button.c

/**
 * Copyright (c) 2020 Raspberry Pi (Trading) Ltd.
 *
 * SPDX-License-Identifier: BSD-3-Clause
 */

#include <stdio.h>
#include "pico/stdlib.h"
#include "hardware/gpio.h"
#include "hardware/sync.h"
#include "hardware/structs/ioqspi.h"
#include "hardware/structs/sio.h"

// This example blinks the Pico LED when the BOOTSEL button is pressed.
//
// Picoboard has a button attached to the flash CS pin, which the bootrom
// checks, and jumps straight to the USB bootcode if the button is pressed
// (pulling flash CS low). We can check this pin in by jumping to some code in
// SRAM (so that the XIP interface is not required), floating the flash CS
// pin, and observing whether it is pulled low.
//
// This doesn't work if others are trying to access flash at the same time,
// e.g. XIP streamer, or the other core.

bool __no_inline_not_in_flash_func(get_bootsel_button)() {
    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() {
#ifndef PICO_DEFAULT_LED_PIN
#warning picoboard/button example requires a board with a regular LED
#else
    gpio_init(PICO_DEFAULT_LED_PIN);
    gpio_set_dir(PICO_DEFAULT_LED_PIN, GPIO_OUT);
    while (true) {
        gpio_put(PICO_DEFAULT_LED_PIN, get_bootsel_button() ^ PICO_DEFAULT_LED_PIN_INVERTED);
        sleep_ms(10);
    }
#endif
}