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subroutine, and how it is used with the call and return instructions.

subroutine, and how it is used with the call and return instructions.

Computer Networking: A Top-Down Approach (7th Edition)
Computer Networking: A Top-Down Approach (7th Edition)
7th Edition
ISBN:9780133594140
Author:James Kurose, Keith Ross
Publisher:James Kurose, Keith Ross
Chapter1: Computer Networks And The Internet
Section: Chapter Questions
Problem R1RQ: What is the difference between a host and an end system? List several different types of end...
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(a) Describe the term subroutine, and how it is used with the call and return instructions.

(b) Explain the term stack overflow and how it will happen in the PIC16F84A.

 

(c) Consider the following program in Figure 2, replacing the call shuffle up instruction with goto
shuffle up, leaving all else unchanged. Build, simulate and step through the program. Explain the
effect of replacing call with goto?

**... :Fibonacci_SRS ;This program rewrites the Full Fibonacci progran to illustrate the use of subroutines. ;Program intended for sinulation only, hence no input/output. TJW 17.11.08 Tested by simulation 17.11.08 (initial program sections omitted) forward movf fibl,0 addwf fib2,0 btfsc status,c :test if we have overflowed 8-bit range goto reverse ihere if we have overflowed, ;hence reverse down the series movwf fibtemp incf counter,1 ;latest number now placed in fibtemp now shuffle numbers held, discarding the oldest call shuffle_up goto forward z when reversing down, we will subtract fibo from fibl to form new fibo reverse movf fib0,0 subwf fibl,0 movw! fibtemp decf counter, 1 ;now shuffle numbers held, discarding the oldest call shuffle_down ;latest number now placed in fibtemp ;test if counter has reached 3, in which case return to forward movf counter,0 sublw 3 btfac status,z goto goto forward reverse ...... ..... :Subroutines ;Shuffles numbers in series, moving fibl to fibo, fib2 to fibl, fibtemp to fib2 shuffle_up movf fibl,0 ifirst move middle number, to overwrite oldest movwf fib0 movf fib2,0 movwf fibl movf fibtemp,0 movwt fib2 return :Shuffles numbers in series, moving fibl to fib2, fibo to fibl, fibtemp to fibo ;first move middle number, to overwrite oldest shuffle_down movf fibl,0 movwf fib2 movf fibo,0 movwf fibl movf fibtemp,0 movwf fibo return end Figure 2: Using subroutines in the Fibonacci program
Transcribed Image Text:**... :Fibonacci_SRS ;This program rewrites the Full Fibonacci progran to illustrate the use of subroutines. ;Program intended for sinulation only, hence no input/output. TJW 17.11.08 Tested by simulation 17.11.08 (initial program sections omitted) forward movf fibl,0 addwf fib2,0 btfsc status,c :test if we have overflowed 8-bit range goto reverse ihere if we have overflowed, ;hence reverse down the series movwf fibtemp incf counter,1 ;latest number now placed in fibtemp now shuffle numbers held, discarding the oldest call shuffle_up goto forward z when reversing down, we will subtract fibo from fibl to form new fibo reverse movf fib0,0 subwf fibl,0 movw! fibtemp decf counter, 1 ;now shuffle numbers held, discarding the oldest call shuffle_down ;latest number now placed in fibtemp ;test if counter has reached 3, in which case return to forward movf counter,0 sublw 3 btfac status,z goto goto forward reverse ...... ..... :Subroutines ;Shuffles numbers in series, moving fibl to fibo, fib2 to fibl, fibtemp to fib2 shuffle_up movf fibl,0 ifirst move middle number, to overwrite oldest movwf fib0 movf fib2,0 movwf fibl movf fibtemp,0 movwt fib2 return :Shuffles numbers in series, moving fibl to fib2, fibo to fibl, fibtemp to fibo ;first move middle number, to overwrite oldest shuffle_down movf fibl,0 movwf fib2 movf fibo,0 movwf fibl movf fibtemp,0 movwf fibo return end Figure 2: Using subroutines in the Fibonacci program
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