I have written the following code for reading and outputting characters and strings and then converting the strings to lowercase and sorting the characters with bubble sort! When I run the code, the code loops infinitely without doing anything except reading and outputting the strings and characters. Can someone help me as to what I am doing wrong here? I think I am messing up with my registers.. Heres the code in the attachment! Thank you.
clshah2 0 Newbie Poster
AREA Serial, CODE, READONLY
EXPORT lab3
SER EQU 0x04 ; Serial Port
USTAT0 EQU 0x08 ; UART0 Status Register
TRANS EQU 0x0C ; Transmit Register
RECEIV EQU 0x10 ; Receive Register
BAUD EQU 0x14 ;
string = "--------------------",0
prompt = "Enter a string up to 20 characters long, then press Enter: ", 0
ALIGN
;---------------------------------------------------------------------
;---------------------------------------------------------------------
;---------------------------------------------------------------------
uart_init ; INITIALIZE UART
STMFD SP!,{lr} ; Store register lr on stack
LDR r1, =0x03FFD000 ; Load base address into r1
MOV r2, #0 ; Turn off serial port
STR r2, [r1, #SER] ; Contents of 0x3FFD004, stored into r2
LDR r1, =0x03FFD000 ; Load base address into r1
MOV r2, #3 ; Set port for 8 bits, 1 stop, 0 parity
STR r2, [r1] ; Store the value 3 into memory address 0x3FFD000
LDR r1, =0x03FFD000 ; Load base address into r1
MOV r2, #9 ; Turn on serial port
STR r2, [r1, #SER] ; Store the value 9 into memory address 0x3FFD004
LDR r1, =0x03FFD000 ; Load base address into r1
MOV r2, #162 ; Set to 9600 baud
MOV r2, r2, LSL #4 ; Left shift value 162 stored in r2 by
; 4 spots, and recopy into r2
STR r2, [r1, #BAUD] ; Store left shifted value in r2 into
; memory address 0x3FFD014
LDMFD SP!, {lr} ; Restore register lr from stack
MOV pc, lr
;---------------------------------------------------------------------
;---------------------------------------------------------------------
;---------------------------------------------------------------------
read_string ; READ STRING ENTERED BY USER UNTIL
; ENTER KEY IS REACHED
STMFD SP!,{r1-r12, lr} ; Store register lr on stack
STORE BL read_character
STRB r0, [r9] ; Store the byte
ADD r9, r9, #1
BL output_character ;Display the character
CMP r0, #13 ; Finish when the Enter key is pressed
BNE STORE
LDMFD SP!, {r1-r12, lr} ; Restore register lr from stack
MOV pc, lr
;---------------------------------------------------------------------
;---------------------------------------------------------------------
;---------------------------------------------------------------------
read_character
STMFD SP!, {r1-r12,lr} ; Store register lr on stack
LOOP LDR r1, =0x03FFD000
LDR r2, [r1, #USTAT0]
TST r2, #32
BEQ LOOP
LDR r0, [r1, #RECEIV]
LDMFD SP!, {r1-r12,lr} ; Restore register lr from stack
MOV pc, lr
;---------------------------------------------------------------------
;---------------------------------------------------------------------
;---------------------------------------------------------------------
output_character
STMFD SP!,{r1-r12, lr} ; Store register lr on stack
LOOP2 LDR r1, =0x03FFD000 ; Load memory address 0x03FFD000 into r1
LDR r2, [r1, #USTAT0] ; Load 0x03FFD004 into r2
TST r2, #64 ; Clear bit 6
BEQ LOOP2
STR r0, [r1, #TRANS] ; Store contents of 0x03FFD004 into r1
LDMFD SP!, {r1-r12, lr} ; Restore register lr from stack
MOV pc, lr
;---------------------------------------------------------------------
;---------------------------------------------------------------------
;---------------------------------------------------------------------
output_string ; SHOW STRING IN HYPERTERMINAL
; UNTIL IT REACH END
STMFD SP!,{r1-r12, lr} ; Store register lr on stack
DISPLAY LDRB r0, [r10], #1 ; Load the byte from address in r10 into r0
; and post-index r10 by 1
CMP r0, #0 ; Finish when the string comes to a 0
BEQ DONE2
BL output_character
B DISPLAY
DONE2 ; Branch here if null character is reached
LDMFD SP!, {r1-r12, lr} ; Restore register lr from stack
MOV pc, lr
;---------------------------------------------------------------------
;---------------------------------------------------------------------
;---------------------------------------------------------------------
convert_2_lowercase
STMFD SP!,{r1-r12, lr} ; Store register lr on stack
MOV r5, #65 ; r5 holds ascii value for capital A
MOV r6, #90 ; r6 holds ascii value for capital Z
LOOPZ CMP r0, #13 ; Compare contents of r3 to ascii value for ENTER
BEQ DONE ; If equal to SPACE, Branch to LOOPE and immediately increment
LOOPX CMP r0, r6 ; Compare r0 to Z
BLE LOOPY ; Branch to LOOPY if r0 < Z
B DONE ; Otherwise, Branch to DONE
LOOPY CMP r0, r5 ; Compare r0 to A
BLT DONE ; Branch to DONE if r0 < A
LOOPE ADD r0, r0, #31 ; Add 32 to acsii value in r3 and copy back to r3
STRB r0, [r0], #1 ; store value in r3 into memory address r0
CMP r0, #0 ; Compare post indexed r12 address to NULL
BEQ DONE ; Branch to DONE if r12=0
B LOOPZ ; If unequal, unconditional branch to LOOPZ
DONE ; Done
LDMFD SP!, {r1-r12, lr} ; Restore register lr from stack
MOV pc, lr
;---------------------------------------------------------------------
;---------------------------------------------------------------------
;---------------------------------------------------------------------
SORT
STMFD SP!,{lr} ; Store register lr on stack
SORT2 LDR r8, =string
COUNTER LDRB r12, [r8], #1
CMP r12, #0
BNE INCR
B SORT1
INCR MOV r6, #0
ADD r6, r6, #1
B COUNTER
SORT1 LDRB r1, [r8]
LDRB r2, [r8, #1]
CMP r1, r2
BLT DONEX
CHANGE STRB r2, [r8]
STRB r1, [r8, #1]
DONEX ADD r8, r8, #1
CMP r2, #0
BEQ NEXT
B SORT1
NEXT SUB r6, r6, #1
CMP r6, #0
BEQ DONE5
LDR r8, =string
B SORT1
DONE5 LDMFD SP!, {lr} ; Restore register lr from stack
MOV pc, lr
;---------------------------------------------------------------------
;---------------------------------------------------------------------
;---------------------------------------------------------------------
lab3
STMFD SP!,{lr} ; Store register lr on stack
BL uart_init ; Branch to uart_init
LDR r10, =prompt ; Prompts user
BL output_string
LDR r9, =string ; Loads string into r9
BL read_string
; ---------------------------------------------------------------------------------------------------------
BL convert_2_lowercase
LDR r10, =string
BL output_string
BL SORT
LDR r10, =string
BL output_string
LDMFD SP!,{lr}
MOV pc, lr
END- 1 Contributor
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