read_joystick.pio

.program read_joystick
    set pins, 1 [19]    ; Trigger pulse notifies joystick to send data
    set pins, 0

    set x, 15           ; Acquire 16 bits each from 3 data pins
get_bit:
    wait 0 gpio 3       ; Wait for clock low: data is most stable here
    in pins, 3
    wait 1 gpio 3       ; Wait for clock high
    jmp x-- get_bit

    irq wait 0          ; All data is gathered, so send IRQ

    set x, 31           ; Cooldown before triggering again
wait_loop:
    nop [31]
    nop [31]
    jmp x-- wait_loop


% c-sdk {
#include "hardware/clocks.h"

// Set up the FFB handshake program. Uses only the trigger pin.
void read_joystick_program_init(
    PIO pio, uint sm, uint offset, uint freq,
    uint pin_trigger, uint pin_clk, uint pin_d0, uint pin_d1, uint pin_d2
    )
{
    pio_sm_config c = read_joystick_program_get_default_config(offset);
    sm_config_set_set_pins(&c, pin_trigger, 1);
    sm_config_set_in_pins(&c, pin_d0);
    sm_config_set_in_shift(&c, true, true, 24);
    sm_config_set_fifo_join(&c, PIO_FIFO_JOIN_RX);

    // Connect PIO to the trigger pin, and set its direction
    pio_gpio_init(pio, pin_trigger);
    pio_gpio_init(pio, pin_clk);
    pio_gpio_init(pio, pin_d0);
    pio_gpio_init(pio, pin_d1);
    pio_gpio_init(pio, pin_d2);
    pio_sm_set_consecutive_pindirs(pio, sm, pin_trigger, 1, true);
    pio_sm_set_consecutive_pindirs(pio, sm, pin_clk, 1, false);
    pio_sm_set_consecutive_pindirs(pio, sm, pin_d0, 3, false);

    float div = clock_get_hz(clk_sys) / freq;
    sm_config_set_clkdiv(&c, div);

    pio_sm_init(pio, sm, offset, &c);
}
%}