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Re: WDC 65C832 design in today's world

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barrym95838 <barrym95838@yahoo.com> writes:

> On Friday, September 1, 2017 at 3:28:00 PM UTC-7, Antoine Vignau wrote:
>> Why? Because they are missing in the 65816
>> av
>
> There's no more op-code space, so you would have to start using $42
>  as a prefix byte to maintain any claim of backward compatibility.

An idea I had was to have a shadow memory for storing the upper two
bytes of 32-bit addresses.  As long as the shadow memory is all zero,
then 8-bit code will function normally.  But every instruction which
uses a two-byte address would also fetch two more bytes from the shadow
memory, constructing a four-byte address.  JSR would push the upper two
bytes of the return address to the shadow stack, and RTS would fetch
them.

You could have a status bit which you turn on/off to switch between
8-bit and 32-bit access, so that you can use regular 8-bit code in
ROMs.  You would need to be able to manipulate the shadow memory when
you load 32-bit code.  One way would be to have a mode where memory
reads come from the first 64k of regular memory, but writes go to the
first 64k of shadow memory.  After you set up the first 64k of shadow
memory (or as much of it as you need) you can turn on 32-bit mode and
JMP to it (or RET, or simply fall through to inline code) to bootstrap
program loading.

The nice thing about this scheme is the lack of bank registers and full
access to the 32-bit address space.  But you don't get any 16-bit
registers or any additional functionality.

Scott
-- 
Scott Hemphill	hemphill@alumni.caltech.edu
"This isn't flying.  This is falling, with style."  -- Buzz Lightyear

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WDC 65C832 design in today's world Anthony Ortiz <anthonypaulo@gmail.com> - 2017-09-01 11:14 -0700
  WDC 65C832 design in today's world Antoine Vignau <antoine.vignau@laposte.net> - 2017-09-01 13:12 -0700
    WDC 65C832 design in today's world Anthony Ortiz <anthonypaulo@gmail.com> - 2017-09-01 14:23 -0700
      WDC 65C832 design in today's world Antoine Vignau <antoine.vignau@laposte.net> - 2017-09-01 15:27 -0700
        Re: WDC 65C832 design in today's world barrym95838 <barrym95838@yahoo.com> - 2017-09-02 23:39 -0700
          Re: WDC 65C832 design in today's world Scott Hemphill <hemphill@hemphills.net> - 2017-09-06 13:02 -0400
          Re: WDC 65C832 design in today's world Anthony Ortiz <anthonypaulo@gmail.com> - 2017-09-06 11:13 -0700
            Re: WDC 65C832 design in today's world barrym95838 <barrym95838@yahoo.com> - 2017-09-06 15:58 -0700
            Re: WDC 65C832 design in today's world Steve Nickolas <usotsuki@buric.co> - 2017-09-07 02:08 -0400
    Re: WDC 65C832 design in today's world Brian Patrie <bpatrie@bellsouth.spamisicky.net> - 2017-09-03 07:20 -0500
      Re: WDC 65C832 design in today's world kelvin@pro-kegs.uucp (Kelvin Sherlock) - 2017-09-03 19:16 -0500
        Re: WDC 65C832 design in today's world barrym95838 <barrym95838@yahoo.com> - 2017-09-03 12:59 -0700
        Re: WDC 65C832 design in today's world James Davis <JPD.Enterprises@outlook.com> - 2017-09-03 19:00 -0700
        Re: WDC 65C832 design in today's world Michael J. Mahon <mjmahon@aol.com> - 2017-09-03 23:04 -0500
      Re: WDC 65C832 design in today's world James Davis <JPD.Enterprises@outlook.com> - 2017-09-03 18:56 -0700
  Re: WDC 65C832 design in today's world David Schmenk <dschmenk@gmail.com> - 2017-09-02 09:43 -0700
    Re: WDC 65C832 design in today's world Michael J. Mahon <mjmahon@aol.com> - 2017-09-02 12:50 -0500
      Re: WDC 65C832 design in today's world Anthony Ortiz <anthonypaulo@gmail.com> - 2017-09-02 13:05 -0700
        Re: WDC 65C832 design in today's world Jorge <jorge@jorgechamorro.com> - 2017-09-02 13:49 -0700
          Re: WDC 65C832 design in today's world Anthony Ortiz <anthonypaulo@gmail.com> - 2017-09-02 14:02 -0700
            Re: WDC 65C832 design in today's world David Schmenk <dschmenk@gmail.com> - 2017-09-02 14:43 -0700
      Re: WDC 65C832 design in today's world Michael J. Mahon <mjmahon@aol.com> - 2017-09-02 17:19 -0500

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