Hi guys,

I'm writing a program that I would like to be compatible with the 6502 co-processor. What is the best way (i.e. fastest) way to output stuff directly to the screen?

Here is an example snippet of what I am trying to do:


Kind regards,

Francis.

Do you mean you want your code to reside in the co-pro memory ?

If in the co-pro memory then the above code won't work as the screen memory isn't in the co-pros memory, that's one reason why you've got lots of memory to play with on the co-pro side. To write to screen memory via the co-pro requires sending the bytes across the Tube interface. Which would slow things down a lot.

If your running in the beebs side then your above code would be ok.

If your running a graphic intensive program (i.e. a game) then getting the balance right between the two processors could be tricky.

Open Question : Did any other games apart from Elite make use of the co-pros faster processor ? I'd have thought a Chess game or anything where it's mostly computational work would have benefited, but sprite base games would not have fared so well.

Hi Steve,

I was just really wanting to be able to write to the screen memory regardless of whether the co-processor was active or not.

Maybe I'm just better forgetting about the co-processor compatibility.

Kind regards,

Francis.

I think the trend used to be to check for it, and if active inform user to switch it off before allowing the game to load. Otherwise it's a whole different machine if active.

I'm not at home just now so I can't consult my books for an answer, but how would you check if the co-processor is active?

In reference to your open question, did UIM make use of the co-processor? I can't remember, but it would be the only other likely candidate that I can think of.

Kind regards,

Francis.

Lifted straight from the advanced user guide;

Thanks Steve.

Kind regards,

Francis.

I've written the following code for the TUBE detection:

It works, but I can't help but feel that it could be done better.

I'm not sure about the <NEW VALUE>=(<OLD VALUE> AND Y) EOR X part. Is this necessary or can I just take the value in the X register only?

Kind regards,

Francis.

I've just removed lines 120-160 from the above listing and this also seems to work.

Kind regards,

Francis.

Yeah, you can just use the value returned directly in X

Thanks Rich!

Kind regards,

Francis.

For anyone that is interested here is the improved version of the TUBE detection code based on Rich's comments:

Kind regards,

Francis.

If you want to be executing in the I/O processor then your load and execution addresses have to be in the I/O processor.