Re: SuperCPU for my C64 and C128

On 27/07/2018 04:46, Mia Magnusson wrote:
> You argued against it being read only...

I didn't. I said the bus was bi-directional.

In the standard Super CPU it only has to worry about what memory 
requests it's sending, as soon as you use ultimax mode you also have to 
receive requests.

> ... and the Ultimax mode would be "great", and a replica of the
> existing SuperCPU would just be "good enough". :)

A replica of the SuperCPU with Ultimax would be great, a 65816 Ultimax 
without SuperCPU would not be good enough.

> well, to just bring up the hardware you don't have to get the first 4k
> to work. Once you have reached that stage, you can worry about the
> first 4k.

Right, but until you've got the first 4k working then Ultimax mode would 
be pointless.

Because until you start running software then you can't point vic at a 
bank where Ultimax would work.

You could jump through hoops if you really wanted to do Ultimax first, 
but you need to mirror the first 4k anyway.

> No, as you have no way of putting any code in that ram before you start
> the 65816, unless you already have reached some more steps in the
> development process

The ROM needs to be shadowed into RAM so you can run at 20mhz.

Whether you did this by attaching it directly into your FPGA image, or 
by reading it from the C64 at startup is down to you. During bringup 
then I'd go for the former.

> No, it takes longer time and is more expensive to make hardware debug
> features than to spend short periods of time writing small pieces of
> test code.

To start with maybe, but as soon as you hit a problem then you're 
scrabbling in the dark.

If you started off prototyping with 1541 Ultimate then you already have 
options for debugging.

>   It is enough to write code that does something super simple
> like adding two numbers to each other and store the result in another
> position.

That won't help you figure stuff out like why vic fetches are sometimes 
interfering with 65816 fetches.

> Did anyone actually use any of the extra keys on a C128 except for
> 40/80 and ASCII/CC (for the international models)?

The escape key is often used in examples of typing escape codes.

https://www.commodore.ca/manuals/128_system_guide/app-i.htm#I.2

> But anyways there were afaik no C128 software requiring the user to
> actually use those extra keys. So a C128 mode would work rather well
> also on a C64.

There is not much in the way of c128 software that exists anyway, but I 
would assume terminal emulators etc would take advantage of escape & tab 
keys even if no other productivity software does. Stuffing the C128 
KERNEL/BASIC/CHARROM into your design and then letting people run some 
software that uses the C128 MMU might be good enough for some people.

I am hoping for a c128 emulation on the ultimate 64 & I'd probably start 
off with that hooked up to a c64 keyboard. But that won't stop me trying 
to hook up a c128 keyboard to get all the keys.