main.pio

.program bitbang0                   ; define program name
.side_set 1                         ; dedicate one of the five timing bits for the pinout value

; define some constants
.define public upkeep_instruction_count 4
/*.define public clock_divisor            1000*/
.define public clock_divisor            10

; python stuff from the example that "we don't have to worry about"
/*.lang_opt python sideset_init = pico.PIO.OUT_HIGH15*/
/*.lang_opt python out_init     = pico.PIO.OUT_HIGH16*/
/*.lang_opt python out_shiftdir = 1*/

// each cycle runs for delay_unit * fifo_value + 2 instructions


.wrap_target
    pull noblock        side 0  ; TODO: pull until last value (skip if queue has many)
    out x, 32           side 1

    mov y, x            side 1
offwait:
    jmp y-- offwait     side 1

    mov y, x            side 0
onwait:
    jmp y-- onwait      side 0
.wrap

% c-sdk {
// yoinked from https://github.com/raspberrypi/pico-examples/blob/master/pio/ws2812/ws2812.pio#L31-L47 and https://datasheets.raspberrypi.org/pico/raspberry-pi-pico-c-sdk.pdfpg 41
#include "hardware/clocks.h"

static inline float pio_clock_freq()
{
    return clock_get_hz(clk_sys);
}

static inline void bitbang0_init(
        PIO pio,                                                        // which of the two PIO instances we are using
        uint sm,                                                        // which (of four) state machine to use
        uint offset,                                                    // where the program is loaded (in the 5 bit address space, (but TODO actually 4 bc we stole a bit for the output value?))
        uint pin,                                                       // the pin to wiggle
        float freq                                                      // 'frequency or baud rate' of the output, whatever that means
    ) {

    pio_gpio_init(pio, pin);                                            // init the pin for pio usage
    pio_sm_set_consecutive_pindirs(pio, sm, pin, 1, true);              // set a range (of length one, aka one pin) to be output

    pio_sm_config c = bitbang0_program_get_default_config(offset);      // get the default config??????? which we will modify
    sm_config_set_sideset_pins(&c, pin);                                // set the sideset pin. we have .side_set 1 so its only one pin, but with .side_set 3 it would set three pins
    //sm_config_set_out_shift(&c, false, true, 32);                       // configure the out instruction
        //                      ^^^^^                                       false for shifting MSB first
        //                             ^^^^                                 true for autopullg MSB first
        //                                   ^^                             autopull trheshhold, aka number of bits before the OSR register is refilled from the fifo
    sm_config_set_fifo_join(&c, PIO_FIFO_JOIN_TX);                      // HELPPPP not documented in the datasheet

    int cycles_per_bit = 4;                                             // can use constants declared in assembly bc they were declared with `public`
    /*float div = clock_get_hz(clk_sys) / (freq * cycles_per_bit);        // some math to divide up the clock speed to get the correct bitrate*/
    float div = bitbang0_clock_divisor;
    sm_config_set_clkdiv(&c, div);                                      // divide the actual clock speed so the state machine ticks once every `div` core clocks

    pio_sm_init(pio, sm, offset, &c);                                   // load config into state machine and go to the start adress
    pio_sm_set_enabled(pio, sm, true);                                  // launch!
}
%}