Datasheet

28 }
29 if (rx_remain && !pio_sm_is_rx_empty(spi->pio, spi->sm)) {
30 (void) *rxfifo;
31 --rx_remain;
32 }
33 }
34 }
Putting this all together, this complete C program will loop back some data through a PIO SPI at 1 MHz, with all four
CPOL/CPHA combinations:
Pico Examples: https://github.com/raspberrypi/pico-examples/tree/pre_release/pio/spi/spi_loopback.c Lines 1 - 77
Ê1 /**
Ê2 * Copyright (c) 2020 Raspberry Pi (Trading) Ltd.
Ê3 *
Ê4 * SPDX-License-Identifier: BSD-3-Clause
Ê5 */
Ê6
Ê7 #include <stdlib.h>
Ê8 #include <stdio.h>
Ê9
10 #include "pico/stdlib.h"
11 #include "pio_spi.h"
12
13 // This program instantiates a PIO SPI with each of the four possible
14 // CPOL/CPHA combinations, with the serial input and output pin mapped to the
15 // same GPIO. Any data written into the state machine's TX FIFO should then be
16 // serialised, deserialised, and reappear in the state machine's RX FIFO.
17
18 #define PIN_SCK 18
19 #define PIN_MOSI 16
20 #define PIN_MISO 16 // same as MOSI, so we get loopback
21
22 #define BUF_SIZE 20
23
24 void test(const pio_spi_inst_t *spi) {
25 static uint8_t txbuf[BUF_SIZE];
26 static uint8_t rxbuf[BUF_SIZE];
27 printf("TX:");
28 for (int i = 0; i < BUF_SIZE; ++i) {
29 txbuf[i] = rand() >> 16;
30 rxbuf[i] = 0;
31 printf(" %02x", (int) txbuf[i]);
32 }
33 printf("\n");
34
35 pio_spi_write8_read8_blocking(spi, txbuf, rxbuf, BUF_SIZE);
36
37 printf("RX:");
38 bool mismatch = false;
39 for (int i = 0; i < BUF_SIZE; ++i) {
40 printf(" %02x", (int) rxbuf[i]);
41 mismatch = mismatch || rxbuf[i] != txbuf[i];
42 }
43 if (mismatch)
44 printf("\nNope\n");
45 else
46 printf("\nOK\n");
47 }
48
49 int main() {
RP2040 Datasheet
3.6. Examples 346