Program Counter Relative Addressing?

[ceharris]

I'm trying to use program counter relative addressing and getting an unexpected assembler error.

hello.asm:

        org $ff00

        ; this instruction should produce 30 8D 00 00
        ; but instead causes an error
        leax message,pcr

message:
        fcc 'Hello, world.'
        fcb $0d
        fcb $0a
        fcb 0

$ 6809 -r -d -b hello.asm
INFO: Assembling hello.asm
Pre-processing...
line 6 register missing after offset
Error: cpu::Error: line 6 register missing after offset

[gorsat]

Great catch! Thanks for finding this. I hadn't implemented PC-based indexing at all in the assembler. Strange that I never ran into it after all the code I assembled. I think I've adopted the standard syntax for this but please let me know if not.

; for PC-relative addressing
   LEAX target,PCR
; for regular old indexed addressing using the program counter
   LDX offset,PC

...and it turns out I also had a bug in the emulator side as well where I wasn't properly adding the instruction size to the offset in the case of a 16-bit PCR offset.

One thing to note, though. You said you expected leax message,pcr to become 30 8d 00 00 but my code outputs 30 8c 00 because the offset fits into 8 bits.

You can try test/issue1.asm to see what it's doing:
cargo run -- -v -l -r --acia-disable test/issue1.asm

I see there are a ton of warnings now using the latest toolchain so I'll clean it up tomorrow.

[ceharris]

One thing to note, though. You said you expected leax message,pcr to become 30 8d 00 00 but my code outputs 30 8c 00 because the offset fits into 8 bits.

Of course -- makes sense.

Thanks for the quick turnaround! I'll give it whirl later today...

And thanks for putting this emulator together. Super helpful to have an emulator for testing and debugging before writing to EEPROM for my 6809-based retro-computing project. 😄

[ceharris]

Just to follow-up... PCR is working now as expected.