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Using the VBXE as a RAM expansion


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#1 morelenmir OFFLINE  

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Posted Sat Aug 11, 2018 5:54 PM

The VBXE is a surprisingly versatile mod. Not only does it produce amazingly gorgeous RGB video over a SCART lead, but it can be configured to act as a memory expansion and a soundcard of sorts. Given my XE seems to utterly refuse to run the U1MB and be stable at the same time, I am left relying on the VBXE to provide extra memory for SpartaDOS and so on. One--slight--downside to this setup is the type of expansion board the VBXE emulates is the 'Rambo'. Sadly this does not allow separate CPU/ANTIC access to the banked memory.

 

My questions are, would be it physically possible for the VBXE to be reconfigured to provide its extra RAM in the 'CompyShop' standard, which would support separated bank access? If so, is there any chance Candle would consider releasing a new core that did so?



#2 Rybags OFFLINE  

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Posted Sat Aug 11, 2018 6:41 PM

VBXE has the daughterboard for Antic so has all of it's signals physically available.

 

But for the full featured * core, at least 2 possible barriers to this:

1. I've been told that there's no room for further firmware/emulation additions.  One bug I reported is that in one of the GTIA modes (the colour only mode I think) the background colour is wrong.  There's also other features especially more versatile blitter that'd be desirable but for owners of the original and second release it's likely not to ever happen.

 

2. IO pins on the microcontroller are limited, the /HALT signal from Antic is needed to differentiate between CPU and Antic accesses and the /REF signal is needed to differentiate between Antic reads and refreshes.  I would guess there's a fair chance that neither are connected by default.

 

* noting there's also the VGA core and GTIA-only cores that would likely be extensible in the firmware at least.



#3 morelenmir OFFLINE  

morelenmir

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Posted Sun Aug 12, 2018 9:43 AM

That sounds like there is a very good chance it will prove impossible then... A real shame.



#4 flashjazzcat OFFLINE  

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Posted Sun Aug 12, 2018 11:11 AM

Sending the machine in for repair would be a much simpler solution.



#5 Rybags OFFLINE  

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Posted Sun Aug 12, 2018 6:12 PM

One thing the VBXE can do though is more memory quickly.

Rather than page flip to allow different segments of Ram to be seen by Antic you could just use the blit to move the entire 8K from one area to the active screen.

 

In a best case situation it'd take 18 scanlines.  More realistically it'd probably take about 25-50% longer but still a fairly easy task.

Of course the downside of doing that is that your software becomes incompatible with legacy machines.



#6 morelenmir OFFLINE  

morelenmir

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Posted Mon Aug 13, 2018 12:35 AM

Sending the machine in for repair would be a much simpler solution.

 

It may well come to that yet! Or just a flat out new machine--but they are not so easy to come by on eBay any more.

 

One thing the VBXE can do though is more memory quickly.

Rather than page flip to allow different segments of Ram to be seen by Antic you could just use the blit to move the entire 8K from one area to the active screen.

 

In a best case situation it'd take 18 scanlines.  More realistically it'd probably take about 25-50% longer but still a fairly easy task.

Of course the downside of doing that is that your software becomes incompatible with legacy machines.

 

An excellent idea!  I had not even thought about using the blitter in that way.  Previously I have felt that programming for the VBXE is extremely--and restrictively--difficult. I shall have to have a look at it again.



#7 Rybags OFFLINE  

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Posted Mon Aug 13, 2018 3:42 AM

The features compared to what I'd like are lacking, but it comes down to core space.  The wish list I have is stuff like array maths operations and doing bitshifts and masking on conventional graphics.

 

For my Quadrillion game I initially converted it to use Atari graphics format but a nasty bug or 3 crept in and I had to scrap it all and restart.

So I left the graphics largely alone and just used the blit to remap them to the linear from C= cell-based format.

 

You can even use blits to setup other blits, I did that in Moon Cresta to use the same blit list for draw and erase of the enemy sprites.

 

Really, VBXE is sufficiently fast that you could copy in an entire 16K bank in 40-50 scanlines, though you'd need to leave the memory alone until the operation finished.






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