• Please review our updated Terms and Rules here
  • Exhibitor application for VCF West 2022 is now open! If you are interested in exhibiting, please fill out the form here.
  • Here are the results of the VCF East 2022 Post Event Survey: Survey Results

Cbm 2001 Pet strange boot

daver2

Veteran Member
Joined
Jun 19, 2012
Messages
6,890
Location
UK - Worcester
Read the manual?

The 16-bit checksum is a fundamental issue when it comes to EPROM programming. It can tell EPROM contents apart (as to what they contain), it can identify different revisions of the firmware, and it can detect if they become corrupt.

This concept is used within the PETTESTER (or I should say the accompanying documentation) to identify different versions of the Commodore PET BASIC ROMs and whether they are corrupt or not.

Dave
 

Nivag Swerdna

Experienced Member
Joined
Jul 17, 2020
Messages
360
Location
London, UK
Apologies. Our posts crossed. Looks like a Checksum-32 000039DB. That matches what I would expect so hopefully we are on the same page.

So Configuration CHARLIE uses rom 000039DB in UD9.

Can you take another screenshot... is it always the same?
 

Dave_C78

Veteran Member
Joined
Nov 25, 2017
Messages
1,786
So this is CHARLIE config with magicrom on ud9 socket:
 

Attachments

  • Schermata 2022-05-14 alle 15.56.46.jpg
    Schermata 2022-05-14 alle 15.56.46.jpg
    72.6 KB · Views: 5

Nivag Swerdna

Experienced Member
Joined
Jul 17, 2020
Messages
360
Location
London, UK
OK so what should have happened is "XYZZY" should be displayed in the top left hand corner and then it is read back and displayed in HEX down and to the right.

Can you take a photo of your character generator ROM and for good measure checksum it to prove it is good, please? Replace once done! Re-run the CHARLIE test and check nothing has changed.
 

Dave_C78

Veteran Member
Joined
Nov 25, 2017
Messages
1,786
This is Rom Char generator checksum: 00017B67
 

Attachments

  • Schermata 2022-05-14 alle 16.12.55.jpg
    Schermata 2022-05-14 alle 16.12.55.jpg
    81.6 KB · Views: 1

Dave_C78

Veteran Member
Joined
Nov 25, 2017
Messages
1,786
OK so what should have happened is "XYZZY" should be displayed in the top left hand corner and then it is read back and displayed in HEX down and to the right.

Can you take a photo of your character generator ROM and for good measure checksum it to prove it is good, please? Replace once done! Re-run the CHARLIE test and check nothing has changed.
ok nothing has changed!
 

Nivag Swerdna

Experienced Member
Joined
Jul 17, 2020
Messages
360
Location
London, UK
Once you have done the above.... we move on to Configuration DAVE which is the same as Configuration CHARLIE but with the 6522 VIA replaced at C5... please post a photo of the result

So Configuration DAVE is

UD9 contains Rom 000039DB in UD9 other ROMs (except CHARGEN) empty, with VIA installed

Checksum-32: 00017B67 is correct for characters-2.901447-10.bin. Whoot!
 
Last edited:

Dave_C78

Veteran Member
Joined
Nov 25, 2017
Messages
1,786
Ok this is DAVE config:
 

Attachments

  • Schermata 2022-05-14 alle 16.25.21.jpg
    Schermata 2022-05-14 alle 16.25.21.jpg
    158.7 KB · Views: 7

daver2

Veteran Member
Joined
Jun 19, 2012
Messages
6,890
Location
UK - Worcester
So, what’s wrong then...

Clue: The PETSCII codes for the letters ‘X’ and ‘Y’ are different, but they yield the same hex. result of 58 when read back...

Dave
 

Nivag Swerdna

Experienced Member
Joined
Jul 17, 2020
Messages
360
Location
London, UK
Ok this is DAVE config:
Interesting... so what it is meant to do is write XYZZY and then display 58 59 5B 5B 59 and we see 58 58 5B 5B 58 comparing the binary we conclude.. we lose the least significant bit is always being read as zero even when it should be set in the case of the Y character aka 59 aka 0101 1001 being read as 0101 1000. You've got (at least) one bit going missing on the way back!
 
Last edited:

daver2

Veteran Member
Joined
Jun 19, 2012
Messages
6,890
Location
UK - Worcester
It can’t be bad video RAM because (a) the initial PETTESTER character screen is correct and (b) the letters XYZZY display correctly.

Nivag, I suspect you may also have a bug in your own code for displaying the hexadecimal letters A through F?

Dave
 
Top