uart_rx.c

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

#include <stdio.h>

#include "pico/stdlib.h"
#include "pico/multicore.h"
#include "hardware/pio.h"
#include "hardware/uart.h"
#include "uart_rx.pio.h"

// This program
// - Uses UART1 (the spare UART, by default) to transmit some text
// - Uses a PIO state machine to receive that text
// - Prints out the received text to the default console (UART0)
// This might require some reconfiguration on boards where UART1 is the
// default UART.

#define SERIAL_BAUD PICO_DEFAULT_UART_BAUD_RATE
#define HARD_UART_INST uart1

// You'll need a wire from GPIO4 -> GPIO3
#define HARD_UART_TX_PIN 4
#define PIO_RX_PIN 3

// Check the pin is compatible with the platform
#if PIO_RX_PIN >= NUM_BANK0_GPIOS
#error Attempting to use a pin>=32 on a platform that does not support it
#endif

// Ask core 1 to print a string, to make things easier on core 0
void core1_main() {
    const char *s = (const char *) multicore_fifo_pop_blocking();
    uart_puts(HARD_UART_INST, s);
}

int main() {
    // Console output (also a UART, yes it's confusing)
    setup_default_uart();
    printf("Starting PIO UART RX example\n");

    // Set up the hard UART we're going to use to print characters
    uart_init(HARD_UART_INST, SERIAL_BAUD);
    gpio_set_function(HARD_UART_TX_PIN, GPIO_FUNC_UART);

    // Set up the state machine we're going to use to receive them.
    PIO pio;
    uint sm;
    uint offset;

    // This will find a free pio and state machine for our program and load it for us
    // We use pio_claim_free_sm_and_add_program_for_gpio_range (for_gpio_range variant)
    // so we will get a PIO instance suitable for addressing gpios >= 32 if needed and supported by the hardware
    bool success = pio_claim_free_sm_and_add_program_for_gpio_range(&uart_rx_program, &pio, &sm, &offset, PIO_RX_PIN, 1, true);
    hard_assert(success);

    uart_rx_program_init(pio, sm, offset, PIO_RX_PIN, SERIAL_BAUD);
    //uart_rx_mini_program_init(pio, sm, offset, PIO_RX_PIN, SERIAL_BAUD);

    // Tell core 1 to print some text to uart1 as fast as it can
    multicore_launch_core1(core1_main);
    const char *text = "Hello, world from PIO! (Plus 2 UARTs and 2 cores, for complex reasons)\n";
    multicore_fifo_push_blocking((uint32_t) text);

    // Echo characters received from PIO to the console
    while (true) {
        char c = uart_rx_program_getc(pio, sm);
        putchar(c);
    }

    // This will free resources and unload our program
    pio_remove_program_and_unclaim_sm(&uart_rx_program, pio, sm, offset);
}