Datasheet


NOTE
These programs do not control the chip select line; chip select is often implemented as a software-controlled GPIO,
due to wildly different behaviour between different SPI hardware. The full spi.pio source linked above contains some
examples how PIO can implement a hardware chip select line.
A C helper function configures the state machine, connects the GPIOs, and sets the state machine running. Note that
the SPI frame size — that is, the number of bits transferred for each FIFO record — can be programmed to any value
from 1 to 32, without modifying the program. Once configured, the state machine is set running.
Pico Examples: https://github.com/raspberrypi/pico-examples/tree/master/pio/spi/spi.pio Lines 46 - 72
46 static inline void pio_spi_init(PIO pio, uint sm, uint prog_offs, uint n_bits,
47 float clkdiv, bool cpha, bool cpol, uint pin_sck, uint pin_mosi, uint pin_miso) {
48 pio_sm_config c = cpha ? spi_cpha1_program_get_default_config(prog_offs) :
Ê spi_cpha0_program_get_default_config(prog_offs);
49 sm_config_set_out_pins(&c, pin_mosi, 1);
50 sm_config_set_in_pins(&c, pin_miso);
51 sm_config_set_sideset_pins(&c, pin_sck);
52 // Only support MSB-first in this example code (shift to left, auto push/pull,
Ê threshold=nbits)
53 sm_config_set_out_shift(&c, false, true, n_bits);
54 sm_config_set_in_shift(&c, false, true, n_bits);
55 sm_config_set_clkdiv(&c, clkdiv);
56
57 // MOSI, SCK output are low, MISO is input
58 pio_sm_set_pins_with_mask(pio, sm, 0, (1u << pin_sck) | (1u << pin_mosi));
59 pio_sm_set_pindirs_with_mask(pio, sm, (1u << pin_sck) | (1u << pin_mosi), (1u <<
Ê pin_sck) | (1u << pin_mosi) | (1u << pin_miso));
60 pio_gpio_init(pio, pin_mosi);
61 pio_gpio_init(pio, pin_miso);
62 pio_gpio_init(pio, pin_sck);
63
64 // The pin muxes can be configured to invert the output (among other things
65 // and this is a cheesy way to get CPOL=1
66 gpio_set_outover(pin_sck, cpol ? GPIO_OVERRIDE_INVERT : GPIO_OVERRIDE_NORMAL);
67 // SPI is synchronous, so bypass input synchroniser to reduce input delay.
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: https://github.com/raspberrypi/pico-examples/tree/master/pio/spi/pio_spi.c Lines 18 - 34
18 void __time_critical_func(pio_spi_write8_blocking)(const pio_spi_inst_t *spi, const uint8_t
Ê *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 365