; ***********************************************************************
; *									*
; *    Convert Lower Case ASCII Into Upper Case (Assembly Language)     *
; *									*
; ***********************************************************************

; Authors:  Saeid Nooshabadi and John Zaitseff
; Date:     29th April, 2003
; Version:  1.4

; This very simple program converts the lower case character in "lower"
; into upper case by subtracting 0x20.  It is essentially the assembly
; language equivalent of chsub-c.c.  The essential points to note are the
; use of "ldrb" and "strb" to load and store the characters (bytes) and,
; of course, the subtraction instruction "sub".


; -----------------------------------------------------------------------
; Assembly-language preamble for the main module

	.text			; Executable code follows

_start: .global _start		; "_start" is required by the linker
	.global main		; "main" is our main program

	b	main		; Start running the main program


; -----------------------------------------------------------------------
; Start of the main program

; This program loads the character in the variable "lower", subtracts the
; constant 0x20 and stores the result in the variable "upper".

main:	ldr	r3, =lower	; Load the address of "lower" into R3
	ldrb	r0, [r3]	; R0 = 0x00000061 (the character 'a')

	sub	r0, r0, #0x20	; R0 = 'a' - 0x20 = 'A'

	ldr	r3, =upper	; Load the address of "upper" into R3
	strb	r0, [r3]	; Store the (byte) value in R0 to "upper".

exit:	mov	pc, lr		; Stop the program (and return to the OS)


; -----------------------------------------------------------------------
; Program variables (stored together with the code)

lower:	.byte	'a'		; Variable "lower"; 'a' is used as an example
upper:	.byte	0		; Variable "upper"


; -----------------------------------------------------------------------

	.end