/* ****************************************************************************************************** */
/*   											crt.s	                                                  */
/*                                                                                                        */
/*                       Assembly Language Startup Code for Atmel AT91SAM7S256                            */
/*                                                                                                    	  */
/*                                                                                           			  */
/*                                                                                                        */
/*                                                                                                        */
/* Author:  James P Lynch      May 12, 2007                                                               */
/* ****************************************************************************************************** */

/* Stack Sizes */
.set  UND_STACK_SIZE, 0x00000010		/* stack for "undefined instruction" interrupts is 16 bytes 	 */
.set  ABT_STACK_SIZE, 0x00000010		/* stack for "abort" interrupts is 16 bytes                 	 */
.set  FIQ_STACK_SIZE, 0x00000080		/* stack for "FIQ" interrupts  is 128 bytes     				 */
.set  IRQ_STACK_SIZE, 0X00000080		/* stack for "IRQ" normal interrupts is 128 bytes  				 */
.set  SVC_STACK_SIZE, 0x00000080		/* stack for "SVC" supervisor mode is 128 bytes  				 */

/* Standard definitions of Mode bits and Interrupt (I & F) flags in PSRs (program status registers) 	 */
.set  ARM_MODE_USR, 0x10            	/* Normal User Mode 											 */
.set  ARM_MODE_FIQ, 0x11            	/* FIQ Processing Fast Interrupts Mode 							 */
.set  ARM_MODE_IRQ, 0x12            	/* IRQ Processing Standard Interrupts Mode 						 */
.set  ARM_MODE_SVC, 0x13            	/* Supervisor Processing Software Interrupts Mode 				 */
.set  ARM_MODE_ABT, 0x17            	/* Abort Processing memory Faults Mode 							 */
.set  ARM_MODE_UND, 0x1B            	/* Undefined Processing Undefined Instructions Mode 			 */
.set  ARM_MODE_SYS, 0x1F            	/* System Running Priviledged Operating System Tasks  Mode		 */
.set  I_BIT, 0x80               		/* when I bit is set, IRQ is disabled (program status registers) */
.set  F_BIT, 0x40               		/* when F bit is set, FIQ is disabled (program status registers) */

/* Addresses and offsets of AIC and PIO  */
.set  AT91C_BASE_AIC, 0xFFFFF000 		/* (AIC) Base Address                         */
.set  AT91C_PIOA_CODR, 0xFFFFF434		/* (PIO) Clear Output Data Register           */
.set  AT91C_AIC_IVR, 0xFFFFF100			/* (AIC) IRQ Interrupt Vector Register        */
.set  AT91C_AIC_FVR, 0xFFFFF104			/* (AIC) FIQ Interrupt Vector Register        */
.set  AIC_IVR, 256						/* IRQ Vector Register offset from base above */
.set  AIC_FVR, 260						/* FIQ Vector Register offset from base above */
.set  AIC_EOICR, 304					/* End of Interrupt Command Register          */

/* identify all GLOBAL symbols  */
.global _vec_reset						
.global _vec_undef						
.global _vec_swi						
.global _vec_pabt						
.global _vec_dabt						
.global _vec_rsv						
.global _vec_irq						
.global _vec_fiq
.global AT91F_Irq_Handler
.global	AT91F_Fiq_Handler
.global	AT91F_Default_FIQ_handler
.global	AT91F_Default_IRQ_handler
.global	AT91F_Spurious_handler
.global	AT91F_Dabt_Handler
.global	AT91F_Pabt_Handler
.global	AT91F_Undef_Handler


/* GNU assembler controls  */
.text									/* all assembler code that follows will go into .text section	 */
.arm									/* compile for 32-bit ARM instruction set						 */
.align									/* align section on 32-bit boundary								 */

/* ============================================================ */
/* 						VECTOR TABLE     					 	*/
/*																*/
/*	Must be located in FLASH at address 0x00000000				*/
/*																*/
/*	Easy to do if this file crt.s is first in the list 			*/
/*	for the linker step in the makefile, e.g.					*/
/*																*/
/*	    $(LD) $(LFLAGS) -o main.out  crt.o main.o				*/
/*																*/
/* ============================================================ */

