how to make a light blink on a SAMC21-XPRO kit

head.S

	.thumb
	.text
	.global vector_table
vector_table:
	.word 0x20007FF0
	.word _start+1
	.word isr_lockup+1 // NMI
	.word isr_lockup+1

	.word isr_lockup+1
	.word isr_lockup+1
	.word isr_lockup+1
	.word isr_lockup+1

isr_lockup:
	b isr_lockup

	.global _start
_start:
	// Set up generic I/O
	ldr r2, =0x41000000
	ldr r0, =0x00008000
	str r0, [r2, #0x00] // DIR
	ldr r1, =0x00008000
	str r1, [r2, #0x10] // OUT

	// Looparoo
	1: str r1, [r2, #0x10] // OUT
	ldr r0, =0x00008000
	eor r1, r0
	ldr r0, =8000000/3/4
	2: sub r0, #1
	bne 2b
	b 1b
	.pool

	.bss