[ASM & Hex] How exactly is the trainer/secret id stored on a pokemon?

[tkim]

So I haven't a clue how the trainer/secret id is stored on a pokemon, and my goal here is to be able to use a custom trainer/secret id for the pokemon I select in my party. If celebi's trainer id is 31121 and secret id is 00000, how is it stored?

 

[esperance]

This article on Bulbapedia is actually a fairly complete explanation of the Pokémon data structure. The trainer/secret ID is stored as a 32-bit unsigned integer within the main Pokémon data structure. The upper 16 bits are the "secret ID" while the lower 16 bits are the "trainer ID" which you can see on the status screen.

 

[Touched]

You should use the pokemon_getattr/setattr functions already built into the game as the OTID (as mentioned on Bulbapedia) is part of the XOR encryption key and changing it will result in a bad egg.

To modify the TID with these functions you should use the attribute ID 1 (REQUEST_TID) which allow you to read and modify the original trainer ID without creating a bad egg (these functions handle encrypting and decrypting the Pokemon structure).

Example code

.thumb
.align 2

main:
push {lr}
@ place trainer ID on the stack to get a pointer to it
sub sp, #4
ldr r0, =(31121 | (00000 << 16))
str r0, [sp]
ldr r3, =0x0804037C|1 @ setattr
mov r2, sp @ pointer to ID
mov r1, #1 @ set trainer ID
ldr r0, =0x02024284 @ first pokemon in your party
bl call_via_r3 
add sp, #4
pop {pc}

call_via_r3: bx r3

 

[tkim]

You should use the pokemon_getattr/setattr functions already built into the game as the OTID (as mentioned on Bulbapedia) is part of the XOR encryption key and changing it will result in a bad egg.

To modify the TID with these functions you should use the attribute ID 1 (REQUEST_TID) which allow you to read and modify the original trainer ID without creating a bad egg (these functions handle encrypting and decrypting the Pokemon structure).

Example code

.thumb
.align 2

main:
push {lr}
@ place trainer ID on the stack to get a pointer to it
sub sp, #4
ldr r0, =(31121 | (00000 << 16))
str r0, [sp]
ldr r3, =0x0804037C|1 @ setattr
mov r2, sp @ pointer to ID
mov r1, #1 @ set trainer ID
ldr r0, =0x02024284 @ first pokemon in your party
bl call_via_r3 
add sp, #4
pop {pc}

call_via_r3: bx r3

I tried your example code but I got a bad egg. Don't I need to alter the checksum too? How would I recalculate the checksum?
edit: found pokemon_calc_checksum: .word 0x0803E3E8+1. I'll try modifying your example code by including this.
edit2: I have no idea how to include it... I tried adding

ldr r3, =0x0803E3E8|1
bl call_via_r3

do I also need .encrypt: .word 0x0803F8F9?

 

[Touched]

I tried your example code but I got a bad egg. Don't I need to alter the checksum too? How would I recalculate the checksum?
edit: found pokemon_calc_checksum: .word 0x0803E3E8+1. I'll try modifying your example code by including this.
edit2: I have no idea how to include it... I tried adding

ldr r3, =0x0803E3E8|1
bl call_via_r3

do I also need .encrypt: .word 0x0803F8F9?

The TID is not contained within the checksum, as the TID field itself is not encrypted. The checksum is made up of only the sum of the unencrypted half words in the encrypted block.

pokemon_setattr automatically calls pokemon_calc_checksum and pokemon_encrypt for the attributes that require it, and it also decrypts and re-encrypts the Pokemon, so if you're getting a bad egg then something else went wrong. Maybe try changing the "ldr r0, =(31121 | (00000 << 16))" line to something else?