thumb
	area	moncode, code, readonly

GPIOB_BSRR	equ	0x40010C10	; Bit Set/Reset register
	extern	current_value
	export	timer_callback
		
timer_callback	proc	
	ldr	r2, =current_value
	ldr	r0, [r2]
	ldr	r3, =GPIOB_BSRR
	cbnz	r0, zero
	
; mise a 1 de PB1
	mov	r1, #0x00000002
	str	r1, [r3]
	mov	r1, #1
	str	r1,  [r2]
	bx	lr
	
; mise a 0 de PB1
zero	mov	r1, #0x00020000
	str	r1, [r3]
	mov	r1, #0
	str	r1,  [r2]
	bx	lr

	endp	
	end
; N.B. le registre BSRR est write-only, on ne peut pas le relire