[ASM & Hex] Trouble with an ASM routine

JapaBijou · Nov 27, 2020

Hi guys

I've started to study asm, so I decided to try to create some routines as training, but I bumped into a problem:

The purpose of this routine is to heal every pokémon that is not fainted (so their hp must be different from 0, useful for things such as nuzlocke challenge ROM).
The routine iterates every pokémon in the party, until it finds a pokemon with level equal to 0 (because that's impossible so the party is over) and then quit

The Flow-Chart is the following:

Spoiler:

The code is the following:

Spoiler:

Code explanation:

Spoiler:

I execute the routine in Littleroot town sign placed at position (000F;000D):

Spoiler:

I know that that routine is not the best way to handle only-one-dead-rule in a nuzlocke rom (because I should remove all healing items, change all pkmn center script and then it wouldn't work anyway because of healing-box), but this is only an exercise.

I'm not 100% sure,but the offset should be right.

So I have some questions:

1) Why does the game restart when I talk to the sign?
2) Can I use thumb set instead of arm set? The compiler told me that "Thumb does not support conditional execution", but I saw that on this forum someone using conditional branches with thumb.

Thanks for all

-JapaBijou

Anon822 · Nov 27, 2020

If you just want to just hack the gen3 games, you might find using the decompilations easier than assembly.
For example, in pokeemerald you could do this simply with:

Code:

int i;
for(i = 0; i < gPlayerPartyCount; i++){
	if(gPlayerParty[i].hp != 0) gPlayerParty[i].hp = gPlayerParty[i].maxHP;
}

But to actually answer your questions:
1) The game crashes because the processor is still in ARM-mode when you return to the game's thumb code by popping pc.
You should either just use thumb code or to return with the bx instruction, which can change the processor mode.

2) You're trying to use branch-with-link (BL) with conditions, which is not allowed in thumb mode, instead you should be using the branch instruction (B).
also you're using ldrb for loading single-byte constants like total_HP_offset, which is also not allowed, use mov instead.

JapaBijou · Nov 27, 2020

If you just want to just hack the gen3 games, you might find using the decompilations easier than assembly.
For example, in pokeemerald you could do this simply with:

int i;
for(i = 0; i < gPlayerPartyCount; i++){
if(gPlayerParty.hp != 0) gPlayerParty.hp = gPlayerParty.maxHP;
}

Click to expand...

How can I do that?

But to actually answer your questions:
1) The game crashes because the processor is still in ARM-mode when you return to the game's thumb code by popping pc.
You should either just use thumb code or to return with the bx instruction, which can change the processor mode.

2) You're trying to use branch-with-link (BL) with conditions, which is not allowed in thumb mode, instead you should be using the branch instruction (B).
also you're using ldrb for loading single-byte constants like total_HP_offset, which is also not allowed, use mov instead.

Click to expand...

I managed to switch to thumb using b instead of bl. What is the difference between those two?
Anyway, I changed the code:

Spoiler:

.thumb
.align 2

main:
/*
r0 -> address
r1 -> offset to add to r0
r2 -> data taken from r0 address
*/

push {r0-r2,lr}

ldr r0,pokemon_memory_start

loop:
mov r1,#level_offset
add r0,r1
ldr r2,[r0]

cmp r2,#0
bNE finish

sub r0,r1

mov r1,#current_HP_offset
add r0,r1
ldr r2,[r0]
sub r0,r1

cmp r2,#0
bNE restore_pokemon
add r0,#0x64
b loop

restore_pokemon:
mov r1,#total_HP_offset
add r0,r1
ldrh r2,[r0]
sub r0,r1
mov r1,#current_HP_offset
add r0,r1
strh r2,[r0]
sub r0,r1
add r0,#0x64

b loop

finish:
pop {r0-r2,pc}

.align 2

pokemon_memory_start:
.word 0x020244EC

level_offset:
.byte 0x54

current_HP_offset:
.byte 0x56

total_HP_offset:
.byte 0x58

But compiler give me this error:

D:\..\temp.asm: 16: Error: cannot represent THUMB_IMM relocation in this object file format
D:\..\temp.asm: 25: Error: cannot represent THUMB_IMM relocation in this object file format
D:\..\temp.asm: 36: Error: cannot represent THUMB_IMM relocation in this object file format
D:\..\temp.asm: 40: Error: cannot represent THUMB_IMM relocation in this object file format

What that mean?

Thanks again

EDIT:

I removed r1 and add offsets in this way:

Spoiler:

.thumb
.align 2

main:
/*
r0 -> address
r1 -> offset to add to r0
r2 -> data taken from r0 address
*/

push {r0,r2,lr}

ldr r0,pokemon_memory_start

loop:
add r0,#0x54
ldr r2,[r0]

cmp r2,#0
bNE finish

sub r0,#0x54

add r0,#0x54
ldr r2,[r0]
sub r0,#0x54

cmp r2,#0
bNE restore_pokemon
add r0,#0x64
b loop

restore_pokemon:
add r0,#0x58
ldrh r2,[r0]
sub r0,#0x58
add r0,r1
strh r2,[r0]
sub r0,#0x56
add r0,#0x64

b loop

finish:
pop {r0,r2,pc}

.align 2

pokemon_memory_start:
.word 0x020244EC

Now it compiles and game doesn't reset but doesn't heal my team.
Why?

Anon822 · Nov 27, 2020

You can find a tutorial for setting up pokeemerald here: https://www.pokecommunity.com/showthread.php?t=426921

Your team doesn't get healed because your code is buggy:
- it jumps to finish when level is not 0
- it's reading the level a second time instead of hp
- It's accessing level as 4 bytes instead of 1
- it's using r1 even though you haven't set its value
...and maybe more.

JapaBijou · Nov 27, 2020

Oh it worked!

I should work slower in order to avoid those careless mistakes

Thanks for all

[ASM & Hex] Trouble with an ASM routine

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