UNIVERSITY OF CALIFORNIA, RIVERSIDE

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1 Final Page 1 of 7 UNIVERSITY OF CALIFORNIA, RIVERSIDE Computer Science Department CS61 Machine Organization & Assembly Language Final September 1, Name: Solution Key Student ID#: Please print legibly (Numbers in parenthesis denote total possible points for question.) 1. What is the value in the al register after the following program halts? (5) blue: yellow: red: white: Seven (7) lea push lea xor push lea push call inc ret inc ret inc halt bx, white bx bx, blue ax,ax bx bx, red bx yellow al al al

2 Final Page 2 of 7 2. Write the procedure that is equivalent to the following Pascal procedure using the standard convention for parameter passing. Use a far procedure and a far pointer for the variable i. procedure farproc (j, k, m : integer; var i : integer) // j, k, & m are passed by value // i is passed by reference begin i = j (k + m); end; (10) ; a far procedure(j,k,m : integer; var i : integer) ;this is the content of the stack far_j equ 14[bp] ;j is an integer = 2 bytes far_k equ 12[bp] ;k is an integer = 2 bytes far_m equ 10[bp] ;m is an integer = 2 bytes far_i equ 6[bp] ;i is a far pointer = 4 bytes ; equ 4[bp] ;segment of return address ; equ 2[bp] ;offset of return address ; equ 0[bp] ;original bp value farproc proc far push bp mov bp, sp push ax ;save registers that are changed in push bx ; procedure push es ; i := j - (k + m) les bx, far_i ;get address of i into ES:BX mov ax, far_j ;get value of j sub ax, far_k sub ax, far_m mov es:[bx], ax ;store result into i pop es ;restore original register values pop bx pop ax farproc pop bp ret 10 ;10 bytes total for all the parameters endp

3 Final Page 3 of 7 3. Given the following array declaration myarray word 2 dup (3 dup (1, 2, 3, 4, 5, 6)) write a segment of code that will sum all the numbers in the array and print out that sum on the screen. You can assume that a variable call TOTAL has been declared for storing the sum. Use 386 addressing modes to access the elements in the array. (10) mov ecx, 5 ;initialize ecx with 5 for the count mov ax, myarray ;initialize ax with the first number next: add ax, myarray[ecx*2] loop next ;will decrement cx until 0 ; print out the sum mov total, ax printf byte Sum is %i., cr, lf, 0 dword total ) 6 points for the sum code using the [ecx*2] addressing mode. ) 4 points for the sum code using 286 addressing mode. ) 4 points for the print code.

4 Final Page 4 of 7 4. Write a segment of code that is equivalent to the following case statement: (5) case i of 5: ax = 1; ; assign 1 to the ax register 8: ax = 2; 9: ax = 3; 10: ax = 4; otherwise: ax = 5; end move bx, i cmp bx, 5 jl other cmp bx, 10 jg other shl bx, 1 jmp JmpTbl[bx-10] JmpTbl word case5, other, other, case8, case9, case10 case5: mov ax, 1 case8: mov ax, 2 case9: mov ax, 3 case10: mov ax, 4 other: mov ax, 5 endcase:

5 Final Page 5 of 7 5. Assume that there are three signed integer variables J, K, and M. Write the code to perform the statement J := K / M (5) mov cwd idiv mov ax, K M J, ax ;sign extend signed value in ax to dx 6. Briefly describe the differences between polled I/O and interrupt driven I/O. (3) Polled I/O is when the CPU constantly tests a port to see if data is available, i.e. the CPU polls (asks) the port if it has data available or if it is capable of accepting data. For interrupt driven I/O the CPU doesn t have to constantly check the I/O device to see if it needs service. Instead, when the I/O device requires service from the CPU, it will send an interrupt signal to the CPU. This causes the CPU to interrupt the current instruction sequence and call a special interrupt service routine to service the I/O device.

6 Final Page 6 of 7 7. What hardware architectural method is used so that the CPU can complete one instruction per clock cycle? (3) Pipelining 8. What is a wait state? (3) A wait state is just an extra clock cycle that the CPU gives to slow devices to complete an operation. 9. The system bus is divided into three different buses. What are the names of these three buses? (3) Data bus, address bus, and control bus.

7 Final Page 7 of Show graphically the movement of data for the instruction (3) mov al, [bx+si] i.e. where it gets the data and where it stores it to. SI + AL BX + DS 11. Write a sample instruction that accesses data from (a) a memory-mapped I/O device, and (b) an I/O-mapped I/O device. (3) a) Any move (mov) instructions or arithmetic instructions that accesses memory. mov ax, 1234 b) The in and out instructions. in al, 60h