Write assembly language code for all type of the conditional and unconditional program flow control instructions.

;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 embedded C and assembly code to understand program flow instructions for "for loop".

Usually, we start coding with assembly and than we move to the embedded C code. In this case we first understand the  embedded C code and than we will write the equivalent assembly code to mimic the same thing.

Embedded C code:

int main ()
{
volatile unsigned int total, i;

total = 0;                    // initialize the total
        for (i=0;i<5;i=i+1)
        {
        total = total + i;
        }
return(0);
    
}

       
 Result:

 

Assembly language code:

        TTL transfer
        AREA Myprog, CODE, READONLY
ENTRY
        EXPORT main
main
        MOVS R2, #0 ; Total = 0
        MOVS R1, #0 ; i = 0
loop
        ADDS R2, R2, R1 ; Total = Total + i
        ADDS R1, R1, #1 ; i = i + 1
        CMP R1, #5 ; compare i to 5
        BLT loop ; if less than then branch to loop
done
        SWI &11
        END

Result: