Process of assembly instruction execution

;#****************************************************************************************** ; # NAME:ARM_CODE2.S *; # author:wuhan center,embest *; # Desc:arm InStr uction examples *; # Example for Condition Code *; # HISTORY:SHW. He 2005.02.22 *; #****************************************************************************************								 				    ;/*------------------------------------------------------------------------------------------* *;/* Code *//*------------------------------------------------------------------------------------------*/IS A start,code,readwrite entry code32 num equ 2;/* Number of entries in jump table */export Reset_handler R Eset_handler mov r0, #0;/* Set up the three parameters */mov r1, #3 mov r2, #2 bl arithfunc;/* C All the function */

;/* dead loop */stop B stop; # ************************************************************************ ; # * According R0 Valude to execute the code *; # ************************************** Arithfunc;/* Label the function */CMP r0, #num; * Treat function code as unsigned integer */BHS Doadd;/* If code is >=2 then do operation 0. */ADR R3, jumptable;/* Load Address of Jump table */Ldr PC, [r3,r0,lsl#2];/* Jump to the appropriate Rou Tine */

                                                                         ;/*pc = r3 + r0<<2*/
jumptable
		DCD		doadd                                ; it occupies 4 bytes, which stores the doadd corresponding to the address
		DCD		dosub                                ; It occupies 4 bytes, which stores the corresponding address of dosub

doadd
		add		r0, R1, R2;/					*  operation 0, >1 */
		BX		LR 							;/*  return */


dosub
		Sub		r0, R1, R2					;/*  Operation 1 */
		BX		lr;/							*  return */

		end									;/* Mark the end of this  file */

Before you perform BL Arithfunc

After execution:

It stores the value of the PC in R14 (LR).

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