systick.c

/*
 * This file is part of the Micro Python project, http://micropython.org/
 *
 * The MIT License (MIT)
 *
 * Copyright (c) 2013, 2014 Damien P. George
 *
 * 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 STM32_HAL_H

#include "py/obj.h"
#include "irq.h"
#include "systick.h"

// We provide our own version of HAL_Delay that calls __WFI while waiting, in
// order to reduce power consumption.
void HAL_Delay(uint32_t Delay) {
    if (query_irq() == IRQ_STATE_ENABLED) {
        // IRQs enabled, so can use systick counter to do the delay
        extern __IO uint32_t uwTick;
        uint32_t start = uwTick;
        // Wraparound of tick is taken care of by 2's complement arithmetic.
        while (uwTick - start < Delay) {
            // Enter sleep mode, waiting for (at least) the SysTick interrupt.
            __WFI();
        }
    } else {
        // IRQs disabled, so need to use a busy loop for the delay.
        // To prevent possible overflow of the counter we use a double loop.
        const uint32_t count_1ms = HAL_RCC_GetSysClockFreq() / 4000;
        for (int i = 0; i < Delay; i++) {
            for (uint32_t count = 0; ++count <= count_1ms;) {
            }
        }
    }
}

// delay for given number of microseconds
void sys_tick_udelay(uint32_t usec) {
    if (query_irq() == IRQ_STATE_ENABLED) {
        // IRQs enabled, so can use systick counter to do the delay
        uint32_t start = sys_tick_get_microseconds();
        while (sys_tick_get_microseconds() - start < usec) {
        }
    } else {
        // IRQs disabled, so need to use a busy loop for the delay
        // sys freq is always a multiple of 2MHz, so division here won't lose precision
        const uint32_t ucount = HAL_RCC_GetSysClockFreq() / 2000000 * usec / 2;
        for (uint32_t count = 0; ++count <= ucount;) {
        }
    }
}

bool sys_tick_has_passed(uint32_t start_tick, uint32_t delay_ms) {
    return HAL_GetTick() - start_tick >= delay_ms;
}

// waits until at least delay_ms milliseconds have passed from the sampling of
// startTick. Handles overflow properly. Assumes stc was taken from
// HAL_GetTick() some time before calling this function.
void sys_tick_wait_at_least(uint32_t start_tick, uint32_t delay_ms) {
    while (!sys_tick_has_passed(start_tick, delay_ms)) {
        __WFI(); // enter sleep mode, waiting for interrupt
    }
}

// The SysTick timer counts down at 168 MHz, so we can use that knowledge
// to grab a microsecond counter.
//
// We assume that HAL_GetTickis returns milliseconds.
uint32_t sys_tick_get_microseconds(void) {
    mp_uint_t irq_state = disable_irq();
    uint32_t counter = SysTick->VAL;
    uint32_t milliseconds = HAL_GetTick();
    uint32_t status  = SysTick->CTRL;
    enable_irq(irq_state);

    // It's still possible for the countflag bit to get set if the counter was
    // reloaded between reading VAL and reading CTRL. With interrupts  disabled
    // it definitely takes less than 50 HCLK cycles between reading VAL and
    // reading CTRL, so the test (counter > 50) is to cover the case where VAL
    // is +ve and very close to zero, and the COUNTFLAG bit is also set.
    if ((status & SysTick_CTRL_COUNTFLAG_Msk) && counter > 50) {
        // This means that the HW reloaded VAL between the time we read VAL and the
        // time we read CTRL, which implies that there is an interrupt pending
        // to increment the tick counter.
        milliseconds++;
    }
    uint32_t load = SysTick->LOAD;
    counter = load - counter; // Convert from decrementing to incrementing

    // ((load + 1) / 1000) is the number of counts per microsecond.
    //
    // counter / ((load + 1) / 1000) scales from the systick clock to microseconds
    // and is the same thing as (counter * 1000) / (load + 1)
    return milliseconds * 1000 + (counter * 1000) / (load + 1);
}