dac.pio

/*
 *
 * The MIT License (MIT)
 *
 * Copyright (c) 2022 guruthree
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in
 * all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
 * THE SOFTWARE.
 *
 */

// write out to VGA board DAC
// based on https://github.com/guruthree/pico-composite-PAL-colour/blob/main/dac.pio

.program dac

.wrap_target
    out pins, 5
    out y, 3 // discard the extra bits to keep everything 8 aligned
.wrap

% c-sdk {

// the VGA board DAC is 0.75 at 31
#define DIVISIONS_PER_VOLT (255/6.2)
// this won't get the proper 1 V peak for composite video
// but it is enough for about half brightness

#define DAC_PIN_COUNT 5
static inline void dac_program_init(PIO pio, uint sm, uint offset, uint pin_base, float divider) {
    for(uint i=pin_base; i<pin_base+DAC_PIN_COUNT; i++) {
        pio_gpio_init(pio, i);
    }
    pio_sm_set_consecutive_pindirs(pio, sm, pin_base, DAC_PIN_COUNT, true);

    pio_sm_config c = dac_program_get_default_config(offset); // get a default config, this function call is auto-generated

    // change # of bits here if we want to write a 32-bit word and then go through it
    sm_config_set_out_shift(&c, true, true, 32); // true - shift right, auto pull, # of bits

    sm_config_set_out_pins(&c, pin_base, DAC_PIN_COUNT);

    sm_config_set_clkdiv(&c, divider);

    // join the FIFO buffers to get more DMA throughput?
    // we use the transmit only so join RX to the TX?
    sm_config_set_fifo_join(&c, PIO_FIFO_JOIN_TX);

    pio_sm_init(pio, sm, offset, &c);
    pio_sm_clear_fifos(pio, sm);
    pio_sm_set_enabled(pio, sm, true);
}

%}