ffb_handshake.pio

; SET pin 0 should be mapped to your LED GPIO

.program ffb_handshake
    set y, 6            ; 7 groups of pulses in handshake;
                        ; set y=6 to loop 7 times

main_loop:
    pull                ; Pull delay and pulse count into OSR
    out x, 16           ; x = Delay between pulses, in 0.1 ms units

wait_between_pulses:
    nop [8]
    jmp x-- wait_between_pulses

    ; Send trigger pulses. 1 cycle = 10 us; 1 ms = 100 cycles
    out x, 16           ; x = Pulse count

send_pulse:
    set pins, 1 [1]     ; 20 ms; adapt-ffb joy uses 50 ms,
                        ; but 20 is more reliable
    set pins, 0 [16]    ; 180 ms including the jmp below
    jmp x-- send_pulse

    jmp y-- main_loop


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

// Set up the FFB handshake program. Uses only the trigger pin.
void ffb_handshake_program_init(
    PIO pio, uint sm, uint offset, uint freq, uint pin_trigger
    )
{
    pio_sm_config c = ffb_handshake_program_get_default_config(offset);
    sm_config_set_set_pins(&c, pin_trigger, 1);

    // Connect PIO to the trigger pin, and set its direction
    pio_gpio_init(pio, pin_trigger);
    pio_sm_set_consecutive_pindirs(pio, sm, pin_trigger, 1, true);

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

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