the other hand, needs a list which implies that this list would have to stream from a cartridge, to the CPU / RAM then to the Maria. once it hits the Maria processor, the CPU has to be halted while the Maria displays the graphics. That is really a shame in a way because while the Maria is displaying the graphics, the CPU can be doing something else, but it can't due to that halt procedure.

With more memory added to the XM add-on with more memory added, this will help to give more leverage for the CPU to do more stuff with more instruction. I look foward to the XM.

[ACE]

Here's a little theory that I'm sure isn't unfamiliar about that Atari 7800... Considering that the 6502 CPU runs at 1.79 mhz, with the Maria able to display graphics at 7.16; if prorammed properly, it's possible to capitalize on the 7800 CPU speed while allowing the Maria to display graphics without any slowdowns. The Maria can display a list so fast, the CPU can still get some breathing room to perform task provided you can tweak speeds between the Maria and the CPU. If you remember, when Maria is in use, the CPU has to halt until Maria is finished with what it's doing. Despite that the Maria doesn't display sprite maps or anything of that nature like the NES can and can only display a list, the advantage is that the CPU can act as a temporary blitter like function on a small scale provided that serious memory consideration is in order. After all the system only has 4kb or RAM to work with.