Re: Hardware emulation of 6509 using 6502?

Den Tue, 06 Mar 2018 22:56:52 +0100 skrev Michał Pleban
<lists@michau.name>:
> Hello!
> 
> Steve Gray wrote:
> 
> > There was a 24K ram cart for the CBM-II series. It adds 24K into
> > bank 15. I wonder if the P500 could use that ram for
> > graphics/sprites?
> 
> A good thing to check. I must pull my P500 from storage, and then I
> will try the cartridge.

By looking at the schematics, it's highly unlikely that the VIC-II
in the P500 can access that memory.


> > IMHO, Commodore should have fully populated BANK 15 with 64K ram and
> > made it possible to bank out the ROMs as the C64 does. This would
> > have made the machines 100 times more useful and would have allowed
> > large programs to run without all the overhead required to access
> > kernal routines from other banks.
> 
> Well, as I understand the idea was to have lots of big chunks of RAM
> available, and in bank 15 it's not so easy to do. Sure, you can bank
> out the ROMS and I/O chips C64-style but what's the point of going
> through such gymnastics when you have unrestricted access to RAM in
> banks 0-14? One of the points of expanding the address space to 1 MB
> was to get rid of huddling ROM and RAM in the same addresses.

One big question is if basic and machine code programs are slower than,
faster than or equal in speed to the C128?

> What they did really mess up, in my opinion, was the ability to call
> code across banks. With the 6509, it is a major pain and requires lots
> of setup, overhead and careful planning and code layout. They should
> have created an easy method of calling KERNAL from any bank (maybe by
> creating a 6509-specific instruction?) and this would allow for easy
> writing large programs utilizing several banks of memory.

Agree, they should have made some kind of "far call" stuff.



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