Question 16 (20 points) Complete the following assembly, by filling the numbered blanks, to implement a function that gets a string of characters from the keyboard using polling. Assume the following memory-mapped keyboard registers: Address 7 6 5 4 3 2 1 0 Ox4000 KBD_DATA Ox4004 KIN KIRQ KBD_STATUS 0x4008 KIE KBD_CONT Assume the following C function prototypes: // reads a string from the keyboard into buf, terminating when CR is read, and returns its length int gets (char* buf); // returns a character read from the keyboard char getc(); Further assume: That function parameters are passed and values returned in RO. KBD_DATA stores the most recently typed character KIN is set to indicate data is ready to be read; KIRQ is set to indicate that an interrupt has been requested KIE is set to enable interrupts CR (13) is the carriage return character kbd: .word 0x00004000 buf: .space 80 .equ CR, 13 main: LDR A1, gets 11 (1) // (2) gets: // (3) 11 (4) MOV MOV vi, V2, #0 getc: // (7) // (8) getcLoop: LDR Vi, LDRB A1, [V1, #4] TST A1, #2 BEQ getcLoop LDRB // (9) // (10) BX LR Blank # 1 Blank #2 Blank # 3 Blank #4 Blank # 5 Blank # 6 Blank #7 Blank #8 Blank #9 Blank # 10 Question 16 (20 points) Complete the following assembly, by filling the numbered blanks, to implement a function that gets a string of characters from the keyboard using polling. Assume the following memory-mapped keyboard registers: Address 7 6 5 4 3 2 1 0 Ox4000 KBD_DATA Ox4004 KIN KIRQ KBD_STATUS 0x4008 KIE KBD_CONT Assume the following C function prototypes: // reads a string from the keyboard into buf, terminating when CR is read, and returns its length int gets (char* buf); // returns a character read from the keyboard char getc(); Further assume: That function parameters are passed and values returned in RO. KBD_DATA stores the most recently typed character KIN is set to indicate data is ready to be read; KIRQ is set to indicate that an interrupt has been requested KIE is set to enable interrupts CR (13) is the carriage return character kbd: .word 0x00004000 buf: .space 80 .equ CR, 13 main: LDR A1, gets 11 (1) // (2) gets: // (3) 11 (4) MOV MOV vi, V2, #0 getc: // (7) // (8) getcLoop: LDR Vi, LDRB A1, [V1, #4] TST A1, #2 BEQ getcLoop LDRB // (9) // (10) BX LR Blank # 1 Blank #2 Blank # 3 Blank #4 Blank # 5 Blank # 6 Blank #7 Blank #8 Blank #9 Blank # 10