main.c

//#include "types.h"
#include <stdio.h>
#include <inttypes.h>
#include "pico/stdlib.h"
#include "hardware/gpio.h"
#include "hardware/spi.h"
#include "pico/bootrom.h"


#define LED_PIN              (25u)
#define SPI_PIN_MISO         (0u)
#define SPI_PIN_CS           (1u)
#define SPI_PIN_CLK          (2u)
#define SPI_PIN_MOSI         (3u)



// Shamelessly stolen from the button example.
#include "hardware/sync.h" // save_and_disable_interrupts()...
#include "hardware/structs/ioqspi.h"
#include "hardware/structs/sio.h"
bool __no_inline_not_in_flash_func(get_bootsel_button)(void)
{
	const uint CS_PIN_INDEX = 1;

	// Must disable interrupts, as interrupt handlers may be in flash, and we
	// are about to temporarily disable flash access!
	uint32_t flags = save_and_disable_interrupts();

	// Set chip select to Hi-Z
	hw_write_masked(&ioqspi_hw->io[CS_PIN_INDEX].ctrl,
					GPIO_OVERRIDE_LOW << IO_QSPI_GPIO_QSPI_SS_CTRL_OEOVER_LSB,
					IO_QSPI_GPIO_QSPI_SS_CTRL_OEOVER_BITS);

	// Note we can't call into any sleep functions in flash right now
	for (volatile int i = 0; i < 1000; ++i);

	// The HI GPIO registers in SIO can observe and control the 6 QSPI pins.
	// Note the button pulls the pin *low* when pressed.
	bool button_state = !(sio_hw->gpio_hi_in & (1u << CS_PIN_INDEX));

	// Need to restore the state of chip select, else we are going to have a
	// bad time when we return to code in flash!
	hw_write_masked(&ioqspi_hw->io[CS_PIN_INDEX].ctrl,
					GPIO_OVERRIDE_NORMAL << IO_QSPI_GPIO_QSPI_SS_CTRL_OEOVER_LSB,
					IO_QSPI_GPIO_QSPI_SS_CTRL_OEOVER_BITS);

	restore_interrupts(flags);

	return button_state;
}

int main(void)
{
	stdio_init_all();

	gpio_init(LED_PIN);
	gpio_put(LED_PIN, 0);
	gpio_set_dir(LED_PIN, GPIO_OUT);

	// The 3DS uses 16.756991 MHz.
	// The SDK for some reason picks the next lowest (15625000) clock
	// instead of the next highest (20833333).
	// 15625000 seems to work though.
	spi_init(spi0, 16756991);
	spi_set_format(spi0, 8, SPI_CPOL_1, SPI_CPHA_1, SPI_MSB_FIRST);
	spi_set_slave(spi0, true);
	gpio_set_function(SPI_PIN_MISO, GPIO_FUNC_SPI);
	gpio_set_function(SPI_PIN_CS, GPIO_FUNC_SPI);
	gpio_set_function(SPI_PIN_CLK, GPIO_FUNC_SPI);
	gpio_set_function(SPI_PIN_MOSI, GPIO_FUNC_SPI); 

	sleep_ms(1);

	/*do
	{
		gpio_put(LED_PIN, 1);

		uint8_t rxbuf[2];
		const uint8_t resp[2] = {0xBA, 0xBE};
		spi_read_blocking(spi0, 0xE1, rxbuf, 2);
		spi_write_blocking(spi0, resp, 2);

		printf("Hello from 3DS: %02" PRIX8 "%02" PRIX8 "\n", rxbuf[0], rxbuf[1]);
		gpio_put(LED_PIN, 0);
		sleep_ms(1000);
	} while(!get_bootsel_button());*/

	// SPICARD autopoll test.
	do
	{
		sleep_ms(1000);
	} while(!get_bootsel_button());

	gpio_put(LED_PIN, 1);
	uint8_t rxbuf;
	const uint8_t resp = 0x02;
	spi_read_blocking(spi0, 0xE2, &rxbuf, 1);
	spi_write_blocking(spi0, &resp, 1);
	printf("Hello from 3DS: %02" PRIX8 "\n", rxbuf);
	sleep_ms(1000);
	gpio_put(LED_PIN, 0);

	reset_usb_boot(0, 0);
}