;Write assembly language code for all type of the conditional and
;unconditional program flow control instructions.
; 1- unconditional jump
; 2- conditional jump
; 2.1 - signed and unsigned conditional jump based on comperision
; 2.2 - signed and unsigned conditional jump based on overflow
; 2.3 - signed conditional jump based on N flag
TTL transfer
AREA Myprog, CODE, READONLY
ENTRY
EXPORT main
main
;************************unconditional branch*****************************************
;Table 1: branch instructions with ranges
;==============================================================================
;Branch range Available instruction
;==============================================================================
;Under +/–254 bytes B label
; B<cond> label
;Under +/–2 KB B label
;Under +/–16 MB BL label
;Over +/–16 MB LDR R0, =label ; Load the address value of label in R0
; BX R0; Branch to address pointed to by R0, or
; BLX R0; Branch to address pointed to by R0 and update LR
;==============================================================================
B LOAD_R2 ; B to the label
load_return
;Branch and link with updated value of LR = R14
BL LOAD_ADD1 ;branch and updated PC link to the LR(R14), return to the next instruction
; address of MOVS R1,#3 will store into the LR for return
MOVS R1,#3
MOVS R2,#3
MOVS R3,#4
;*****************************conditional instructions***************************
;Table2: Conditional branch instructions for value comparison operations
;=============================================================================
;Required branch control Unsigned data Signed data
;=============================================================================
;If (R0 equal R1) then branch BEQ label BEQ label
;If (R0 not equal R1) then branch BNE label BNE label
;If (R0 > R1) then branch BHI label BGT label
;If (R0 >= R1) then branch BCS label/BHS label BGE label
;If (R0 < R1) then branch BCC label/BLO label BLT label
;If (R0 <= R1) then branch BLS label BLE label
;=============================================================================
;for signed and unsigned equ and Not equ
CMP R2, R1 ; compare the R2 with R1 and reflect the status in FLAGS
BEQ LOOP3 ;branch if R2 = R1
LOOP3 CMP R2,R3 ; compare the R2 with R3 and reflect the status in FLAGS
BNE LOOP4_1 ; branch if R2 != R3
;unsigned greater than/equal and less than/equal
LOOP4_1 MOVS R1,#5 ;Loop counter starting value is 5
LOOP4
ADDS R4, #1
CMP R1, R4
BLO LOOP5 ;branch if R1<R4/ R1 is lower than R4
SUBS R1, #1
BHI LOOP4 ;branch if R1 is higher than 1
LOOP5 MOVS R1,#6 ;Loop counter starting value is 6
ADDS R4, #1
CMP R1, R4
BLS LOOP6 ;branch if R1<= R4/ R1 lower than or same to R4
SUBS R1, #1
BHS LOOP5 ;branch if R1 is higher and same to 1
;signed greater than/equal and less than/equal
LOOP6 MOVS R1,#5 ;Loop counter starting value is 5
MOVS R4,#0 ;Set R4 to zero
LOOP7
ADDS R4, #1
CMP R1, R4
BLT LOOP8 ;branch if R1<R4
SUBS R1, #1
BGT LOOP7 ;branch if R1>1
LOOP8 MOVS R1,#6 ;Loop counter starting value is 3
ADDS R4, #1
CMP R1, R4
BLE LOOP9 ; branch if R1<=R4
SUBS R1, #1
BGE LOOP8 ; branch if R1>=1
;Table3: Conditional branch instructions for overflow detections
;==============================================================================
;Required branch control Unsigned data Signed data
;==============================================================================
;If (overflow(R0 + R1)) then branch BCS label BVS label
;If (no_overflow(R0 + R1)) then branch BCC label BVC label
;If (overflow(R0 – R1)) then branch BCC label BVS label
;If (no_overflow(R0 – R1)) then branch BCS label BVC label
;==============================================================================
;Table4: Conditional branch instructions for positive or negative value detection
;==============================================================================
;Required branch control Unsigned data Signed data
;==============================================================================
;If (result >=0) then branch Not applicable BPL label
;If (result < 0) then branch Not applicable BMI label
;==============================================================================
;unsigned overflow detection/ carry flag based branch
LOOP9
LDR R6,=0xFFFFFFFF
LDR R5,=0x00000001
LOOP11 ADDS R6,R6,R5
; during first addition carry flag is set, ans is C=1 R6=0x00000000
; during second addition carry flag is reset, ans is C=0 R6=0x00000001
BCC LOOP10 ;branch if C=0
BCS LOOP11 ;branch if C=1
;above example peform the overflow for addition operations
;for subtraction you can do it by your own
;Signed overflow incorporate signed ov, carry and Signed flag
LOOP10
LDR R6,=0xFFFFFFFF
LDR R5,=0x80000000
LOOP12 ADDS R6,R6,R5
; during first addition sign change and ov flag is set, ans is N=0,C=1,ov=1 R6=0x7FFFFFFF
; during second addition sign changes and ov flag is reset, ans is N=1,C=0,ov=0 R6=0xFFFFFFFF
BVC LOOP13 ;branch if V=0
BCS LOOP15 ;branch if C=1
LOOP15 BPL LOOP16 ;branch if N=0
LOOP16 BVS LOOP12 ;branch if V=1
LOOP13 BCC LOOP14 ;branch if C=0
LOOP14 BMI LOOP17 ;branch if N=1
LOOP17 B done
LOAD_R2
MOVS R2,#0X04
LDR R0,=load_return ; psudo load value of label into the R0 for BX instruction
BX R0 ; unconditional return through branch and exchange
;loop inside the loop
;use of BLX and BL with <Rm>
LOAD_ADD1
MOV R1,R14 ;Storing the LR(R14) value into R1 for further use
LDR R2,=load
BLX R2 ;Jump to the PC where R2 is pointing and update LR with new value
LDR R3,=add2
BLX R3 ;Jump to the PC where R3 is pointing and update LR with new value
BX R1 ;Return from original location/ return to the line BL LOAD_ADD1
;load subroutine
load LDR R6,=0x034
LDR R7,=0x235
BX LR ; return to the line next to BLX R2
;add subroutine
add2 ADDS R6, R7, R6
BX LR ; return to the line next to BLX R3
done
SWI &11
END
Write assembly language code for all type of the conditional and unconditional program flow control instructions.
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