TIn 1: Feedback Laboratories. Lecture 4 Data transfer. Question: What is the IP? Institut für Embedded Systems. Institut für Embedded Systems

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1 Mitglied der Zürcher Fachhochschule TIn 1: Lecture 4 Data transfer Feedback Laboratories Question: What is the IP? Why do we NEED an IP?

2 Lecture 3: Lernziele Moving data, the why s and wherefores Moving data We have been confronted with the MOV operation Why do we need a move operation? Because we have to tell the processor precisely what to do AND Because there is no ability to perform operations directly on operands in memory. A large part of the job of a computer is to manipulate input data and produce output data From our Print Hello World we see that we are shifting an array or a block of bytes We would therefore expect that moving data from place to place is an important operation therefore we need a primitive for this.

3 Moving data The most powerful tool for moving data is a pointer What is the transfer size of Mov AL, 50H 8 bit of course What is the transfer size of Mov [DX], 50H And where does it go? Moving data MOV [DX], 50H goes to the DATA SEGMENT MOV CS:[DX], 50H goes to the code segement Will this work? What does this MOV BYTE PTR ES:[DX], 50H do? Is BYTE PRT (WORD PTR) and ES (DS, CS, SS) an processor command?

4 Exercise: Convert this to assembler code. public char print_array[] = { H, e, l, l, o,, W, o, r, l, d }; for (int i=1; i<=11; i++) { System.out.print(print_array[i]); }; Es gibt Lösungen.

5 ..... print_array DB H, e, l, l, o,, W, o, r, l, d LOOP_SIZE EQU 0BH MOV CX, 01H ;-- java int = 32-bit but we don't need 32 bits it so we ;-- assume short and use CX because i is a counting variable. for_loop: CMP CX, LOOP_SIZE ; -- in a for loop test before carrying out commands JZ end_loop ; -- end loop MOV DX, print_array ; --- get address of data ADD DX, CX ; get current offset result in DX MOV AL, [DX] ; ASSUME parameter given to System.out.print is in AL CALL System_out_print ; Assembler probably won't accept (.) as a separator ; so use underscores INC CX ; increment i JMP for_loop ; Unconditional Jump end_loop: es gibt Lösungen

6 .... print_array DB H, e, l, l, o,, W, o, r, l, d LOOP_SIZE EQU 0BH init_loop: MOV SI, 01H ; --- put it in the SOURCE index register (4 clocks) MOV BX, print_array ; --- put address in the base register (4 clocks) for_loop: CMP SI, LOOP_SIZE ; -- (4 clocks) JZ end_loop ; -- (16 clocks for a jump, 4 for a "fall through" MOV AL, [BX+SI] ; --- (10 clocks) CALL System_out_print ; --- (19 Clocks) INC SI ; --- increment DI ( 3 clocks) JMP for_loop ; --- Unconditional Jump (15 clocks) end_loop: ; --- for running loop = 45 clocks ; 8 clocks for initalisation Comments The use of Base and Index register is elegant but the use of two jumps less so Exercise Write the code to use only one jump.

7 und es gibt Lösungen.! print_array DB H, e, l, l, o,, W, o, r, l, d LOOP_SIZE EQU 0BH init_conditions: CLD MOV SI, print_array + 1 MOV CX, LOOP_SIZE ; --- clear direction flag (2 clocks) ; --- move address into SI (4 clocks) (i=1) ; (4 clocks) for_loop: LODS BYTE CALL System_out_print LOOP for_loop ; -- LODS loads the byte pointed to by SI into AL ; -- then it increments SI while direction Flag DF = 0 (12 clocks) ; (19 clocks)

8 The final consequence Give the commands LOOP and LODS to the hardware to perform. Procedure is called Direct Memory Access A little more on pointers We have seen that there are reigisters BP, SI, DI Abb 8.1

9 A little more on data movement There is also the operation XCHG AX, BX As well as IN AX, DX Which should be IN AX, [DX] but isn t OUT 054H, AX Shift Wir haben diverse Befehlsgruppen behandelt Daten Bewegungs Befehle IN/OUT, MOV, XCHG Logische Befehle AND, NOT, OR Sprung Befehle CALL, JMP Mathematische Befehle ADD (SUB, MUL)

10 Shift/Rotate Es gibt eine weitere Reihe von Befehle die SHIFT und ROTATE Befehle die auf einen Byte oder Word agieren. Shift entspricht einen Schieberegister bei den die neuen Stellen mit NULL gefüllt werden Rotate entspricht einen Schieberegister aber die einzelnen bits werden neue Positionen zugefügt. Einen XCHG AH, AL kann auch mit einen ROTATE AX, 8 Erledigt werden Shift/Rotate Einen Shift dagegen entspricht auch eine Multiplikation durch eine 2er Potenz. Erinnere (Segment Register * 10H) + Offset register = EA Also 2000:0200 = 2000* 10H = H = H (EA) Ist gleich wie 2000 << 4 = Für 2er Potenz Operationen ist einen Shift also effektiver als ein Multiplikation

11 Shift Beispiel 1