mbed-os/targets/TARGET_NUVOTON/TARGET_M451/us_ticker.c

/* mbed Microcontroller Library
 * Copyright (c) 2015-2016 Nuvoton
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

#include "us_ticker_api.h"
#include "sleep_api.h"
#include "mbed_assert.h"
#include "nu_modutil.h"
#include "nu_miscutil.h"

/* Micro seconds per second */
#define NU_US_PER_SEC               1000000
/* Timer clock per us_ticker tick */
#define NU_TMRCLK_PER_TICK          1
/* Timer clock per second */
#define NU_TMRCLK_PER_SEC           (1000 * 1000)
/* Timer max counter bit size */
#define NU_TMR_MAXCNT_BITSIZE       24
/* Timer max counter */
#define NU_TMR_MAXCNT               ((1 << NU_TMR_MAXCNT_BITSIZE) - 1)

static void tmr0_vec(void);

static const struct nu_modinit_s timer0_modinit = {TIMER_0, TMR0_MODULE, CLK_CLKSEL1_TMR0SEL_PCLK0, 0, TMR0_RST, TMR0_IRQn, (void *) tmr0_vec};

#define TIMER_MODINIT      timer0_modinit

static int ticker_inited = 0;

#define TMR_CMP_MIN         2
#define TMR_CMP_MAX         0xFFFFFFu

void us_ticker_init(void)
{
    if (ticker_inited) {
        return;
    }
    ticker_inited = 1;

    // Reset IP
    SYS_ResetModule(TIMER_MODINIT.rsetidx);

    // Select IP clock source
    CLK_SetModuleClock(TIMER_MODINIT.clkidx, TIMER_MODINIT.clksrc, TIMER_MODINIT.clkdiv);

    // Enable IP clock
    CLK_EnableModuleClock(TIMER_MODINIT.clkidx);

    TIMER_T *timer_base = (TIMER_T *) NU_MODBASE(TIMER_MODINIT.modname);

    // Timer for normal counter
    uint32_t clk_timer = TIMER_GetModuleClock(timer_base);
    uint32_t prescale_timer = clk_timer / NU_TMRCLK_PER_SEC - 1;
    MBED_ASSERT((prescale_timer != (uint32_t) -1) && prescale_timer <= 127);
    MBED_ASSERT((clk_timer % NU_TMRCLK_PER_SEC) == 0);
    uint32_t cmp_timer = TMR_CMP_MAX;
    MBED_ASSERT(cmp_timer >= TMR_CMP_MIN && cmp_timer <= TMR_CMP_MAX);
    // NOTE: TIMER_CTL_CNTDATEN_Msk exists in NUC472, but not in M451. In M451, TIMER_CNT is updated continuously by default.
    timer_base->CTL = TIMER_CONTINUOUS_MODE | prescale_timer/* | TIMER_CTL_CNTDATEN_Msk*/;
    timer_base->CMP = cmp_timer;

    NVIC_SetVector(TIMER_MODINIT.irq_n, (uint32_t) TIMER_MODINIT.var);

    NVIC_EnableIRQ(TIMER_MODINIT.irq_n);

    TIMER_EnableInt(timer_base);

    TIMER_Start(timer_base);
    /* Wait for timer to start counting and raise active flag */
    while(! (timer_base->CTL & TIMER_CTL_ACTSTS_Msk));
}

uint32_t us_ticker_read()
{
    if (! ticker_inited) {
        us_ticker_init();
    }

    TIMER_T *timer_base = (TIMER_T *) NU_MODBASE(TIMER_MODINIT.modname);

    return  (TIMER_GetCounter(timer_base) / NU_TMRCLK_PER_TICK);
}

void us_ticker_set_interrupt(timestamp_t timestamp)
{
    /* In continuous mode, counter will be reset to zero with the following sequence: 
     * 1. Stop counting
     * 2. Configure new CMP value
     * 3. Restart counting
     *
     * This behavior is not what we want. To fix it, we could configure new CMP value
     * without stopping counting first.
     */
    TIMER_T *timer_base = (TIMER_T *) NU_MODBASE(TIMER_MODINIT.modname);

    /* NOTE: Because H/W timer requests min compare value, our implementation would have alarm delay of 
     *       (TMR_CMP_MIN - interval_clk) clocks when interval_clk is between [1, TMR_CMP_MIN). */
    uint32_t cmp_timer = timestamp * NU_TMRCLK_PER_TICK;
    cmp_timer = NU_CLAMP(cmp_timer, TMR_CMP_MIN, TMR_CMP_MAX);
    timer_base->CMP = cmp_timer;
}

void us_ticker_disable_interrupt(void)
{
    TIMER_DisableInt((TIMER_T *) NU_MODBASE(TIMER_MODINIT.modname));
}

void us_ticker_clear_interrupt(void)
{
    TIMER_ClearIntFlag((TIMER_T *) NU_MODBASE(TIMER_MODINIT.modname));
}

void us_ticker_fire_interrupt(void)
{
    // NOTE: This event was in the past. Set the interrupt as pending, but don't process it here.
    //       This prevents a recursive loop under heavy load which can lead to a stack overflow.
    NVIC_SetPendingIRQ(TIMER_MODINIT.irq_n);
}

const ticker_info_t* us_ticker_get_info()
{
    static const ticker_info_t info = {
        NU_TMRCLK_PER_SEC / NU_TMRCLK_PER_TICK,
        NU_TMR_MAXCNT_BITSIZE
    };
    return &info;
}

static void tmr0_vec(void)
{
    TIMER_ClearIntFlag((TIMER_T *) NU_MODBASE(TIMER_MODINIT.modname));
    
    // NOTE: us_ticker_set_interrupt() may get called in us_ticker_irq_handler();
    us_ticker_irq_handler();
}