Starter code for PS7 queue size.

queue_size_starter.asm

;
; queue_size.asm - subroutine to check queue size.
;

.ORIG x3000

        LD R3, FIRST    ; initialize front/head
        ADD R3, R3, #1  ; add offset to test different values
        LD R4, FIRST    ; initialize rear/tail
        ADD R4, R4, #3  ; add offset to test different values

        JSR Q_SIZE      ; call subroutine
        HALT            ; put breakpoint here to check value in R5

; ---------------------- QUEUE SIZE SUBROUTINE ---------------------- ;
; Description: computes current size of the queue
; Inputs: R3 - front/head, R4 is rear/tail
; Outputs: R5 - size
; NOTE: update FIRST/LAST based on start point and end point of queue

Q_SIZE
        RET

Q_R1    .BLKW 1
Q_R2    .BLKW 1

FIRST   .FILL x4000     ; starting address of queue storage
NEG_1ST .FILL xC000     ; negative of FIRST
LAST    .FILL x4005     ; ending address of queue storage
NEG_LST .FILL xBFFB     ; negative of LAST

.END