_vec_reset:		b           _init_reset				/* RESET vector - must be at 0x00000000	*/
_vec_undef:		b           AT91F_Undef_Handler		/* Undefined Instruction vector			*/
_vec_swi:		b           _vec_swi				/* Software Interrupt vector			*/
_vec_pabt:		b           AT91F_Pabt_Handler		/* Prefetch abort vector				*/
_vec_dabt:		b           AT91F_Dabt_Handler		/* Data abort vector					*/
_vec_rsv:		nop                     			/* Reserved vector						*/
_vec_irq:		b           AT91F_Irq_Handler		/* Interrupt Request (IRQ) vector		*/
_vec_fiq:		                         			/* Fast interrupt request (FIQ) vector	*/

/* ======================================================================== */
/* Function: 			AT91F_Fiq_Handler	       			 				*/
/*                                                                        	*/
/* The FIQ interrupt asserts when switch SW1 is pressed.                    */
/*																			*/
/* This simple FIQ handler turns on LED3 (Port PA2). The LED3 will be       */
/* turned off by the background loop in main() thus giving a visual         */
/* indication that the interrupt has occurred.                              */
/*																			*/
/* This FIQ_Handler supports non-nested FIQ interrupts (a FIQ interrupt 	*/
/* cannot itself be interrupted).											*/
/*	                                               							*/
/* The Fast Interrupt Vector Register (AIC_FVR) is read to clear the        */
/* interrupt.                                                             	*/
/*                                                                        	*/
/* A global variable FiqCount is also incremented.							*/
/*																			*/
/* Remember that switch SW1 is not debounced, so the FIQ interrupt may   	*/
/* occur more than once for a single button push.                           */
/*																			*/
/* Programmer: James P Lynch												*/
/* ======================================================================== */
AT91F_Fiq_Handler:

/* Adjust LR_irq */
				sub		lr, lr, #4

/* Read the AIC Fast Interrupt Vector register to clear the interrupt */
				ldr		r12, =AT91C_AIC_FVR
				ldr		r11, [r12]
				
/* Turn on LED3 (write 0x0008 to PIOA_CODR at 0xFFFFF434) */
				ldr		r12, =AT91C_PIOA_CODR
				mov		r11, #0x04
				str		r11, [r12]

/* Increment the _FiqCount variable */
				ldr		r12, =FiqCount
				ldr		r11, [r12]
				add		r11, r11, #1
				str		r11, [r12]

/* Return from Fiq interrupt */
				movs	pc, lr


/* ======================================================================== */
/* 				  _init_reset Handler                                       */
/*																            */
/*	 RESET vector 0x00000000 branches to here.                              */
/*	 															            */
/*	 ARM microprocessor begins execution after RESET at address 0x00000000	*/ 
/*   in Supervisor mode with interrupts disabled!							*/
/*	                                                                        */
/*	 _init_reset handler:  creates a stack for each ARM mode.               */
/*	                       sets up a stack pointer for each ARM mode.       */
/*	                       turns off interrupts in each mode.               */
/*						   leaves CPU in SYS (System) mode.                 */
/*	                                                   			            */
/*	                       block copies the initializers to .data section   */
/*						   clears the .bss section to zero	                */
/*	                                             				            */
/*						   branches to main( ) 					            */
/* ======================================================================== */
.text			/* all assembler code that follows will go into .text section	 */
.align			/* align section on 32-bit boundary								 */
_init_reset: 
				/* Setup a stack for each mode with interrupts initially disabled. */
    			ldr   r0, =_stack_end						/* r0 = top-of-stack  */
    			
    			msr   CPSR_c, #ARM_MODE_UND|I_BIT|F_BIT 	/* switch to Undefined Instruction Mode  */
    			mov   sp, r0								/* set stack pointer for UND mode  */
    			sub   r0, r0, #UND_STACK_SIZE				/* adjust r0 past UND stack  */
    			
    			msr   CPSR_c, #ARM_MODE_ABT|I_BIT|F_BIT 	/* switch to Abort Mode */
    			mov   sp, r0								/* set stack pointer for ABT mode  */
    			sub   r0, r0, #ABT_STACK_SIZE				/* adjust r0 past ABT stack  */
    			
    			msr   CPSR_c, #ARM_MODE_FIQ|I_BIT|F_BIT 	/* switch to FIQ Mode */
    			mov   sp, r0								/* set stack pointer for FIQ mode  */	
   				sub   r0, r0, #FIQ_STACK_SIZE				/* adjust r0 past FIQ stack  */
   				
    			msr   CPSR_c, #ARM_MODE_IRQ|I_BIT|F_BIT 	/* switch to IRQ Mode */