spdif_rx_capture.pio

; Copyright (c) 2023, Elehobica
; Released under the BSD-2-Clause
; refer to https://opensource.org/licenses/BSD-2-Clause

; PIO program for direct sample of S/PDIF data
; sampled data is used for detection of sampling frequency

; ==============================================================================================
.program spdif_rx_capture

public entry_point:
    set x, 31
; block here if no signal
loop_wait_toggle:
    wait 0 pin 0
    wait 1 pin 0
    jmp x-- loop_wait_toggle

; one more wait turn to avoid spending 1 cyc by jmp
    wait 0 pin 0
    wait 1 pin 0
; here just after rising edge of pin

; output samples non-stop unless fifo gets full
.wrap_target
    in pins, 1
.wrap

; ==============================================================================================
% c-sdk {

static inline void spdif_rx_capture_program_init(PIO pio, uint sm, uint offset, uint entry_point, pio_sm_config (*get_default_config)(uint), uint pin)
{
    pio_sm_set_consecutive_pindirs(pio, sm, pin, 1, false);
    pio_gpio_init(pio, pin);
    gpio_pull_down(pin);
    gpio_set_inover(pin, GPIO_OVERRIDE_NORMAL);

    pio_sm_config sm_config = (*get_default_config)(offset);

    sm_config_set_clkdiv(&sm_config, 1);
    sm_config_set_jmp_pin(&sm_config, pin);
    sm_config_set_in_pins(&sm_config, pin); // PINCTRL_IN_BASE for wait
    sm_config_set_in_shift(&sm_config, false, true, 32); // shift_left, autopush, 32bit
    sm_config_set_fifo_join(&sm_config, PIO_FIFO_JOIN_RX);

    pio_sm_init(pio, sm, offset, &sm_config);
    pio_sm_set_pins(pio, sm, 0); // clear pins
    pio_sm_clear_fifos(pio, sm);
    pio_sm_drain_tx_fifo(pio, sm);

    pio_sm_set_enabled(pio, sm, true);

    pio_sm_exec(pio, sm, pio_encode_jmp(offset + entry_point));
}

%}