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Groups > comp.sys.apple2.programmer > #6083

Re: Typo in ProDOS refTechMan

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On 2023-08-24 2:06 a.m., Jerry Penner wrote:
> Colin Leroy-Mira <colin@colino.net> writes:
> 
> The P8 tech-ref states:
> 
> ---------------------------------------- SYSCALL  JSR MLI       ;Call
> Command Dispatcher DB CMDNUM     ;This determines which call is being
> made DW CMDLIST    ;A two-byte pointer to the parameter list BNE
> ERROR     ;Error if nonzero
> 
> Upon completion of the call, the MLI returns to the address of the 
> JSR plus 3 (in the above example, the BNE statement); the call number
> and parameter list pointer are skipped. 
> ----------------------------------------
> 
> Where the CPU returns to is 6 bytes past the label SYSCALL, which is
> the location of the "BNE ERROR" instruction.
> 
> I think I always read and understood the book the way I think Oliver 
> does, but I think the book's address arithmetic is wrong, looking at
> it now.
As far as I remember my 6502 assembly, when you do a JSR, the processor 
has already read the JSR byte and the two byte address so the PC is 
pointing at the DB CMDNUM statement and that is what is pushed on the 
stack.  The MLI pulls that address off the stack, adds 3 to it, pushes 
it back on the stack and does an RTS so that the BNE ERROR statement 
will get executed.

In other words, the SYSCALL is the address of the JSR but it isn't the 
address that gets pushed onto the stack when the JSR is executed.

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Typo in ProDOS refTechMan Colin Leroy-Mira <colin@colino.net> - 2023-08-22 22:19 +0200
  Re: Typo in ProDOS refTechMan Jerry Penner <jerry+a2@jpen.ca> - 2023-08-22 22:49 -0600
    Re: Typo in ProDOS refTechMan Colin Leroy-Mira <colin@colino.net> - 2023-08-23 08:23 +0200
      Re: Typo in ProDOS refTechMan Oliver Schmidt <ol.sc@web.de> - 2023-08-23 07:38 +0000
        Re: Typo in ProDOS refTechMan Colin Leroy-Mira <colin@colino.net> - 2023-08-23 15:22 +0200
          Re: Typo in ProDOS refTechMan Jerry Penner <jerry+a2@jpen.ca> - 2023-08-24 00:06 -0600
            Re: Typo in ProDOS refTechMan Jeff Blakeney <CUTjeffrey_blakeney@yahoo.ca> - 2023-08-24 08:10 -0400
              Re: Typo in ProDOS refTechMan Michael J. Mahon <mjmahon@aol.com> - 2023-08-28 06:45 +0000
                Re: Typo in ProDOS refTechMan Jeff Blakeney <CUTjeffrey_blakeney@yahoo.ca> - 2023-08-28 08:28 -0400
                Re: Typo in ProDOS refTechMan Michael J. Mahon <mjmahon@aol.com> - 2023-08-31 18:54 +0000
                Re: Typo in ProDOS refTechMan Peter 'Shaggy' Haywood <phaywood@alphalink.com.au> - 2023-08-31 13:30 +1000
                Re: Typo in ProDOS refTechMan Michael J. Mahon <mjmahon@aol.com> - 2023-08-31 18:54 +0000
                Re: Typo in ProDOS refTechMan Antoine Vignau <ntn.vignau@gmail.com> - 2023-09-07 12:41 -0700
                Re: Typo in ProDOS refTechMan Peter 'Shaggy' Haywood <phaywood@alphalink.com.au> - 2023-09-05 12:14 +1000
  Re: Typo in ProDOS refTechMan qkumba <peter.ferrie@gmail.com> - 2023-08-28 10:23 -0700
    Re: Typo in ProDOS refTechMan Antoine Vignau <ntn.vignau@gmail.com> - 2023-08-28 12:29 -0700

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