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V.B.X.E Questions


PixelCrunch

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Hey, everyone. I just discovered the V.B.X.E today, and I was wondering a few things about it.

1: Does it have multiple Bitmap layers? (Like the SEGA Genesis and Super NES)
2: Can it re-define the 1024-color palette Per-Scanline? (Like the D.L.I on the Atari 8-Bit Series)
3: How many sprites are supported on it? How big are the sprites?
4: Why isn't anyone making more use of it?!
5: Is there any software that'll allow me to convert images to be displayable on the V.B.X.E? Any software that'll allow me to draw images that'll be displayable on the V.B.X.E? (Preferrably Windows-based.)

Please let me know!

-PixelCrunch

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48 minutes ago, PixelCrunch said:

1: Does it have multiple Bitmap layers? (Like the SEGA Genesis and Super NES)

Not really. You can combine the VBXE overlay with the normal Atari ANTIC playfield, and the VBXE attribute map can barely function as a third bitmap layer, but those two aren't comparable to the main overlay layer which does 16-256 colors.

 

48 minutes ago, PixelCrunch said:

2: Can it re-define the 1024-color palette Per-Scanline? (Like the D.L.I on the Atari 8-Bit Series)

You can reprogram the DAC palette on the fly, but the 6502 is far too slow to do more than a handful of colors at a time. Also, it takes 3-4 writes to set one color (index/red/green/blue), so it is slower than changing a GTIA color. You could probably fit one full color update in horizontal blank. This isn't an expected way to drive the VBXE as the four palette banks are intended to be used instead.

 

VBXE does allow switching between the palette banks with either the extended display list (XDL) or the attribute map. No DLIs are needed.

 

48 minutes ago, PixelCrunch said:

3: How many sprites are supported on it? How big are the sprites?

VBXE only supports the same sprites as GTIA, there are no new hardware sprite capabilities. You have to emulate additional sprites with bitmap techniques, though it does have a blitter to speed this up.

 

48 minutes ago, PixelCrunch said:

4: Why isn't anyone making more use of it?!

Because people have to have a VBXE in order to run VBXE-based software, and it requires internal installation -- it doesn't just plug into the cartridge or PBI port. There aren't many people who have a VBXE-capable system outside of emulation.

 

48 minutes ago, PixelCrunch said:

5: Is there any software that'll allow me to convert images to be displayable on the V.B.X.E? Any software that'll allow me to draw images that'll be displayable on the V.B.X.E? (Preferrably Windows-based.)

The main overlay mode is 320x192 with 256 colors, byte per pixel. You can use any tool that can handle indexed color.

 

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9 minutes ago, phaeron said:

Not really. You can combine the VBXE overlay with the normal Atari ANTIC playfield, and the VBXE attribute map can barely function as a third bitmap layer, but those two aren't comparable to the main overlay layer which does 16-256 colors.

 

You can reprogram the DAC palette on the fly, but the 6502 is far too slow to do more than a handful of colors at a time. Also, it takes 3-4 writes to set one color (index/red/green/blue), so it is slower than changing a GTIA color. You could probably fit one full color update in horizontal blank. This isn't an expected way to drive the VBXE as the four palette banks are intended to be used instead.

 

VBXE does allow switching between the palette banks with either the extended display list (XDL) or the attribute map. No DLIs are needed.

 

VBXE only supports the same sprites as GTIA, there are no new hardware sprite capabilities. You have to emulate additional sprites with bitmap techniques, though it does have a blitter to speed this up.

 

Because people have to have a VBXE in order to run VBXE-based software, and it requires internal installation -- it doesn't just plug into the cartridge or PBI port. There aren't many people who have a VBXE-capable system outside of emulation.

 

The main overlay mode is 320x192 with 256 colors, byte per pixel. You can use any tool that can handle indexed color.

 

If the 6502 is too slow to do DAC writes, then what about the enhanced 65C816 CPU, With a higher clockspeed enabled? (1.78 MHZ -> 3.58+ MHZ)?

