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Forums > C64 Coding > Attempt to modify 1541 ROM.
2017-07-30 21:06
Flavioweb

Registered: Nov 2011
Posts: 341
Attempt to modify 1541 ROM.

I'm experimenting with some 1541 rom changes using VICE but some strange happen...
I changed just one byte in the rom to avoid rom check:

EB1F: 4C 71 EA  JMP $EA71       ; to error display

into
(8:$eb2a) d eb1f
.8:eb1f  2C 71 EA    BIT $EA71

it seems i succeeded to load it correctly into Vice.
But:
(8:$eb49) break eb1f
#1 (Stop on  exec eb1f) 
.8:eb1f  2C 71 EA    BIT $EA71      - A:C0 X:C0 Y:00 SP:01 N.-..I..     813155
(8:$eb1f) z
.8:ea71  A6 6F       LDX $6F        - A:C0 X:C0 Y:00 SP:01 N.-..I..     813158
(8:$ea71) z
.8:ea73  9A          TXS            - A:C0 X:01 Y:00 SP:01 ..-..I..     813161
(8:$ea73) z
.8:ea74  BA          TSX            - A:C0 X:01 Y:00 SP:01 ..-..I..     813163
(8:$ea74) z
.8:ea75  A9 08       LDA #$08       - A:C0 X:01 Y:00 SP:01 ..-..I..     813165
(8:$ea75) z
.8:ea77  0D 00 1C    ORA $1C00      - A:08 X:01 Y:00 SP:01 ..-..I..     813167

Why?
Where i'm missing the force again =P ?
2017-07-30 21:19
iAN CooG

Registered: May 2002
Posts: 1712
erm, are you seriously trying to modify the ROM by editing it with VICE monitor and hoping it will work?
2017-07-30 21:25
Flavioweb

Registered: Nov 2011
Posts: 341
Quote: erm, are you seriously trying to modify the ROM by editing it with VICE monitor and hoping it will work?

No, i edited in an external binary editor... then i reloaded it into vice...
But... even if i can see the JMP ($4C) changed to BIT ($2C) correctly using the monitor, the code seems to behave like if the $4C-JMP still here...
2017-07-30 21:27
iAN CooG

Registered: May 2002
Posts: 1712
ah ok. I tried the same and it works for me
(C:$e5d4) break 8:eb1f
BREAK: 1 8:$eb1f (Stop on exec)
(8:$eb1f) d
.8:eb1f 2C 71 EA BIT $EA71
.8:eb22 4C 49 FF JMP $FF49
(8:$eb49) z
.8:eb22 4C 49 FF JMP $FF49 - A:C0 X:C0 Y:00 SP:45 N.-..I.. 813159
but I started afresh, relaunching vice and resetting to trigger the breakpoint
2017-07-30 21:32
Flavioweb

Registered: Nov 2011
Posts: 341
Here is the file i'm testing:
https://www.dropbox.com/s/je2wattifvvd5js/dos1541-fw?dl=0

I also checked it using "cmp":
cmp -l dos1541 dos1541-fw
11040 114  54
2017-07-30 21:46
Angel of Death

Registered: Apr 2008
Posts: 168
Why don't you use the (well documented) sources made by Soci mentioned in this (Looking for tass sources.) thread? Just change them and assemble them as a raw data-file.
He even rigged the checksum routines to make them bootable when changed.
2017-07-30 22:31
Flavioweb

Registered: Nov 2011
Posts: 341
Quote: Why don't you use the (well documented) sources made by Soci mentioned in this (Looking for tass sources.) thread? Just change them and assemble them as a raw data-file.
He even rigged the checksum routines to make them bootable when changed.


Thanks, nice idea =)
Now i managed to make "my rom" work correctly into Vice:
- start vice
- set "no drive" selected
- load my rom
- set drive to 1541
- reset

It work.
Otherwise, don't.
2017-07-30 23:39
iAN CooG

Registered: May 2002
Posts: 1712
what do you mean by "Load my ROM"? don't you set it in rom settings? or with -dos1541 parameter?
2017-07-31 05:54
Flavioweb

Registered: Nov 2011
Posts: 341
I set it via menu. Load drive rom -> 1541.
But since i'm binary patching, i need from time to time, to load the rom to check what i'm doing.
Loading it directly via menu, without restarting vice and re-setting all drive config, seems don't work.
2017-07-31 19:32
soci

Registered: Sep 2003
Posts: 357
My guess is that the 1541-II is set as default and replacing the 1541 ROM makes no difference until you select the 1541 as the drive type.
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