Learning ASM

[itsmeGames]

So me and AH are learning ASM now, and we've sort of figured some of it out, but there's problems when we tried to actually make a code.

So to start out, it's a really basic code. Slot cycler (U 1.0)

it should add 1 to whatever's in slot 1 (or so I thought)

ldr r0,=0x021D88FE
add r1,r0,#1
str r1,[r0]
bx  r14

and with comments (yay )

ldr r0,=0x021D88FE	; store slot one in r0
add r1,r0,#1		; r1 = r0 + 1
str r1,[r0]			; load r1 into r0
bx  r14				; end the branch

and so the ARDS comes out as

023FF090 012FFF11
E0000000 00000014
E59F0008 E2801001
E5801000 E12FFF1E
021D88FE 00000000
023FF090 E3520003

I put an R activator on it

so anyway, it work sort of... except it doesn't add 1 to the item...
I typed in 0019 in text to item to get a blue rose seed, then I checked (the blue rose seed was there)
then I tapped R and...
*poof* my blue rose seed had changed into an item with no name

I also tried making FFF0 into FFF1... but it just changed it into who knows what

EDIT: I also tried this one now:

ldr r0,=0x021D88FE
ldr r1,[r0]
add r1,#1
str r1,[r0]
bx  r14

getting this:

94000130 FEFF0000
023FF090 012FFF11
E0000000 00000018
E59F000C E5901000
E2811001 E5801000
E12FFF1E 021D88FE
023FF090 E3520003
D2000000 00000000

and it gave me the same results... :/


I'm about to try this one:

ldr r0,=0x021D88FE
ldr r0,[r0]
add r1,r0,#0x1
str r1,[r0]
bx  r14

94000130 FEFF0000
023FF090 012FFF11
E0000000 00000018
E59F000C E5900000
E2801001 E5801000
E12FFF1E 021D88FE
023FF090 E3520003
D2000000 00000000

does that seem more right?

EDIT 2: that didn't work either, that just made no modifying to it at all

[Maniac]

ldr r0, Slot
ldrh r2,[r0]
add r1,r0,#0x1
strh r1,[r0]
bx  lr

Slot:
.long 0x021D88FE

Or how you had it...

ldr r0, =0x021D88FE
ldrh r2,[r0]
add r1,r0,#0x1
strh r1,[r0]
bx  r14

It does the same thing, the other way is just for organization and how I'm use to seeing things.

Try that. :P If it doesn't work I'll have to put another register in.

[itsmeGames]

ah! thank you! I didn't think to use half words! (ok, I did for a sec but didn't know the command :P)

but! it still didn't work :P

I'm trying this one now:

ldr r0,=0x021D88FE
ldrh r2,[r0]
add r1,r2,#0x1
strh r1,[r0]
bx  r14

but it didn't work either

[Area51_Hacker2]

i take it lrdh is load half word

But it still doesn't explain why its adding so much :S

[Vash]

Hm, have you watched the value change when you're using the code? Try an activator. When I use ldrh for a half word, it's putting the bytes in reverse order. Make sure the bytes are in the correct order when you're using ldrh.

[itsmeGames]

ldr r0,=0x021D88FE
ldrh r2,[r0]
add r2,#0x1
strh r2,[r0]
bx  r14

Doesn't add automatically add one to the last byte?

*joes to test it with furniture*

Ah ha! I found the problem (I hope) but it's a different problem
For some reason, it seems to loop even though I have a terminator!

I put in 3000, and I tested this code a few times. My results were that it added:
0xCC-0xCF
0x74-0x77
0x2C-0x2F

each time I tapped L and R quicker than the time before...
so that means the code does work, but it loops for some reason >_>

The code I am using for it is:

94000130 FCFF0000
023FF090 012FFF11
E0000000 00000018
E59F000C E1D020B0
E2822001 E1C020B0
E12FFF1E 021D88FE
023FF090 E3520003
D2000000 00000000

shouldn't that not loops because of the terminator though?

[Vash]

add = register + #immediate.

I'm definitely not the person to be asking but as I understand it, yours adds #0x1 to the address. ex. 0x02000000 goes to 0x02000001. I could be wrong.

Here's an example from one of my ASM codes I'm working on:

ldr r0, =0x021ECB88
add r0,#1
strb r2, [r0]

That takes the address, changes it to 0x021ECB89 then stores one byte from r2 to that address.

[itsmeGames]

I don't wanna change the address, I wanna change what's in it, and it actually is doing that :P

here's what mine does:

ldr r0,=0x021D88FE <- takes the address
ldrh r2,[r0] <- takes what's stored in the address
add r2,#0x1 <- adds one to what's stored in the address
strh r2,[r0] <- stores it back in the address
bx r14


maybe it's a problem with the activator?

[Vash]

Haha, see? I was wrong

Anywho, I'd wait for Maniac or Toe to check out your problem. Seems like it should work to me...

[itsmeGames]

pretty much, it works right in adding one to whatever's in slot one, but it keeps doing it over and over the longer you're holding down the activator :/

how do we fix that?

Hm, have you watched the value change when you're using the code? Try an activator. When I use ldrh for a half word, it's putting the bytes in reverse order. Make sure the bytes are in the correct order when you're using ldrh.

that's because of how it stores words and halfwords and bytes, it's backward :P
bx = byte number

4 bytes:
0xb1 0xb2 0xb3 0xb4

2 halfwords:
0xb2b1 0xb4b3

1 word:
0xb4b3b2b1


(sorry if I showed that wrong, I can't quite remember but that looks right >_> )

but assuming that's right, pretend you say Hello me
space will be represented by _ and every two letters will be a byte
you get it this way in bytes:
H e l l o _ m e
this way in halfwords:
eH ll _o em
and this way as words:
lleH em_o
assuming you wanna go up to dwords, you get:
em_olleH

the phrase in reverse