Mastering the B

bbc/electron apps, languages, utils, educational progs, demos + more
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VMSZealot
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Mastering the B

Post by VMSZealot » Mon Oct 01, 2018 6:37 pm

I’m pondering what, if anything, prevents a Model B from running Master software (specifically, I’m thinking of software like the recent port of Prince of Persia). I thought that the main difference between the B and the Master is the amount of memory and the MOS version. Is there anything that can be done to make the B more Master compatible?

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tricky
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Re: Mastering the B

Post by tricky » Mon Oct 01, 2018 7:02 pm

There are a few 65c02 instructions, the ADC is at a different address, but the main thing for POP I think is shadow ram.
On the Master, there is full control for video/cpu access to Shadow ram, but on the B/B+ the video can only ever access the original 32K.

RobC
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Re: Mastering the B

Post by RobC » Mon Oct 01, 2018 9:36 pm

VMSZealot wrote:
Mon Oct 01, 2018 6:37 pm
Is there anything that can be done to make the B more Master compatible?
There is the Integra-B board that adds some (most?) of the Master's functionality to the Beeb. However, I don't think it adds shadow RAM in quite the same way (I have an Integra-B board but it doesn't work :( ).

I have wondered about writing a Master emulator for the Pi co-pro. I'm sure this could run things like PoP but I've not had the time yet to take it further.

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kieranhj
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Re: Mastering the B

Post by kieranhj » Mon Oct 01, 2018 10:13 pm

Yes, unfortunately for POP specifically it uses SHADOW RAM to display one screen whilst drawing the other as the frame rate is highly variable and would flicker unplayably otherwise. It also uses an additional 76K of RAM (64K SWRAM plus 4K ANDY and most of 8K HAZEL.)

The screen draw routine is quite complex, which is why I kept the original Apple II double-buffered approach. I guess in theory it could be made single-buffered like the C64 version but that one uses hardware sprites I understand. Alternatively it could be possible technically to make a MODE 5 version for a Model B but this would still require a minimum of 64K SWRAM, which seems like a fairly rare configuration in the wild, and a ton of work.
Bitshifters Collective | Retro Code & Demos for BBC Micro & Acorn computers | https://bitshifters.github.io/

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