microsecond_timer_stm32.cpp

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/**
 * @file    microsecond_timer_stm32.cpp
 *
 * A single upcounting timer (currently TIM5) is used as a single timebase both for time
 * measurement and event scheduling.  This helps reduce jitter by not making another time
 * measurement at the time of scheduling.
 * 
 * This implementation only works on stm32 because it sets hardware registers directly.
 * ChibiOS doesn't support using timers in output compare mode, only PMW, so we have to 
 * manually configure the timer in outupt compare mode.
 * 
 * @date Dec 1, 2020
 * @author Matthew Kennedy, (c) 2012-2020
 */
 
#include "global.h"
 
#if EFI_PROD_CODE && HAL_USE_PWM
 
#include "port_microsecond_timer.h"
 
void portSetHardwareSchedulerTimer(efitick_t nowNt, efitick_t setTimeNt) {
    // This implementation doesn't need the current time, only the target time
    UNUSED(nowNt);
 
    pwm_lld_enable_channel(&SCHEDULER_PWM_DEVICE, 0, setTimeNt);
    pwmEnableChannelNotificationI(&SCHEDULER_PWM_DEVICE, 0);
}
 
static void hwTimerCallback(PWMDriver*) {
    pwmDisableChannelNotificationI(&SCHEDULER_PWM_DEVICE, 0);
    portMicrosecondTimerCallback();
}
 
static constexpr PWMConfig timerConfig = {
    .frequency = SCHEDULER_TIMER_FREQ,
    /* wanted timer period = 2^32 counts,
     * but driver set (period - 1) value to register
     * also period is uint32_t
     * So set it to zero so it will overlap to 0xffffffff when writen to register */
    .period = 0,
    .callback = nullptr,        // No update callback
    .channels = {
        {PWM_OUTPUT_DISABLED, hwTimerCallback}, // Channel 0 = timer callback, others unused
        {PWM_OUTPUT_DISABLED, nullptr},
        {PWM_OUTPUT_DISABLED, nullptr},
        {PWM_OUTPUT_DISABLED, nullptr}
    },
    .cr2 = 0,
    .bdtr = 0,
    .dier = 0
};
 
void portInitMicrosecondTimer() {
    pwmStart(&SCHEDULER_PWM_DEVICE, &timerConfig);
 
    // ChibiOS doesn't let you configure timers in output compare mode, only PWM mode.
    // We want to be able to set the compare register without waiting for an update event
    // (which would take 358 seconds at 12mhz timer speed), so we have to use normal upcounting
    // output compare mode instead.
    SCHEDULER_TIMER_DEVICE->CCMR1 = STM32_TIM_CCMR1_OC1M(1);
 
    /* TODO: implement for all possible TIMs */
    if (SCHEDULER_TIMER_DEVICE == TIM5) {
        /* stop timers clock when core is halted */
    #if defined(STM32F4XX) || defined (STM32F7XX)
        DBGMCU->APB1FZ |= DBGMCU_APB1_FZ_DBG_TIM5_STOP;
    #endif
        /* TODO: stm32h7? */
    }
}
 
uint32_t getTimeNowLowerNt() {
    // Using the same timer for measurement and scheduling improves
    // precision and reduces jitter.
    return SCHEDULER_TIMER_DEVICE->CNT;
}
 
#endif // EFI_PROD_CODE