EE345L Spring 2002 Quiz1 Page 1 of 3Jonathan W. Valvano First:_________________ Last:_____________________March 6, 2002, 11:00am-11:50amThis is an open book, open notes exam. You must put your answers on these pages only, you can use theback. You have 50 minutes, so please allocate your time accordingly. Please read the entire quiz before starting.(20) Question 1. Find the sequence of execution that leads to the incorrect value being displayed. Display is afunction that is called from the foreground, while RTIHan is a background interrupt service routine periodicallyactivated by the RTIF flag. If the interrupt occurs at a bad time, and time is a certain value, then Display willoutput an incorrect value. Part a) Mark each line of executable C with a “1”, “2”, “3”,… symbol signifying the order of execution that yields abad display. Also specify the value of Time before the interrupt (there is more than one).unsigned short Time;// called from the foregroundvoid Display(void){ SCI_OutChar(Time/10+0x30); // tens SCI_OutChar(Time%10+0x30); // ones}#pragma interrupt_handler RTIHan()void RTIHan(void){ Time++; // 0 to 59 if(Time == 60) Time=0; RTIFLG = 0x80; }#pragma abs_address:0xfff0void (*RTI_vector[])()={RTIHan};#pragma end_abs_address Part b) Rewrite the Display function to eliminate the bug. (50) Question 2. You will write a software device driver for an input/output device. The output goes to a LCDdisplay, and the input comes from a keypad. The I/O data are ASCII characters. The ritual should set the directionregisters for ports A and B, initializing Port B to inputs. Your software should use busy-waiting (Gadfly)synchronization. All operations should be friendly. The hardware connections are as follows:PA7 --> start your software sets this high to start an I/O operationPA6 <-- done this signal goes high when the I/O operation is completePA5 --> R/W 1 means input, and 0 means outputPB7-PB0 <-> data bidirectional, output to display, input from keypadTo output a letter to the LCD, 1) set R/W to 0 2) make Port B outputs 3) write Port B with the 8-bit data to display, 4) set start high 5) wait for done to be 1 6) set start low 7) wait for done to be 0 8) make Port B inputs againTo input a letter from the keypad, 1) set R/W to 1 2) set start high 3) wait for done to be 1 4) read input data 5) set start low 6) wait for done to be 0EE345L Spring 2002 Quiz1 Page 2 of 3Part a) Show the C code that goes in the IO.h header file.Part b) Show the C code that goes in the IO.c implementation file.EE345L Spring 2002 Quiz1 Page 3 of 3(30) Question 3. The overall goal is to draw a picture of the stack that exists while in the middle of the RTIHan.Starting at the top of main, hand-execute this software system; main calls function; the RTI interrupt occurs atthe specified spot within function, and the RTIHan runs until the “show stack” comment. Local variables,parameters, and return values will be pushed on the stack. For each element pushed on the stack, give a generalsymbolic description (e.g., return pointer, old X, i1, f0) rather than its specific value (e.g., $F08A, $0000, 100, 4.) #pragma interrupt_handler RTIHan()void RTIHan(void){short i1;short static i2=100; i2--; i1 = i2;// show stack at this point if(i1 == 0 ) i2=100; RTIFLG = 0x80; }#pragma abs_address:0xfff0void (*RTI_vector[])()={RTIHan};#pragma end_abs_addressshort function(short f0){ short f1; f1 = f0+4; // interrupt occurs here return f1;}void main(void){ short m1; m1 = function(4); while(1){}}extern void _start();#pragma abs_address:0xfffevoid (*reset_vector[])()={_start};#pragma end_abs_address .area data--- 0000 L2: .blkb 2 .area idata--- 0000 0064 .word 100 .area text F03B 34 _RTIHan:: pshx F03C B775 tfr s,x F03E 1B9E leas -2,sp F040 FC0800 ldd L2 F043 830001 subd #1 F046 7C0800 std L2 F049 18011E0800 movw L2,-2,x ; // show stack at this point F04E ED1E ldy -2,x F050 8D0000 cpy #0 F053 2606 bne L3 F055 180300640800 movw #100,L2 F05B 180B800015 L3: movb #128,0x15 F060 B757 tfr x,s F062 30 pulx F063 0B rti .org 0xfff0 FFF0 _RTI_vector:: FFF0 F03B .word _RTIHan .area data .area text F064 _function:: F064 3B pshd F065 34 pshx F066 B775 tfr s,x F068 1B9E leas -2,sp F06A EC02 ldd 2,x F06C C30004 addd #4 F06F 6C1E std -2,x ; // interrupt occurs here F071 EC1E ldd -2,x F073 B757 tfr x,s F075 30 pulx F076 1B82 leas 2,sp F078 3D rts F07F 34 _main:: pshx F080 B775 tfr s,x F082 1B9C leas -4,sp F084 CC0004 ldd #4 F087 16F064 jsr _function F08A 6C1C std -4,x F08C B746 tfr d,y F08E 6D1E sty -2,x F090 20FE L7: bra L7 F092 B757 tfr x,s F094 30 pulx F095 3D rts .org 0xfffe FFFE _reset_vector:: FFFE F000 .word