Also, I know about the Video Modes, but what Tools can I use in order to make it *Readable* for the XVBE, and my Altirra emulator?

 

Edited by PixelCrunch
CPU name corrected.
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3 minutes ago, PixelCrunch said:

If the 6502 is too slow to do DAC writes, then what about the enhanced 65C18 (I may have gotten the name wrong) CPU, With a higher clockspeed (3.58+ MHZ)?

Yes, an accelerated 65C816 can do more writes, if running code from fast RAM. Accesses to the VBXE are still done at slow 1.79MHz speed, so rewriting the majority of a palette bank each scanline is still not possible.

 

Also, to do this, you would now require both a VBXE and a Rapidus, which further reduces the number of people who can run this from only a handful to effectively non-existent.

 

3 minutes ago, PixelCrunch said:

Also, I know about the Video Modes, but what Tools can I use in order to make it *Readable* for the XVBE, and my Altirra emulator?

Don't have a link offhand, but I think there were a couple of VBXE image viewers written.

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Just now, phaeron said:

Yes, an accelerated 65C816 can do more writes, if running code from fast RAM. Accesses to the VBXE are still done at slow 1.79MHz speed, so rewriting the majority of a palette bank each scanline is still not possible.

 

Also, to do this, you would now require both a VBXE and a Rapidus, which further reduces the number of people who can run this from only a handful to effectively non-existent.

 

Don't have a link offhand, but I think there were a couple of VBXE image viewers written.

So, the V.B.X.E is forced to do data-transfers at 1.79 MHz, no matter what?

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20 minutes ago, PixelCrunch said:

So, the V.B.X.E is forced to do data-transfers at 1.79 MHz, no matter what?

VBXE replaces the GTIA, which is tied to the main computer bus. The only way that the 6502 or a 6502-replacement can talk to it is at 1.79MHz. Can't run the system bus faster without screwing up timing of the entire system (and essentially replacing the entire system).

 

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VBXE operations to it's own RAM can be at ~ 14 MHz.  Slowdown for blits can be due to access needed for video output including XDL and Antic (if it's using VRam), and the 6502 wanting to access it - though only 1 cycle of the possible 8 is lost.

 

Sadly there's no palette upload option which would have been real nice given that at VBXE speed it could have been done in under a scanline.

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17 hours ago, Rybags said:

VBXE operations to it's own RAM can be at ~ 14 MHz.  Slowdown for blits can be due to access needed for video output including XDL and Antic (if it's using VRam), and the 6502 wanting to access it - though only 1 cycle of the possible 8 is lost.

 

Sadly there's no palette upload option which would have been real nice given that at VBXE speed it could have been done in under a scanline.

So, the V.B.X.E can still do scanline-based palette updates? You just need to be careful about what colors you use?

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No, it can't.  One thing on my wish-list would be that ability, ie for it to do palette updates via the blitter.  But it can operate on the VBXE's Ram only.

 

So, in reality you have to do 768 load/store operations with the CPU.  In theory you could speed it up with brute force unrolled code using immediate loads but then you're looking at a bit over 4K of program space and 18 6502 cycles per palette entry.

Edited by Rybags
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1 minute ago, flashjazzcat said:

There are a number of methods. If you're using Altirra, put the file inside a DOS 2.5 or SDFS 'virtual folder'. Or make a disk image, format it SDFS, and put the file inside the image. 

SDFS "Virtual Folder" seems the easiest way to do it. How do I do it?

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It's possible, but probably wouldn't be done that way. It'd look much better to draw the overlay on top with the blitter, using a handful of palette colors freed up by reducing the main picture slightly.

 

Keep in mind, that background picture alone is more than 60K of data. Not a problem to store on the VBXE since it has 512K of memory, but it's two thirds of a single density disk. So while VBXE has plenty of graphics capability, streaming large quantities of image data can be impractical short of a banked flash cartridge or mass storage device (CompactFlash/SD).

 

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