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Mr SQL
Registered: Feb 2023
Posts: 158 |
C64 Compatibility with C128 in depth
Very educational video on 8-bit show and tell:
http://www.youtube.com/watch?v=Ial2VSAu7tw
Robin illustrates using the built-in dissembler/Editor Assembler to correct hotspots where the C128 is incompatible with the C64.
The C128 is still closely compatible for having enhancements to the same hardware. I remember when the CoCo III came out the GIME did not fully emulate the 6847 VDG creating more incompatibilities, particularly with the semigraphics modes.
Interesting commentary at the end of the video regarding the C64 mode being better for game development. |
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ws
Registered: Apr 2012
Posts: 251 |
Reminds me of a writeup i made in 2016, to remedy a bad experience with C=128 compatibility in 1988. Fuck copyprotections. |
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Mr SQL
Registered: Feb 2023
Posts: 158 |
Quote: Reminds me of a writeup i made in 2016, to remedy a bad experience with C=128 compatibility in 1988. Fuck copyprotections.
Excellent read I like that story! Very cool you were able to remove the copy protection changing only 5 bytes to bypass the checks AND the way you located #$C2 as the high byte to pass to the decryption algorithm searching for Nops,
I had a similar experience finally figuring out how remove copy protection from a program from 1987 in 2020. Felt like solving a crossword puzzle. |
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Fungus
Registered: Sep 2002
Posts: 746 |
That caps lock thing with switch sense line has got to be a bug in the rom.
The 1571 has many incompatibilities, I had many many games that would not load on it.
Particularly games with v-max v0/v1 from gamestar, some rapidlok titles.
With jiffydos it's even worse, only about 60-65% of my games worked with it. Many demos fail too. I ended up just removing the roms and selling them as they were mostly useless to me. |
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chatGPZ
Registered: Dec 2001
Posts: 11510 |
It's a good demonstration of why most knowledgeable people prefer written documentation over videos :)
Quote:That caps lock thing with switch sense line has got to be a bug in the rom.
No, the ROM works - its only his BASIC program that is broken :) |
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Mr SQL
Registered: Feb 2023
Posts: 158 |
Quote: That caps lock thing with switch sense line has got to be a bug in the rom.
The 1571 has many incompatibilities, I had many many games that would not load on it.
Particularly games with v-max v0/v1 from gamestar, some rapidlok titles.
With jiffydos it's even worse, only about 60-65% of my games worked with it. Many demos fail too. I ended up just removing the roms and selling them as they were mostly useless to me.
Sounds like the 1541 was the better option for compatibility. |
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Mr SQL
Registered: Feb 2023
Posts: 158 |
Quote: It's a good demonstration of why most knowledgeable people prefer written documentation over videos :)
Quote:That caps lock thing with switch sense line has got to be a bug in the rom.
No, the ROM works - its only his BASIC program that is broken :)
Written documentation is great, I particularly found the MOS 6581 datasheet and the C64 memory map most useful:
http://archive.6502.org/datasheets/mos_6581_sid.pdf
https://sta.c64.org/cbm64mem.html
I think overview videos are very useful too, I never know about those specific compatibility issues or the solutions until Robin illustrated them.
What errors did you spot in his BASIC program and why did they cause that compatibility issue? |
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chatGPZ
Registered: Dec 2001
Posts: 11510 |
Someone who claims to have written a cycle exact VCS emulator the runs on the C64 should have no problem to spot the problem in the program :) |
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Mr SQL
Registered: Feb 2023
Posts: 158 |
Quote: Someone who claims to have written a cycle exact VCS emulator the runs on the C64 should have no problem to spot the problem in the program :)
Well I wish you'd share your findings it sounds intriguing. I'm not as familiar with all of the nuances of the C64/C128 as with the Atari 2600. You wrote C64 and C128 emulators!
I like that ws shared his write-up of the copy protection bug he resolved. That would have been particularly difficult and time consuming to track down and I might not have been able to find the solution. |
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chatGPZ
Registered: Dec 2001
Posts: 11510 |
Spotting the problem in the basic program requires zero C64 knowledge, just basic programming 101 |
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Mr SQL
Registered: Feb 2023
Posts: 158 |
Quote: Spotting the problem in the basic program requires zero C64 knowledge, just basic programming 101
Very cool, in that case I'm glad you didn't give it away. I will take a look again and see if I can find it. |
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