Gordon Craig
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Diff: targets/TARGET_STM/us_ticker_16b.c
- Revision:
- 167:e84263d55307
- Parent:
- 165:e614a9f1c9e2
--- a/targets/TARGET_STM/us_ticker_16b.c Thu Jun 08 15:02:37 2017 +0100
+++ b/targets/TARGET_STM/us_ticker_16b.c Wed Jun 21 17:46:44 2017 +0100
@@ -25,21 +25,9 @@
volatile uint32_t SlaveCounter = 0;
volatile uint32_t oc_int_part = 0;
-volatile uint16_t oc_rem_part = 0;
-volatile uint8_t tim_it_update; // TIM_IT_UPDATE event flag set in timer_irq_handler()
-volatile uint32_t tim_it_counter = 0; // Time stamp to be updated by timer_irq_handler()
static int us_ticker_inited = 0;
-void set_compare(uint16_t count)
-{
- TimMasterHandle.Instance = TIM_MST;
- // Set new output compare value
- __HAL_TIM_SET_COMPARE(&TimMasterHandle, TIM_CHANNEL_1, count);
- // Enable IT
- __HAL_TIM_ENABLE_IT(&TimMasterHandle, TIM_IT_CC1);
-}
-
void us_ticker_init(void)
{
if (us_ticker_inited) return;
@@ -52,22 +40,22 @@
uint32_t us_ticker_read()
{
- uint32_t counter;
-
- TimMasterHandle.Instance = TIM_MST;
-
if (!us_ticker_inited) us_ticker_init();
-#if defined(TARGET_STM32L0)
uint16_t cntH_old, cntH, cntL;
do {
- // For some reason on L0xx series we need to read and clear the
- // overflow flag which give extra time to propelry handle possible
- // hiccup after ~60s
- if (__HAL_TIM_GET_FLAG(&TimMasterHandle, TIM_FLAG_CC1OF) == SET) {
- __HAL_TIM_CLEAR_FLAG(&TimMasterHandle, TIM_FLAG_CC1OF);
- }
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;
}
@@ -79,35 +67,121 @@
} while(cntH_old != cntH);
// Glue the upper and lower part together to get a 32 bit timer
return (uint32_t)(cntH << 16 | cntL);
-#else
- tim_it_update = 0; // Clear TIM_IT_UPDATE event flag
- counter = TIM_MST->CNT + (uint32_t)(SlaveCounter << 16); // Calculate new time stamp
- if (tim_it_update == 1) {
- return tim_it_counter; // In case of TIM_IT_UPDATE return the time stamp that was calculated in timer_irq_handler()
- }
- else {
- return counter; // Otherwise return the time stamp calculated here
- }
-#endif
}
void us_ticker_set_interrupt(timestamp_t timestamp)
{
- int delta = (int)((uint32_t)timestamp - us_ticker_read());
+ // NOTE: This function must be called with interrupts disabled to keep our
+ // timer interrupt setup atomic
+ TimMasterHandle.Instance = TIM_MST;
+ // 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);
- uint16_t cval = TIM_MST->CNT;
+ int current_time = us_ticker_read();
+ int delta = (int)(timestamp - current_time);
if (delta <= 0) { // This event was in the past
- us_ticker_irq_handler();
+ /* Immediately set the compare event to cause the event to be handled in
+ * the next interrupt context. This prevents calling interrupt handlers
+ * recursively as us_ticker_set_interrupt might be called again from the
+ * application handler
+ */
+ oc_int_part = 0;
+ HAL_TIM_GenerateEvent(&TimMasterHandle, TIM_EVENTSOURCE_CC1);
} else {
- oc_int_part = (uint32_t)(delta >> 16);
- oc_rem_part = (uint16_t)(delta & 0xFFFF);
- if (oc_rem_part <= (0xFFFF - cval)) {
- set_compare(cval + oc_rem_part);
- oc_rem_part = 0;
- } else {
- set_compare(0xFFFF);
- oc_rem_part = oc_rem_part - (0xFFFF - cval);
+ /* 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.
+ */
+ oc_int_part = ((uint32_t)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.
+ */
}
}
}
@@ -121,9 +195,7 @@
void us_ticker_clear_interrupt(void)
{
TimMasterHandle.Instance = TIM_MST;
- if (__HAL_TIM_GET_FLAG(&TimMasterHandle, TIM_FLAG_CC1) == SET) {
- __HAL_TIM_CLEAR_FLAG(&TimMasterHandle, TIM_FLAG_CC1);
- }
+ __HAL_TIM_CLEAR_FLAG(&TimMasterHandle, TIM_FLAG_CC1);
}
#endif // TIM_MST_16BIT