;
; Copyright (c) 2021 mjcross
;
; SPDX-License-Identifier: BSD-3-Clause
;


.program nec_carrier_burst

; Generate bursts of carrier.
;
; Repeatedly wait for an IRQ to be set then clear it and generate 21 cycles of
; carrier with 25% duty cycle
;
.define NUM_CYCLES 21               ; how many carrier cycles to generate
.define BURST_IRQ 7                 ; which IRQ should trigger a carrier burst
.define public TICKS_PER_LOOP 4     ; the number of instructions in the loop (for timing)

.wrap_target
    set X, (NUM_CYCLES - 1)         ; initialise the loop counter
    wait 1 irq BURST_IRQ            ; wait for the IRQ then clear it
cycle_loop:
    set pins, 1                     ; set the pin high (1 cycle)
    set pins, 0 [1]                 ; set the pin low (2 cycles)
    jmp X--, cycle_loop             ; (1 more cycle)
.wrap


% c-sdk {
static inline void nec_carrier_burst_program_init(PIO pio, uint sm, uint offset, uint pin, float freq) {
    // Create a new state machine configuration
    //
    pio_sm_config c = nec_carrier_burst_program_get_default_config (offset);

    // Map the SET pin group to one pin, namely the `pin`
    // parameter to this function.
    //
    sm_config_set_set_pins (&c, pin, 1);

    // Set the GPIO function of the pin (connect the PIO to the pad)
    //
    pio_gpio_init (pio, pin);

    // Set the pin direction to output at the PIO
    //
    pio_sm_set_consecutive_pindirs (pio, sm, pin, 1, true);

    // Set the clock divider to generate the required frequency
    //
    float div = clock_get_hz (clk_sys) / (freq * nec_carrier_burst_TICKS_PER_LOOP);
    sm_config_set_clkdiv (&c, div);

    // Apply the configuration to the state machine
    //
    pio_sm_init (pio, sm, offset, &c);

    // Set the state machine running
    //
    pio_sm_set_enabled (pio, sm, true);
}
%}