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mbed-os/targets/TARGET_STM/us_ticker_16b.c

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/* mbed Microcontroller Library
* Copyright (c) 2006-2016 ARM Limited
*
* 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 <stddef.h>
#include "us_ticker_api.h"
#include "PeripheralNames.h"
#include "hal_tick.h"
// A 16-bit timer is used
#if TIM_MST_16BIT
TIM_HandleTypeDef TimMasterHandle;
volatile uint32_t SlaveCounter = 0;
volatile uint32_t oc_int_part = 0;
void us_ticker_init(void)
{
/* NOTE: assuming that HAL tick has already been initialized! */
}
uint32_t us_ticker_read()
{
uint16_t cntH_old, cntH, cntL;
do {
cntH_old = SlaveCounter;
/* SlaveCounter needs to be checked before AND after we read the
* current counter TIM_MST->CNT, in case it wraps around.
* there are 2 possible cases of wrap around
* 1) in case this function is interrupted by timer_irq_handler and
* the SlaveCounter is updated. In that case we will loop again.
* 2) in case this function is called from interrupt context during
* wrap-around condtion. That would prevent/delay the timer_irq_handler
* from being called so we need to locally check the FLAG_UPDATE and
* update the cntH accordingly. The SlaveCounter variable itself will
* be updated in the interrupt handler just after ...
*/
if (__HAL_TIM_GET_FLAG(&TimMasterHandle, TIM_FLAG_UPDATE) == SET) {
cntH_old += 1;
}
cntL = TIM_MST->CNT;
cntH = SlaveCounter;
if (__HAL_TIM_GET_FLAG(&TimMasterHandle, TIM_FLAG_UPDATE) == SET) {
cntH += 1;
}
} while(cntH_old != cntH);
// Glue the upper and lower part together to get a 32 bit timer
return (uint32_t)(cntH << 16 | cntL);
}
void us_ticker_set_interrupt(timestamp_t timestamp)
{
// NOTE: This function must be called with interrupts disabled to keep our
// timer interrupt setup atomic
// Set new output compare value
__HAL_TIM_SET_COMPARE(&TimMasterHandle, TIM_CHANNEL_1, timestamp & 0xFFFF);
// Ensure the compare event starts clear
__HAL_TIM_CLEAR_FLAG(&TimMasterHandle, TIM_FLAG_CC1);
// Enable IT
__HAL_TIM_ENABLE_IT(&TimMasterHandle, TIM_IT_CC1);
/* Set the number of timer wrap-around loops before the actual timestamp
* is reached. If the calculated delta time is more than halfway to the
* next compare event, check to see if a compare event has already been
* set, and if so, add one to the wrap-around count. This is done to
* ensure the correct wrap count is used in the corner cases where the
* 16 bit counter passes the compare value during the process of
* configuring this interrupt.
