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Custom ROM Builder Tool--modified to work on alt 64 kernals
https://www.retrohackers.org/viewtopic.php?f=2&t=375		 Page 1 of 1
Author:  CadorBolin [ Sun Apr 06, 2008 7:40 pm ]
Post subject:  Custom ROM Builder Tool--modified to work on alt 64 kernals
Yesterday, I tried to use FMan's Custom ROM Builder Tool (from here: http://www.fooman.fi/computers/loader.php?doc=C64 under "Retro Replay ROMBuild") but whenever I tried to start my custom ROM from my MMC Replay, it would give me a blank screen--although I could start a program by pressing keys 1-8.

It turns out that the kernal in my C64 doesn't change the screen color RAM automatically by just clearing the screen--you also have to POKE 53281,x after the fact to make this visible as well. So I modified the assembly code for the Custom ROM Builder to work on my version of the 64 (about 1 in 3 C64s have this issue).

--------------------------------------------------
from the Changes-readme.txt file:

The original ROMBuild.cde did not work on my C64--mine had an
alternative kernal where the screen color memory did not change
until after the text was poked into the screen char memory.

So I modified the assembly code in ROMBuild.cde to show the menu
on my C64 with the different kernal. The only drawback is that
I didn't feel like recompiling, so I just changed the code
directly, so this version of the .cde does not allow you to
customize the screen colors.

The original version of the assembly code is in ROMBuild.cde.old

By: CadorBolin

Date: April 6, 2008

Attachments:
ROMmaker.zip [23.37 KiB]
Downloaded 1297 times
Author:  CadorBolin [ Fri Apr 11, 2008 9:36 pm ]
Post subject: 
I also created some custom ROMS with this tool. They can be flashed onto an MMC Replay (or Retro Replay I assume), here they are:

Utilities 1.bin:

80 column screen
Austro compiler
DIR designer
Dirty Sector Killer
Speedscript (word processor)
Sprite Machine
Supermon
Ultrafont

Utilities 2.bin:

Autoboot maker
Disk Demon sector editor
Handy Filer 64 (spreadsheet/database)
Koala Painter II
Sam Reciter (voice synthesizer)
Unscratch
Virtual Directory (to obtain the starting addresses of program files)
Wraptor 3.0 (disk archive tool)

8 Great Games.bin:

Ape Craze
Crossroads
Forbidden Forest
Froggee
Jupiter Lander
Minima Reloaded
Pakacuda
Wizard of Wor

Attachments:
custom ROMS.zip [155.51 KiB]
Downloaded 1277 times
Author:  zap [ Wed Apr 16, 2008 4:14 am ]
Post subject: 
Thanks mate will be trying them in a few hours.

Have Fun Shane
Author:  FMan [ Thu Jan 22, 2009 5:06 pm ]
Post subject:  Re: Custom ROM Builder Tool--modified to work on alt 64 kernals
CadorBolin wrote:
the screen color RAM automatically by just clearing the screen--you also have to POKE 53281,x

Well, the address 53281 is not really color RAM but the background color register. The background color is most definitely set by the code, so did you just write the wrong address?

Can someone confirm this issue? What is this alternative kernal and how is it known that one third of C64s have it? I could use some more precise information here, coz I have never heard of the color RAM being left as it is when performing CLS, and frankly it sounds like a 3rd party replacement KERNAL?
Author:  CadorBolin [ Tue Feb 10, 2009 4:13 pm ]
Post subject:  Re: Custom ROM Builder Tool--modified to work on alt 64 kernals
FMan wrote:
CadorBolin wrote:
the screen color RAM automatically by just clearing the screen--you also have to POKE 53281,x

Well, the address 53281 is not really color RAM but the background color register. The background color is most definitely set by the code, so did you just write the wrong address?

Can someone confirm this issue? What is this alternative kernal and how is it known that one third of C64s have it? I could use some more precise information here, coz I have never heard of the color RAM being left as it is when performing CLS, and frankly it sounds like a 3rd party replacement KERNAL?


There are 3 versions of the Commodore 64 kernal (pre-64C):

kernal.901227-01.bin 1994-06-11 8192
This 8-kilobyte 2364 ROM is the first revision of the Commodore 64 KERNAL. The RS-232 timing table is designed for exactly 1 MHz system clock frequency, although no C64 runs at that clock rate. Unlike later KERNAL revisions, this one does not detect the video system (PAL/NTSC). This KERNAL was probably only used in early North American Commodore 64 units.
kernal.901227-02.bin 1994-01-24 8192
This 8-kilobyte 2364 ROM is the second revision of the Commodore 64 KERNAL. It is the second most widely spread version.
kernal.901227-03.bin 1994-01-24 8192
This 8-kilobyte 2364 ROM is the third and essentially last revision of the Commodore 64 KERNAL. It is the most widely spread version.

I'm not sure which one that I have at home, but I notice that some programs do not display properly because of this.

A lot of programmers use the print"(color code)(clr screen)" trick to fill up the screen color ram with the 1000 color codes. My version of the c64 does not allow this, unless the screen color register is POKED after the fact.

It's a rather obscure issue, and it's hard to describe to someone unless they are there with me.
Author:  FMan [ Sun Feb 15, 2009 7:45 pm ]
Post subject:  Re: Custom ROM Builder Tool--modified to work on alt 64 kernals
Well, thanks for that information. It sure seems obscure if you somehow 'magically' get the colormap to show changes by writing to the background color register. Whatever this issue is, at this point it sounds more like something to do with hardware or perhaps even black magic...
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