IRQ handler for LPC23xx ARM microcontroller

irq_handler.s

.section .text, "ax"
.arm
IRQ_Handler:
	SUB	LR, LR, #4		@ Adjust LR_irq and push it
	STMFD	SP!, {LR}

	MRS	LR, SPSR		@ Save SPSR need to be saved for nested interrupt
	STMFD	SP!, {R0-R3,IP,LR}	@ Push scratch/used registers and SPSR
	LDR	R0, =LPC_BASE_VIC	@ Get the ISR address pointed by VIC_VectAddr
	LDR	R0, [R0, #VIC_Address]
	MSR	CPSR_c, #M_SVC		@ Enter SVC mode and enable Irq and Fiq

	STMFD	SP!, {LR}		@ Call the ISR
	MOV	LR, PC
	BX	R0
	LDMIA	SP!, {LR}

	MSR	CPSR_c, #M_IRQ | B_Irq	@ Enter IRQ mode and disable Irq
	LDMIA	SP!, {R0-R3,IP,LR}	@ Restore scratch/used registers and SPSR
	MSR	SPSR_cxsf, LR		@ Restore SPSR_irq

	LDR	LR, =LPC_BASE_VIC	@ Issue EOI command to the VIC
	STR	LR, [LR, #VIC_Address]

	LDMIA	SP!, {PC}^		@ Reruen from the IRQ handler