Let me first ask when scanning DTC I might see P1103 008 vs P1103 035.
How do I follow the disassembly to determine how the 008 is set vs the 035?

And logic to set DTCs in general:

I can find WHERE (in which func) P1103 is set:

But I don't understand WHY it's set solely based on the disassembled code.

I get that the setDTC func uses the r12 and [r0+2]:



And that r12 is set right before calling the setDTC func, but the [r0xxx] statements confuse me. They're different before each setDTC func call:



And I get how to follow the decision tree to get to where [r0xxx] are set, but I can't match when/where/which [r0xxxx] is set to which [r0xxxx] is used for each setDTC func call. And what are the


calls doing exactly?






Where #45h Error Class is used, what do I look for to find what is being passed into the setDTC func as [r0+2] ?

snippet from first img:



Thanks in advance. I know I'm asking for a lot.

Rey

Follow the stack and look at the bitfield masks in hex

Thank you phila_dot. Reading that section now.

As for following the stack, easier said than done for those of us not having a background computer science

Ask any specific questions that you have, it's alot to try and do a whole writeup on your OP.

It's a top down stack.

[-r0] pushes onto the bottom (adds underneath)
[r0] accesses the current (bottom)
[r0+n] accesses n from the bottom
[r0+] pops off the bottom

It's a stack pointer, so [r0] is accessing the data stored and r0 is the stack pointer (memory address) itself.



As seen at the end of the function, this is resetting the stack pointer.

mov r4, #1h
mov [-r0], r4

Stack
1
----------------

mov r4, #2h
mov [-r0], r4

Stack
1
2
------------------

mov r4, #3h
mov [-r0], r4

Stack
1
2
3
-----------------

mov r4, [r0]

Stack
1
2
3

r4 == 3
-----------------

mov r4, #4h
mov [r0], r4

Stack
1
2
4
-------------------

mov r4, [r0+4]

Stack
1
2
4

r4 == 1
------------------

mov r4, #5h
mov [r0+4], r4

Stack
5
2
4
-------------------

mov r4, [r0+2]

Stack
5
2
4

r4 == 2
-----------------

mov r4, [r0+]

Stack
5
2

r4 == 4
----------------

add r0, #2h

stack
5

Edit: Corrected

i think phila_dot forgot about word and byte in his writeup

pointers