Do you have a similar code paging macros for 4-page machine (16F877)?


>From: Don Hyde <DonH@AXONN.COM>
>Reply-To: pic microcontroller discussion list <PICLIST@MITVMA.MIT.EDU>
>To: PICLIST@MITVMA.MIT.EDU
>Subject: Re: [PIC]: Program Memory Paging
>Date: Mon, 16 Apr 2001 14:25:34 -0500
>
>I thought I would share a couple of macros I use to deal with code paging.
>These are for a 2-page machine (16C63 in this case).  For a 4-page machine,
>it is a bit more complicated.
>
>To use:
>
>         fcall   Subroutine_in_other_page
>
>or:
>
>         fgoto   Label_in_other_page
>
>Potential trap:
>
>DON'T do
>
>         btfsc   STATUS,c
>         fcall   Subroutine_call_you_meant_to_skip
>
>The fcall macro will create 3 lines of code, but the skip instruction will
>only skip the first of these!
>
>Note:
>         The MESSG line tells you if there's an unnecessary fcall, but I
>couldn't figure out how to get it to print the address in hex, so it's a
>pain to figure out where it happened.  MPLAB reports the error location as
>being in the macro file, so that's totally useless.
>The errorlevel 306 stuff suppresses the now-meaningless warnings about
>references to the other code page.
>Using the bsf and bcf leave the W register undisturbed, which means it can
>still be used to pass and return arguments.  This is especially important
>if
>you are using a call into the other page to do a lookup in a table or
>something.
>
>fcall macro t
>  If((t & 0x800) == ($ & 0x800))
>  MESSG   fcall not actually needed at #v($).
>  EndIf
>    If (t & 0x800)
>       bsf   PCLATH,3
>    Else
>       bcf   PCLATH,3
>    EndIf
>
>    errorlevel -306
>    call  t
>    errorlevel +306
>
>    If ($ & 0x800)
>       bsf   PCLATH,3
>    Else
>       bcf   PCLATH,3
>    EndIf
>  endm
>
>fgoto macro t
>  If((t & 0x800) == ($ & 0x800))
>  MESSG   fgoto not actually needed at #v($).
>  EndIf
>    If (t & 0x800)
>       bsf   PCLATH,3
>    Else
>       bcf   PCLATH,3
>    EndIf
>
>    errorlevel -306
>    goto  t
>    errorlevel +306
>
>  endm
>
> > -----Original Message-----
> > From: Olin Lathrop [mailto:olin_piclist@EMBEDINC.COM]
> > Sent: Monday, April 16, 2001 1:28 PM
> > To: PICLIST@MITVMA.MIT.EDU
> > Subject: Re: [PIC]: Program Memory Paging
> >
> >
> > > And, unless I am wrong, when you return from the CALL, you
> > need to set
> > > the PCLATH bits back to the value of the "calling" page -
> > although the
> > > datasheets are a little fuzzy about this.
> >
> > You don't need to, but I find it convenient to keep PCLATH
> > pointing to the
> > current code page.  PCLATH only matters when a GOTO or CALL
> > are executed, or
> > on an explicit modification of PCL.
> >
> >
> > ********************************************************************
> > Olin Lathrop, embedded systems consultant in Littleton Massachusetts
> > (978) 742-9014, olin@embedinc.com, http://www.embedinc.com
> >
> > --
> > http://www.piclist.com hint: To leave the PICList
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> >
> >
>
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