68 hwsetbitspio inputsyncbypass 1u pinmiso 69 70

68 hw_set_bits(&pio->input_sync_bypass, 1u << pin_miso);
69
70 pio_sm_init(pio, sm, prog_offs, &c);
71 pio_sm_set_enabled(pio, sm, true);
72 }
The state machine will now immediately begin to shift out any data appearing in the TX FIFO, and push received data
into the RX FIFO.
Pico Examples: Lines 18 - 34
18 void __time_critical_func(pio_spi_write8_blocking)( const pio_spi_inst_t *spi, const uint8_t
*src, size_t len) {
19 size_t tx_remain = len, rx_remain = len;
20 // Do 8 bit accesses on FIFO, so that write data is byte-replicated. This
21 // gets us the left-justification for free (for MSB-first shift-out)
22 io_rw_8 *txfifo = (io_rw_8 *) &spi->pio->txf[spi->sm];
23 io_rw_8 *rxfifo = (io_rw_8 *) &spi->pio->rxf[spi->sm];
24 while (tx_remain || rx_remain) {
25 if (tx_remain && !pio_sm_is_tx_fifo_full(spi->pio, spi->sm)) {
26 *txfifo = *src++;
27 --tx_remain;
RP2040 Datasheet
3.6. Examples 344

28 }
29 if (rx_remain && !pio_sm_is_rx_fifo_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 1MHz, with all four
CPOL/CPHA combinations:
Pico Examples: Lines 1 - 77
1 /**
2 * Copyright (c) 2020 Raspberry Pi (Trading) Ltd.
3 *
4 * SPDX-License-Identifier: BSD-3-Clause
5 */
6
7 #include <stdlib.h>
8 #include <stdio.h>
9
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 345

50 stdio_init_all();
51
52 pio_spi_inst_t spi = {
53 .pio = pio0,
54 .sm = 0
55 };
56 float clkdiv = 31 . 25 f; // 1 MHz @ 125 clk_sys
57 uint cpha0_prog_offs = pio_add_program(spi.pio, &spi_cpha0_program);
58 uint cpha1_prog_offs = pio_add_program(spi.pio, &spi_cpha1_program);
59
60 for ( int cpha = 0 ; cpha <= 1 ; ++cpha) {
61 for ( int cpol = 0 ; cpol <= 1 ; ++cpol) {
62 printf( "CPHA = %d, CPOL = %d\n" , cpha, cpol);
63 pio_spi_init(spi.pio, spi.sm,
64 cpha ? cpha1_prog_offs : cpha0_prog_offs,
65 8 , // 8 bits per SPI frame
66 clkdiv,
67 cpha,
68 cpol,
69 PIN_SCK,
70 PIN_MOSI,
71 PIN_MISO
72 );
73 test(&spi);
74 sleep_ms( 10 );
75 }
76 }
77 }
3.6.2. WS2812 LEDs
WS2812 LEDs are driven by a proprietary pulse-width serial format, with a wide positive pulse representing a "1" bit, and
narrow positive pulse a "0". Each LED has a serial input and a serial output; LEDs are connected in a chain, with each
serial input connected to the previous LED’s serial output.