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Re: Is it possible to have the following words (RP@ RP! SP@ SP!) on hardware data and return stack

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On Mon, 16 Mar 2015 12:30:34 -0400, <mfanyikazi@gmail.com> wrote:

> I have a forth programming problem that is messing up my week , I am
> trying to port eforth's multitasker into a Forth CPU that has a hardware
> data and return stack. I don't know how to save and restore the stack
> pointers when the CPU uses hardware stacks.
>
> If anyone has a link or some documentation on how this can be done , or
> alternative Forth words to RP@ RP! SP@ SP! that allows the emulation of
> a context switching mechanism with forth please share , I will be much
> grateful to learn from you.

Where present, RP and SP return the address of the memory
location where the pointers to the return stack and data
stack are stored.  So, RP@ and SP@ should return the stack
pointers themselves and place them onto the data stack.
Of course, RP and SP are implemented in registers on most
implementations and therefore don't have an address.  This
is usually why RP and SP aren't present in most Forth systems.

Do RP@ RP! SP@ SP! work correctly for this eForth?

a) If so, you just need to execute RP@ and SP@ and then ! them
into some defined VARIABLEs or perhaps even into ALLOTed dictionary
space.  When the context switch is finished, you @ the variables
and use RP! and SP! to restore them.  If you're doing multiple
context switches, you'll need multiple sets of two variables,
i.e., an array, or perhaps a stack.

b) If not, then you'll need to implement RP@ RP! SP@ SP! as
"primitives" (or low-level words), likely using assembly. The
hardware stack pointers for the data and return stack should
or could be stored in registers.  So, you'd need assembly code
to push or pop both registers used for RP and SP to or from the
data stack.  You'll need to understand the code for eForth here
as well as the assembly for the Forth CPU that you're using.


Rod Pemberton

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Is it possible to have the following words (RP@ RP! SP@ SP!) on hardware data and return stack mfanyikazi@gmail.com - 2015-03-16 09:30 -0700
  Re: Is it possible to have the following words (RP@ RP! SP@ SP!) on hardware data and return stack jenfhaomndgfwutc@murmic.plus.com - 2015-03-16 17:13 +0000
    Re: Is it possible to have the following words (RP@ RP! SP@ SP!) on hardware data and return stack mfanyikazi@gmail.com - 2015-03-17 02:40 -0700
      Re: Is it possible to have the following words (RP@ RP! SP@ SP!) on hardware data and return stack Jan Coombs <Jan-54 <jenfhaomndgfwutc@murmic.plus.com>> - 2015-03-18 01:53 +0000
        Re: Is it possible to have the following words (RP@ RP! SP@ SP!) on hardware data and return stack rickman <gnuarm@gmail.com> - 2015-03-17 23:21 -0400
  Re: Is it possible to have the following words (RP@ RP! SP@ SP!) on hardware data and return stack albert@spenarnc.xs4all.nl (Albert van der Horst) - 2015-03-16 22:24 +0000
    Re: Is it possible to have the following words (RP@ RP! SP@ SP!) on hardware data and return stack rickman <gnuarm@gmail.com> - 2015-03-17 14:01 -0400
      Re: Is it possible to have the following words (RP@ RP! SP@ SP!) on hardware data and return stack JUERGEN <epldfpga@aol.com> - 2015-03-17 11:59 -0700
        Re: Is it possible to have the following words (RP@ RP! SP@ SP!) on hardware data and return stack rickman <gnuarm@gmail.com> - 2015-03-17 16:28 -0400
        Re: Is it possible to have the following words (RP@ RP! SP@ SP!) on hardware data and return stack anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2015-03-18 15:30 +0000
          Re: Is it possible to have the following words (RP@ RP! SP@ SP!) on hardware data and return stack Bernd Paysan <bernd.paysan@gmx.de> - 2015-03-18 22:12 +0100
  Re: Is it possible to have the following words (RP@ RP! SP@ SP!) on hardware data and return stack "Rod Pemberton" <buzz@notnotnontnooatno.cmm> - 2015-03-16 18:57 -0400
    Re: Is it possible to have the following words (RP@ RP! SP@ SP!) on hardware data and return stack mfanyikazi@gmail.com - 2015-03-17 02:52 -0700
      Re: Is it possible to have the following words (RP@ RP! SP@ SP!) on hardware data and return stack "Rod Pemberton" <buzz@notnotnontnooatno.cmm> - 2015-03-17 18:03 -0400
      Re: Is it possible to have the following words (RP@ RP! SP@ SP!) on hardware data and return stack anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2015-03-18 14:39 +0000
  Re: Is it possible to have the following words (RP@ RP! SP@ SP!) on hardware data and return stack mfanyikazi@gmail.com - 2015-03-17 02:58 -0700
  Re: Is it possible to have the following words (RP@ RP! SP@ SP!) on hardware data and return stack anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2015-03-17 16:48 +0000
  Re: Is it possible to have the following words (RP@ RP! SP@ SP!) on hardware data and return stack Lars Brinkhoff <lars.spam@nocrew.org> - 2015-03-18 12:16 +0100
    Re: Is it possible to have the following words (RP@ RP! SP@ SP!) on hardware data and return stack Lars Brinkhoff <lars.spam@nocrew.org> - 2015-03-18 12:43 +0100

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