Start on the Program

The flowchart for the program is at right. The first box sets a flag to a default value in advance of the test that might change it. This is a common trick. Here is an outline of the program:

## tempRange.asm
##
## Check that   30 <= temp <= 55
## Set flag to 1 if in range, to 0 if out of range
##
## Registers:
## $2 -- temperature
## $3 -- in range / out of range indicator flag
## $8 -- scratch

      .text
      .globl  main
# Set range indicator to 1
main:   ori     $3,$0,1         #  set to 1

# Test  30 <= temp <= 55
        sltiu   $8,$2,     #  $8=1 if temp <= 55
        
        beq     $8,$ ,   #  0? out of range
        
        sll     $0,$0,0         #  delay

       . . . .                  #  more instructions

# Out of Range: clear range indicator to 0
out:
       . . . .                  #  clear flag to 0

# continue
cont:  sll     $0,$0,0         #  target for the jump

The range test is in two parts. The first part (in this program) tests if temp is less than or equal to 55. However, the machine instruction is "set on less than". If temp is out of range a branch is taken to out. The branch is followed by a no-op for the branch delay.