post increment addressing mode works correctly?
Closed this issue · 6 comments
Does post increment addressing mode works properly?
When traced execution of a program
LEA $1200,A0
MOVEQ #$55,D2
EOR.B D2,(A0)+
and changed memory view to address $1200, noticed that the last instruction worked as "pre increment", not "post increment", because of changing value under $1201, not $1200 address.
Ah yes i just noticed this, i tried to test it on Easy68K and it wrote to 1200 as expected
I found the affected code
increment of post increment: here
eor instruction: here
The issue being that the register is read (and incremented) and then written (not incremented) while it should be the opposite
It should be easy to fix, i need to add a new parameter to the get_operand_value that counts how many times the parameter is used, if it's a pre increment, then the get should increase it regardless, but if it's a post, it increases it only if Used::once. in the store it's the opposite, if it's post pre increment, then update only if Used::once, if post increment, update regardless
i'm a bit busy lately so might take a bit to fix the bug, thanks for letting me know though!
I hope this helps. Sometimes it's more convenient to use your online assembler/debugger than Easy68K or any other installed.
Yup i'm doing the fix now! it was way easier than i expected, i should be finished in a few hours.
Just for curiosity, why are you writing m68k? is it for some sort of lectures or just for fun?
Seems to be working! I just published the changes
also thanks to @transistorfet the inspriation of the Used::Twice/Used::Once
Yup i'm doing the fix now! it was way easier than i expected, i should be finished in a few hours.
Just for curiosity, why are you writing m68k? is it for some sort of lectures or just for fun?
Years ago I did a lot of coding in 68K, now I use it to teach students processor programming.
Checked, now works properly:) Thanx a lot!
Years ago I did a lot of coding in 68K, now I use it to teach students processor programming
That's the whole reason why i made the interpreter, the learning curve for assembly is so steep at the beginning because of the lack of "easy to use" tools to teach the basics, i'm glad it's been useful.
Thanks again for the bug report! It also made me spot a similar bug which i fixed