[SNES] Chrono Trigger Patches

[Europia79]

I have literally patched thousands upon thousands of romhacks & translations and there is always a few "problem patches" with various kinds of issues. Probably the most common issue I think is simply that RHDN &/or the documentation has incorrect information & patching instructions. And I think that's possibly what I'm dealing with here.

https://www.romhacking.net/hacks/993/

I'm trying to patch Chrono Trigger Impossible for the SNES, and I want an exact byte-for-byte copy of what the author intended. So, these SNES patches sometimes require a 512 byte Header, and sometimes they do not. Most of the time, I can simply patch BOTH and see which ones doesn't work. However, in this case, they BOTH work, so I'm at a loss as to which one is actually correct here ?

The ips patch is 4415 bytes. The Headered version produces a difference of 1120 bytes with CRC-32 9892127E (header removed after patching), while the Headerless version has a difference of 1742 bytes with a CRC-32 of 31F48D0A. And between them, there's a 2715 byte difference.

Anyways, this question is both specifically referring to the Impossible mod, as well as all of Chrono Trigger hacks in general (since it's likely that I'm going to encounter this same issue with other CT patches).

Since I've noticed that CDRomance has prepatched ROMs, I was hoping someone here had the technical expertise to help out ?

Otherwise, it looks like I'll be forced to reference the IPS file format and write my own parser that counts the number of writes (in bytes) it's making and compare that with the above differences ?

Thanks,
Euro

Post automatically merged: Mar 6, 2025

Based on https://zerosoft.zophar.net/ips.php

And:

#!/bin/bash
file="patch.ips";
eof="454F46";

declare -i index=5;
declare -i count=0;
while true
do
    offset=$(xxd -ps -s ${index} -l 3 "${file}");
    index+=3;
    size=$(xxd -ps -s ${index} -l 2 "${file}");
    index+=2;
    data=$(xxd -ps -s ${index} -l 0x${size} "${file}");
    index+=0x${size};
    count+=0x${size};
    
    echo "--------------------";
    printf "index: '%x'\n" ${index};
    printf "offset: '%x'\n" 0x${offset};
    printf "size: '%x'\n" 0x${size};
    echo "data: '${data}'";
    echo "count: '${count}'";
    
    if [ -z "$data" ]; then break; fi;
done
echo "--------------------";
echo "count: '${count}'";
exit 0;

I'm guessing that the Unheadered ROM is the correct one to use ?
Despite the patching instructions saying to use a Headered ROM ?

 

[Europia79]

Okay, I modified my approach and things quickly become readily apparent & crystal clear:

#!/bin/bash
# cmp 'parent_baserom' 'hack' | wc -l
# smc_diff=1120;
# sfc_diff=1742;
ips_file="patch.ips";
sfc_file="Chrono Trigger (USA).sfc";
smc_file="Chrono Trigger (USA).smc";
eof="454F46";

declare -i index=5;
declare -i count=0;
declare -i sfc=0;
declare -i smc=0;
while true
do
    offset=$(xxd -ps -s ${index} -l 3 "${ips_file}");
    index+=3;
    size=$(xxd -ps -s ${index} -l 2 "${ips_file}");
    index+=2;
    data=$(xxd -ps -s ${index} -l 0x${size} "${ips_file}");
    index+=0x${size};
    count+=0x${size};
    
    if [ -z "$data" ]; then break; fi;
    
    sfc_string="";
    sfc_data=$(xxd -ps -s 0x${offset} -l 0x${size} "${sfc_file}");
    for (( n=0; n < (( 0x${size} * 2 )); n+=2 ))
    do
        if [[ "${sfc_data:$n:2}" == "${data:$n:2}" ]]
        then
            sfc+=1;
            sfc_string="${sfc_string}${sfc_data:$n:2}";
        else
            sfc_string="${sfc_string}--";
        fi
    done
    
    smc_string="";
    smc_data=$(xxd -ps -s 0x${offset} -l 0x${size} "${smc_file}");
    for (( n=0; n < (( 0x${size} * 2 )); n+=2 ))
    do
        if [[ "${smc_data:$n:2}" == "${data:$n:2}" ]]
        then
            smc+=1;
            smc_string="${smc_string}${smc_data:$n:2}";
        else
            smc_string="${smc_string}--";
        fi
    done
    
    echo "--------------------";
    printf "index: '%x'\n" ${index};
    printf "offset: '%x'\n" 0x${offset};
    printf "size: '%x'\n" 0x${size};
    echo "data: '${data}'";
    echo " sfc: '${sfc_string}'";
    echo " smc: '${smc_string}'";
    echo "count: '${count}'";
    
done
echo "--------------------";
echo "count: '${count}'";
echo "sfc: '${sfc}'";
echo "smc: '${smc}'";
exit 0;

 

[Graw]

The patch might strip the header or account for it. The header doesn't change anything except memory addresses. If it's byte for byte, then it's byte for byte.

 

[Europia79]

The patch might strip the header or account for it. The header doesn't change anything except memory addresses.

I already solved this issue.