Immediate data Immediate operands : ADD r3, r3, #1 valid ADD r3, #1,#2 invalid ADD #3, r1,r2 invalid ADD r3, r2, #&FF ( to represent hexadecimal immediate , use &) Ox1234 uses 16 bits For binary number: suffix the number with 0b For octal number: suffix the number with 0 For hexadecimal numbers: suffix the number with 0x, 0X or &

Barrel Shifter Barrel Shifter is a functional unit which can be used in a number of different circumstances. It provides five types of shifts and rotates which can be applied to Operand2.

Barrel Shifter ASL: Arithmetic Shift left, this is synonym for LSL

Barrel Shifter

Examples of Barrel Shifter MOV r0, r0, LSL #1 ; r0 = r0 * 21 MOV r1, r1, LSR #2 ; r1 = divide r1 by 4 (unsigned) MOV r2, r2, ASR #2 ; r2 = divide r2 by 4 (signed) MOV r3, r3, ROR#16 ; swap the top and bottom halves of r3 ADD r5, r5, r3, LSL #4 ; 4-address instruction ;r5 = r5+ r3 * 24

Operand 2

I bit in the instruction

If I bit is 0, operand 2 is Register Registers shifted by values: MOV r2, r2, LSR #1 ;shift r2 right by one bit RSB r10 r5, r11, ASR #14 ;shift r11 right by14 bits while sign extending, then subtract r5 from that. Put the result in r10. Registers shifted by registers: BIC r11, r11, r1, LSL r0 ;take r1 and shift it left by r0, then use that as a mask to clear bits in r11. Put the result in r11 CMP r9, r8, ROR r0 ;take r8 and rotate it right by r0, then compare that with r9. the result is in flags

If I bit is 0, operand 2 is in register

If I bit is 1 – Immediate operand

Instruction format

What is the maximum value that can be represented by immediate operands? 12 bits -----> 2^12 -- 0 to 4095 (in other processors 16 bits for immediate operands, so 2^16) But using 8 bits and shift operations(4 bits) can represent a 32 bit data

What are the different ways to represent operands ? In Register, Immediate , barrel shifter …

Condition code

Eg - to set condition bits Setting condition bits § Simply add an ‘S’ following the arithmetic/ logic instruction § Example: ADDS r0,r1,r2 (in ARM) This is equivalent to r0=r1+r2 and set the condition bits for this operation

Data Processing Instructions (3) Conditional codes + Data processing instructions Barrel shifter = Powerful tools for efficient coded programs

Data Processing Instructions (4) e.g.: if (z==1) R1=R2+(R3*4) compiles to CMP ADDEQS R1,R2,R3, LSL #2 ( SINGLE INSTRUCTION ! )

C

Instruction format