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Fix us_ticker for NRF52 series #6796

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Merged
merged 1 commit into from
May 7, 2018
Merged

Fix us_ticker for NRF52 series #6796

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15 changes: 6 additions & 9 deletions targets/TARGET_NORDIC/TARGET_NRF5x/us_ticker.c
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Original file line number Diff line number Diff line change
Expand Up @@ -234,31 +234,28 @@ void common_rtc_set_interrupt(uint32_t us_timestamp, uint32_t cc_channel,
// the interrupt generation.
uint64_t current_time64 = common_rtc_64bit_us_get();
// [add upper 32 bits from the current time to the timestamp value]
uint64_t timestamp64 = us_timestamp +
(current_time64 & ~(uint64_t)0xFFFFFFFF);
uint64_t timestamp64 = (current_time64 & ~(uint64_t)0xFFFFFFFF) | us_timestamp;
// [if the original timestamp value happens to be after the 32 bit counter
// of microsends overflows, correct the upper 32 bits accordingly]
if (us_timestamp < (uint32_t)(current_time64 & 0xFFFFFFFF)) {
if (timestamp64 < current_time64) {
timestamp64 += ((uint64_t)1 << 32);
}
// [microseconds -> ticks, always round the result up to avoid too early
// interrupt generation]
uint32_t compare_value =
(uint32_t)CEIL_DIV((timestamp64) * RTC_INPUT_FREQ, 1000000);

uint32_t compare_value = RTC_WRAP((uint32_t)CEIL_DIV((timestamp64) * RTC_INPUT_FREQ, 1000000));

core_util_critical_section_enter();
// The COMPARE event occurs when the value in compare register is N and
// the counter value changes from N-1 to N. Therefore, the minimal safe
// difference between the compare value to be set and the current counter
// value is 2 ticks. This guarantees that the compare trigger is properly
// setup before the compare condition occurs.
uint32_t closest_safe_compare = common_rtc_32bit_ticks_get() + 2;
if ((int)(compare_value - closest_safe_compare) <= 0) {
uint32_t closest_safe_compare = RTC_WRAP(common_rtc_32bit_ticks_get() + 2);
if (closest_safe_compare - compare_value < 2) {
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I might have missed something, but if compare_value is equal to the current RTC ticks value, that is compare_value == common_rtc_32bit_ticks_get(), this condition will be false and an invalid value will be written to CC register. Was that intentional? That new condition might well be replaced with: if (compare_value + 1 == closest_safe_compare).

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I think you are right. It should have been <= 2 in the comparison. However, the new 5.9 tickers are about to land so I don't think we should fix this.

compare_value = closest_safe_compare;
}

nrf_rtc_cc_set(COMMON_RTC_INSTANCE, cc_channel, RTC_WRAP(compare_value));
nrf_rtc_cc_set(COMMON_RTC_INSTANCE, cc_channel, compare_value);
nrf_rtc_event_enable(COMMON_RTC_INSTANCE, int_mask);

core_util_critical_section_exit();
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