JSRR won't go to outside program in LC3

Question

I seem to be having a problem with LC3 assembly.

I'm trying to jump to a subroutine (in another program, otherwise I'd just use JSR), but instead it just goes through to the next command.

I've tried:

    LD R0, Subpgm
    JSRR R0

and at the bottom, This line to define Subpgm.

    Subpgm .FILL x4000

I expected this to jump to PC x4000, but instead the PC is just incremented by the normal 1.

Any help would be super appreciated!

Answer 1

Here's an example program using the JSRR instruction.

       .ORIG X3000
       LD R0, Subpgm  ; => R0=X4000
       JSRR R0        ; => R7=X3002 PC=X4000
Done   HALT           ; This is at X3002
Subpgm .FILL X4000    ; Address of the 'external' program
       .BLKW X0FFC    ; Fill up the gap between programs
       RET            ; This is at X4000
       .END