circuitpython/ports/mimxrt10xx/common-hal/neopixel_write/__init__.c

/*
 * This file is part of the MicroPython project, http://micropython.org/
 *
 * The MIT License (MIT)
 *
 * Copyright (c) 2019 Lucian Copeland for Adafruit Industries
 * Copyright (c) 2020 Artur Pacholec
 *
 * 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.
 */

#include "shared-bindings/neopixel_write/__init__.h"

#include "common-hal/microcontroller/Pin.h"
#include "supervisor/linker.h"
#include "supervisor/port.h"

uint64_t next_start_raw_ticks = 0;

//sysclock divisors
#define MAGIC_800_INT  900000  // ~1.11 us  -> 1.2  field
#define MAGIC_800_T0H  2800000  // ~0.36 us -> 0.44 field
#define MAGIC_800_T1H  1350000  // ~0.74 us -> 0.84 field

#pragma GCC push_options
#pragma GCC optimize ("Os")

void PLACE_IN_ITCM(common_hal_neopixel_write)(const digitalio_digitalinout_obj_t* digitalinout, uint8_t *pixels,
                                uint32_t numBytes) {
    uint8_t *p = pixels, *end = p + numBytes, pix = *p++, mask = 0x80;
    uint32_t start = 0;
    uint32_t cyc = 0;

    //assumes 800_000Hz frequency
    //Theoretical values here are 800_000 -> 1.25us, 2500000->0.4us, 1250000->0.8us
    //TODO: try to get dynamic weighting working again
    const uint32_t sys_freq = SystemCoreClock;
    const uint32_t interval = (sys_freq / MAGIC_800_INT);
    const uint32_t t0 = (sys_freq / MAGIC_800_T0H);
    const uint32_t t1 = (sys_freq / MAGIC_800_T1H);

    // Wait to make sure we don't append onto the last transmission. This should only be a tick or
    // two.
    while (port_get_raw_ticks(NULL) < next_start_raw_ticks) {}

    GPIO_Type *gpio = digitalinout->pin->gpio;
    const uint32_t pin = digitalinout->pin->number;

    __disable_irq();
    // Enable DWT in debug core. Useable when interrupts disabled, as opposed to Systick->VAL
    CoreDebug->DEMCR |= CoreDebug_DEMCR_TRCENA_Msk;
    DWT->CTRL |= DWT_CTRL_CYCCNTENA_Msk;
    DWT->CYCCNT = 0;

    for(;;) {
        cyc = (pix & mask) ? t1 : t0;
        start = DWT->CYCCNT;
        gpio->DR |= (1U << pin);
        while((DWT->CYCCNT - start) < cyc);
        gpio->DR &= ~(1U << pin);
        while((DWT->CYCCNT - start) < interval);
        if(!(mask >>= 1)) {
            if(p >= end) break;
            pix       = *p++;
            mask = 0x80;
        }
    }

    // Update the next start.
    next_start_raw_ticks = port_get_raw_ticks(NULL) + 4;

    // Enable interrupts again
    __enable_irq();
}

#pragma GCC pop_options