Add assembly bare metal blink examble for rp2350.

Signed-off-by: jmug <u.g.a.mariano@gmail.com>

bare_metal/rp2350/blink/hello_world.s

@@ -0,0 +1,79 @@
+.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
+