Re: 65C02 emulation

[bieling@terra.es]

Charlie Springer ha escrito:

> On Wed, 27 Dec 2006 21:26:55 -0800, bieling@terra.es wrote
> (in article <1167283615.114007.102690@79g2000cws.googlegroups.com>):
>
> > OTOH, if things are done this way, the burden of discriminating what
> > has to be read/written from/to the Apple II MLB, may happen to slow
> > down quite a lot the emulation speed of the "processor" ARM, but about
> > this I have not thought very much yet...?
>
> The ARMs have several memory access modes to handle full speed RAM and slower
> ROM and FLASH plus a mode that can hold till finished. So with the right MMU
> stuff one should be able to read/write at Apple bus speed when needed.

I didn't know. But please think about this very usual situation: a
program is running and doing useful things but at the same time is
polling the keyboard not *waiting* for a keypress but *checking* just
in case the user wants to halt it or whatever (control-c?). Your fast
processor is executing several tens of times faster that a regular 6502
would do, but everytime a keyboard poll apears in the program flow,
your superfast processor halts for at least 1000ns maybe up to 1999ns
because of it ? This has to be addessed somehow, don't you think so ?

> the program RAM and ROM space should be copied into fast RAM along with the
> emulator code. FLASH is too slow to use for anything but boot and resource
> storage.

Now Philips (NXP) claims that in their ARMs, code runs from the flash
at full speed.

>I will have to look closely at the current crop of MMU equipped ARM7
> and ARM9 chips. But I'm not going to worry about it till I can emulate the
> 6502 with the kind of speed I want.

I'd love to learn how are you doing it.

Regards,
Jorge Chamorro.