; ***********************************************************************
; *									*
; *   Software Interrupt Handler for the Flash Program, First Version   *
; *									*
; ***********************************************************************

; Author:   John Zaitseff <J.Zaitseff@unsw.edu.au>
; Date:     28th May, 2003
; Version:  1.2

; This file contains the software interrupt handler for the first version
; of the Flash program (flash-v1.elf), as used in ELEC2041 Experiment 5.


; -----------------------------------------------------------------------
; The following code will be placed into the ".ospage" section, NOT into
; the ".text" section.  The GNU Linker will place the ".ospage" section at
; address 0x1000.

; Notice that the file boot-swi-v1.s also contains code that is placed
; into the ".ospage" section; see Figure 8 in ELEC2041 Experiment 5 to see
; how the GNU Linker handles this situation.

	.section .ospage, "awx"	; For "operating system" code


	.global swi_handler	; Make this label visible to other modules

swi_handler:			; Software Interrupt handler
				; This handler runs in Supervisor mode

; This very simple SWI handler expects the caller to initialise R0 to the
; "protected port" address and R1 to the byte to be written to that
; address, prior to the invocation of SWI.  Nothing useful is returned.

	strb	r1, [r0]	; Write the byte in R1 to "protected port" R0
	movs	pc, lr		; Return to caller (end of exception)


	.end