Instruction System Procedure & System Routine 计算机学院 李征 Tel：13882153765 Email：email@example.com OICQ: 1340915 Procedure & System Routine Procedure: A software module which is with independent function and can be used repeatedly. The usage of procedure must include calling and returning operation. System Routine: A procedure which perform some system functions and can be triggered by an interrupt request. Procedure Calling Direct Calling: CALL PROC_NAME Near Direct Calling: If PROC_NAME is in the same segment with ‘CALL’. SP <= (SP)-2 (SP) <= (IP) IP <= Offset of PROC_NAME Procedure Calling Far Direct Calling: If PROC_NAME is not in the same segment with ‘CALL’. SP <= (SP)-2 (SP) <= (CS) SP <= (SP)-2 (SP) <= (IP) CS <= Segment of PROC_NAME IP <= Offset of PROC_NAME Procedure Calling Indirect Calling Near Indirect Calling: CALL register or memory cell Example: CALL BX CALL [BX] Procedure Calling Far Indirect Calling: CALL DWORD PTR memory cell Example: CALL DWORD PTR [BX+100H] Procedure Returning Near Returning: RETN IP <= ((SP)) SP <= (SP)+2 Procedure Returning Far Returning: RETF IP <= ((SP)) SP <= (SP)+2 CS <= ((SP)) SP <= (SP)+2 Procedure Returning PROC_NAME PROC (FAR or NEAR) …… RET ; If this is a near procedure, ‘RET’ will be ; assembled to ‘RETN’. Or else, it will be ; assembled to ‘RETF’. PROC_NAME ENDP Procedure Returning Returning with parameter clearing: RET N; N must be an even integer. IP <= ((SP)) SP <= (SP)+2 CS <= ((SP)) ; if far SP <= (SP)+2 ; if far SP <= (SP)+N This instruction clears N / 2 parameters which is in stack and transferred from calling program. Stack Operation in Near Calling and Returning Example: Assume A is calling program, B, C, and D are near procedures. When executing, A calls B, B calls C, and C calls D. Stack Operation in Near Calling and Returning C的返回点 B的返回点 SP A的返回点 Notes for Procedure Design Notes for Procedure Design: 1) ‘CALL’ and ‘RET’ instructions must match. 2) CPU execution scene must be preserved in procedure. 3) Parameter transfer agreement must be kept by both calling program and procedure. Parameter transfer in Procedure Three parameter transfer methods: 1) Transfer with Register 2) Transfer with Stack 3) Transfer with Parameter Region in Data Segment Parameter transfer in Procedure Example of parameter transfer with stack: Procedure Function: Transfer a given 8-bit or 16-bit binary to an ASCII string composed of ‘1’ and ‘0’. Preserve the string at given position in memory. Parameter transfer in Procedure Input Parameter: 1) Binary given by calling program 2) Bit number of binary given by calling program 3) Memory address given by calling program for string storage Output Parameter: None Parameter transfer in Procedure C function: void Transfer_Bin（BYTE* lp_Data, int Bit_Num, char* lp_Res） Parameter transfer in Procedure DATA SEGMENT BIN8 DB 57H BIN16 DB 47bcH ASCBUF DB 20H DUP(20H) DATA ENDS STACK1 STACK1 SEGMENT STACK DW 40H DUP(0) ENDS Parameter transfer in Procedure CODE SEGMENT ASSUME CS:CODE,DS:DATA,SS:STACK1 MAIN: MOV AX, DATA MOV DS, AX ;Transfer Given 8-bit Binary MOV AX, 0 MOV AL, BIN8 PUSH AX ; Transfer Bit Number MOV AX, 8 PUSH AX Parameter transfer in Procedure ; Transfer given string address LEA AX, ASCBUF PUSH AX CALL BITASC ; call procedure ; The second calling MOV AX, BIN16 PUSH AX MOV AX, 16 PUSH AX Parameter transfer in Procedure LEA PUSH CALL MOV INT AX, ASCBUF+10H AX BITASC AH, 4CH 21H Parameter transfer in Procedure ;Procedure BITASC PROC ; Use BP to extract parameter, ; not SP MOV BP, SP ; Preserve CPU execution scene PUSH AX PUSH CX PUSH DX PUSH DI Parameter transfer in Procedure MOV MOV MOV CMP JNE MOV DI, [BP+2] CX, [BP+4] DX, [BP+6] CX, 8 TRANS DH, DL Parameter transfer in Procedure TRANS: ROL DX, 1 ; Transform each bit MOV AL, DL AND AL,1 ADD AL, 30H MOV [DI], AL INC DI LOOP TRANS ; Restore CPU execution scene POP DI POP DX Parameter transfer in Procedure BITASC CODE POP CX POP AX ; Return and clear parameters RET 6 ENDP ENDS END MAIN Parameter transfer in Procedure If there are output parameters, they can be put to stack by procedure. Generally, output parameters replace input parameters in stack. After returning, calling program extract output parameters from stack top. System Routine Most system routines are used for I/O interaction between CPU and interface or some system operations. System routines can be triggered by interrupt request, and can be called by program. System Routine If system routine is called in program, ‘INT’ instruction is used. INT N N is the routine number, not the procedure name (beginning address). System Routine Execution of ‘INT’: 1) SP <= (SP)-2 2) (SP) <= (FR) 3) SP <= (SP)-2 4) (SP) <= (CS) 5) SP <= (SP)-2 6) (SP) <= (IP) 7) IF <=0, TF <=0 8) Transform N to beginning address of routine 9) CS <= Segment of beginning address 10) IP <= Offset of beginning address System Routine Routine1 PROC …… IRET Routine1 ENDP ‘IRET’ used in system routine, rather than ‘RET’. System Routine Execution of ‘IRET’: 1) IP <= ((SP)) 2) SP <= (SP)+2 3) CS <= ((SP)) 4) SP <= (SP)+2 5) FR <= ((SP)) 6) SP <= (SP)+2 System Routine Application designers can perform I/O operation of I/O device by calling system routines. System routines are designed by system designers. Then, most application designers can focus on the application design. System Routine Application DOS Routine BIOS Routine System Routine INT 21H：DOS Routines INT 16H：BIOS Routines for keyboard INT 10H：BIOS Routines for display INT 13H：BIOS Routines for disk Parameter Transfer in System Routine Most system Routines use registers for parameter transferring. One must know parameter transfer agreement of a routine before one can use it. Original data of other registers before calling is protected as CPU execution scene by routines. System Routine Example 1: ; transfer sub-function number MOV AH，01H INT 21H This routine waits a keyboard input, and return the ASCII code of input key to register AL. System Routine Example 2: ; transfer ASCII code MOV DL， ‘A’ ; transfer sub-function number MOV AH， 02H INT 21H This routine outputs the given character at current cursor position in screen, and then adjust cursor position. System Routine Example 3: ; transfer sub-function number MOV AH, 4CH INT 21H This routine return CPU controlling to DOS (operating system).