.section .text

.equ rst_base,		0x40020000	// Subsystems reset reg base 7.5.3
.equ rst_clr,		0x40023000 	// Adding 0x3000 according 2.1.3
.equ io_bank,		0x40028000
.equ io_bank_gp25,	0x400280cc
.equ sio_base, 		0xd0000000
.equ big_num,		0x00f00000	// For the delay.
.equ pads_base,		0x40038000  // Pad control registers base.
.equ pads_set,		0x4003a000
.equ pads_clr,		0x4003b000
.equ resets_wrd,	0b100001001000000 // Bits 14 (PLL_SYS), 9 (PADS_BANK0) and 6 (IO_BANK0)

.thumb_func // This makes sure that the address of start has its LSB set to signal thumb mode.
.global hello_start
hello_start:
// Bring PLL, PADS and IO out of reset
	ldr r0, =rst_clr
	ldr r2, =resets_wrd
	str r2, [r0, #0]
check_rst:
	ldr r0, =rst_base
	ldr r1, [r0, #0x8]		// Offset to RESET_DONE from rst_base
	and r1, r1, r2			// Check bit 14, 9 and 6 to ensure the subsystems we care about are out of reset.
	cmp r1, r2
	bne check_rst
clocks_setup:
// TODO: Configure the crystal oscilator and set it as the reference clock.
// TODO: Configure the PLL and wait for it to lock.
// TODO: Change the sys clock source to the PLL.
configure_peripheral:		
	// See: https://github.com/raspberrypi/pico-sdk/blob/ee68c78d0afae2b69c03ae1a72bf5cc267a2d94c/src/rp2_common/hardware_gpio/gpio.c#L38
	// Set pad input and output enabled.
	ldr r0, =pads_set
	mov r2, #0b1000000		// Set bit 6 to enable input.
	str r2, [r0, #0x68]
	ldr r0, =pads_clr
	mov r2, #0b10000000		// Clear bit 7 to enable output.
	str r2, [r0, #0x68]
	// Set function 5 (SIO) to GPIO25
	ldr r0, =io_bank_gp25
	mov r1, #5				// FSEL 5 (SIO)
	str r1, [r0]
	// Remove isolation control on the pad control now that it's connected to its peripheral (SIO).
	ldr r0, =pads_clr
	mov r2, #1				// Clear bit 8 to remove isolation control.
	lsl r2, r2, #8
	str r2, [r0, #0x68]
	// Enable the output
	ldr r0, =sio_base
	mov r1, #1
	lsl r1, r1, #25			// Only enable gpio25
	str r1, [r0, #0x38]		// GPIO_OE_SET offset
blink:
	ldr r0, =sio_base
	mov r1, #1
	lsl r1, r1, #25
led_loop:
	str r1, [r0, #0x18] // GPIO_OUT_SET
	ldr r3, =big_num
	bl delay

	str r1, [r0, #0x20] // GPIO_OUT_CLR
	ldr r3, =big_num
	bl delay

	b led_loop

delay:
	sub r3, #1
	bne delay
	bx lr

// An interrupt handler that just spins.
.thumb_func
.global isr_default
isr_default:
	b isr_default