*
* Assumption: The time to execute this function is less than 32ms
* (otherwise incorrect behaviour could result)
*
* Consider the following corner cases:
* 1) timestamp is 1 us in the future:
* oc_int_part = 0 initially
* oc_int_part left at 0 because ((delta - 1) & 0xFFFF) < 0x8000
* Compare event should happen in 1 us and us_ticker_irq_handler()
* called
* 2) timestamp is 0x8000 us in the future:
* oc_int_part = 0 initially
* oc_int_part left at 0 because ((delta - 1) & 0xFFFF) < 0x8000
* There should be no possibility of the CC1 flag being set yet
* (see assumption above). When the compare event does occur in
* 32768 us, us_ticker_irq_handler() will be called
* 3) timestamp is 0x8001 us in the future:
* oc_int_part = 0 initially
* ((delta - 1) & 0xFFFF) >= 0x8000 but there should be no
* possibility of the CC1 flag being set yet (see assumption above),
* so oc_int_part will be left at 0, and when the compare event
* does occur in 32769 us, us_ticker_irq_handler() will be called
* 4) timestamp is 0x10000 us in the future:
* oc_int_part = 0 initially
* ((delta - 1) & 0xFFFF) >= 0x8000
* There are two subcases:
* a) The timer counter has not incremented past the compare
* value while setting up the interrupt. In this case, the
* CC1 flag will not be set, so oc_int_part will be
* left at 0, and when the compare event occurs in 65536 us,
* us_ticker_irq_handler() will be called
* b) The timer counter has JUST incremented past the compare
* value. In this case, the CC1 flag will be set, so
* oc_int_part will be incremented to 1, and the interrupt will
* occur immediately after this function returns, where
* oc_int_part will decrement to 0 without calling
* us_ticker_irq_handler(). Then about 65536 us later, the
* compare event will occur again, and us_ticker_irq_handler()
* will be called
* 5) timestamp is 0x10001 us in the future:
* oc_int_part = 1 initially
* oc_int_part left at 1 because ((delta - 1) & 0xFFFF) < 0x8000
* CC1 flag will not be set (see assumption above). In 1 us the
* compare event will cause an interrupt, where oc_int_part will be
* decremented to 0 without calling us_ticker_irq_handler(). Then
* about 65536 us later, the compare event will occur again, and
* us_ticker_irq_handler() will be called
* 6) timestamp is 0x18000 us in the future:
* oc_int_part = 1 initially
* oc_int_part left at 1 because ((delta - 1) & 0xFFFF) < 0x8000
* There should be no possibility of the CC1 flag being set yet
* (see assumption above). When the compare event does occur in
* 32768 us, oc_int_part will be decremented to 0 without calling
* us_ticker_irq_handler(). Then about 65536 us later, the
* compare event will occur again, and us_ticker_irq_handler() will
* be called
* 7) timestamp is 0x18001 us in the future:
* oc_int_part = 1 initially
* ((delta - 1) & 0xFFFF) >= 0x8000 but there should be no
* possibility of the CC1 flag being set yet (see assumption above),
* so oc_int_part will be left at 1, and when the compare event
* does occur in 32769 us, oc_int_part will be decremented to 0
* without calling us_ticker_irq_handler(). Then about 65536 us
* later, the compare event will occur again, and
* us_ticker_irq_handler() will be called
*
* delta - 1 is used because the timer compare event happens on the
* counter incrementing to match the compare value, and it won't occur
* immediately when the compare value is set to the current counter
* value.
*/
uint32_t current_time = us_ticker_read();
uint32_t delta = timestamp - current_time;
/* Note: The case of delta <= 0 is handled in MBED upper layer */
oc_int_part = (delta - 1) >> 16;
if ( ((delta - 1) & 0xFFFF) >= 0x8000 &&
__HAL_TIM_GET_FLAG(&TimMasterHandle, TIM_FLAG_CC1) == SET ) {
++oc_int_part;
/* NOTE: Instead of incrementing oc_int_part here, we could clear
* the CC1 flag, but then you'd have to wait to ensure the
* interrupt is knocked down before returning and reenabling
* interrupts. Since this is a rare case, it's not worth it
* to try and optimize it, and it keeps the code simpler and
* safer to just do this increment instead.
*/
}
}
void us_ticker_fire_interrupt(void)
{
/* When firing the event, the number of 16 bits counter wrap-ups (oc_int)
* must be re-initialized */
oc_int_part = 0;
HAL_TIM_GenerateEvent(&TimMasterHandle, TIM_EVENTSOURCE_CC1);
}
/* NOTE: must be called with interrupts disabled! */
void us_ticker_disable_interrupt(void)
{
__HAL_TIM_DISABLE_IT(&TimMasterHandle, TIM_IT_CC1);
}
/* NOTE: must be called with interrupts disabled! */
void us_ticker_clear_interrupt(void)
{
__HAL_TIM_CLEAR_FLAG(&TimMasterHandle, TIM_FLAG_CC1);
}
#endif // TIM_MST_16BIT
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