Re: PET kernal routines

Thanks. I have already communicated with Bo Z about this, and looked at this same memory map. It is pretty detailed, but does not show any details for the kernel. I will keep looking.

But I might ultimately decide to just alter the program so it contains its own CRLF and does not need the one in the TIM routine.




-----Original Message-----
>From: Pete Rittwage <peter@rittwage.com>
>Sent: Apr 13, 2017 1:35 PM
>To: cbm-hackers@musoftware.de
>Subject: Re: PET kernal routines
>
>> Hello all; I am new to this forum and this is my first post.
>>
>>
>>
>> I am one of the very early PET buyers/users, but 'got out of' the
>> Commodore
>> world in 1985 when I sold my PETs, VIC-20 and C-64. Only more recently did
>> I
>> decide to relive some of my past by acquiring a PET model 2001-32B to do
>> demonstrations of early computers (along with my Altair 8800, COSMAC
>> "ELF",
>> etc), but so far I have only demonstrated BASIC. I wanted to add a little
>> machine language to the demo, and planned to use the "Upgrade ROM"
>> integral
>> Tiny Machine Language Monitor (TIM or MLM). I found a scan of the manual
>> for
>> the TIM, but it is the version that came with a cassette, presumably to be
>> loaded into computers that did not already have it in the ROMs. As far as
>> I
>> know, only the later PET ROMs had the TIM, while the VIC-20 & C-64 did not
>> have it. I don't know if the TIM manual I downloaded is for a version
>> intended for the early PETs, or for the later VIC & C-64 machines.
>>
>>
>>
>> Anyway, there is a short (18 byte) piece of ML code in the manual that
>> simply writes a bunch of characters to the screen. It is supposed to use
>> two
>> of the TIM's internal routines, called as subroutines; "CRLF" which I
>> believe simply does a 'carriage return/line feed' to move the cursor
>> position (screen pointer) away from the text already on the screen, and
>> this
>> is supposed to be at $04F2, and "WRT" at $FFD2 which writes the ASCII code
>> currently in the 6502's accumulator to the screen at the position of the
>> current screen pointer. The rest of the little program is basically just a
>> loop to increment the contents of the accumulator so that a different
>> ASCII
>> character is written in each screen position.
>>
>>
>>
>> My problem is that the program sends the PET into oblivion, apparently
>> because the first part of the program is a JSR to $04F2, to use the "CRLF"
>> routine, and I don't think the routine (or ANYTHING) is actually at that
>> location. Nothing there to send control back to my program. The Upgrade
>> ROM
>> version of the PET memory map shows that area of memory being unused and
>> available for RAM expansion. And it seems odd that for a 'tiny' monitor
>> program, two of its internal routines would be so widely spaced in memory
>> at
>> $04F2 and $FFD2.
>>
>>
>>
>> I NOP-ed the first three bytes of the program, eliminating the JSR to
>> $04F2,
>> and the rest of the program works fine.
>>
>>
>>
>> But I have had no success in finding any references to show where the
>> correct "CRLF" routine address is. I wonder if any of you might know of a
>> resource that would have this information. Ideally, a full list of the
>> kernel subroutines, especially those that are ostensibly part of the TIM,
>> or
>> at a minimum the location of the "CRLF" routine.
>>
>>
>>
>> Reference - here is the program in question. It resides in the second
>> cassette buffer at $033A.
>>
>>
>>
>> 033A      20 F2 04                JSR $04F2 ("CRLF" routine)  *** clearly
>> "CRLF" is not at $04F2, but WHERE is it? ***
>>
>> 033D      A2 20                     LDX $20 (load $20 into X)
>>
>> 033F       8A                           TXA (copy value from X to A so
>> subroutine can use it)
>>
>> 0340       20 D2 FF               JSR $FFD2 ("WRT" or "CHROUT" subroutine,
>> prints ASCII character from A onto screen at current screen pointer
>> location)
>>
>> 0343       E8                           INX (increment X)
>>
>> 0344       E0 60                      CPX $60 (compare X with immediate
>> value $60, to see if screen writing should stop)
>>
>> 0346       D0 F7                     BNE $F7 (if X does not equal $60, do
>> relative branch back to start of loop at $033F)
>>
>> 0348       00                           BRK (if X does equal $60, exit
>> loop
>> and return to TIM/MLM)
>>
>> 0349       4C 3A 03               JMP $033A (if 'go' command is again
>> typed
>> on TIM/MLM, program control returns to here, so jump to start of program)
>>
>>
>>
>> Thanks for any help with this
>
>
>Hi Paul,
>
>Well, 04F2 is in the middle of the beginning of RAM normally used by
>BASIC, so that would be very wrong for a KERNAL routine. I would grab an
>accurate KERNAL reference manual and memory map for the PET.
>
>Here is a good starting point:
>http://www.zimmers.net/cbmpics/cbm/PETx/petmem.txt
>
>-Pete Rittwage
>
>
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