NRF52: fix us_ticker IRQ handler

Applying PR to NRF52 SDK 14.2:
#5046

Author: Marcus Chang

targets/TARGET_NORDIC/TARGET_NRF5x/common_rtc.h

@@ -33,6 +33,9 @@
 #define OS_TICK_CC_CHANNEL      1
 #define LP_TICKER_CC_CHANNEL    2
 
+#define US_TICKER_SW_IRQ_MASK 0x1
+#define LP_TICKER_SW_IRQ_MASK 0x2
+
 #define COMMON_RTC_EVENT_COMPARE(channel) \
     CONCAT_2(NRF_RTC_EVENT_COMPARE_, channel)
 #define COMMON_RTC_INT_COMPARE_MASK(channel) \
@@ -47,6 +50,7 @@
 
 extern bool              m_common_rtc_enabled;
 extern uint32_t volatile m_common_rtc_overflows;
+extern uint8_t volatile m_common_sw_irq_flag; 
 
 void     common_rtc_init(void);
 uint32_t common_rtc_32bit_ticks_get(void);

targets/TARGET_NORDIC/TARGET_NRF5x/lp_ticker.c

@@ -18,6 +18,7 @@
 #if DEVICE_LOWPOWERTIMER
 
 #include "common_rtc.h"
+#include "mbed_critical.h"
 
 void lp_ticker_init(void)
 {
@@ -37,10 +38,10 @@ void lp_ticker_set_interrupt(timestamp_t timestamp)
 
 void lp_ticker_fire_interrupt(void)
 {
-    uint32_t closest_safe_compare = common_rtc_32bit_ticks_get() + 2;
-
-    nrf_rtc_cc_set(COMMON_RTC_INSTANCE, LP_TICKER_CC_CHANNEL, RTC_WRAP(closest_safe_compare));
-    nrf_rtc_event_enable(COMMON_RTC_INSTANCE, LP_TICKER_INT_MASK);
+    core_util_critical_section_enter();
+    m_common_sw_irq_flag |= LP_TICKER_SW_IRQ_MASK;
+    NVIC_SetPendingIRQ(RTC1_IRQn);
+    core_util_critical_section_exit();
 }
 
 void lp_ticker_disable_interrupt(void)

targets/TARGET_NORDIC/TARGET_NRF5x/us_ticker.c

@@ -43,12 +43,14 @@
 #include "lp_ticker_api.h"
 #include "mbed_critical.h"
 
+#if defined(NRF52_ERRATA_20)
 #if defined(SOFTDEVICE_PRESENT)
 #include "nrf_sdh.h"
 #define NRF_HAL_US_TICKER_SD_IS_ENABLED() nrf_sdh_is_enabled()
 #else
 #define NRF_HAL_US_TICKER_SD_IS_ENABLED() 0
 #endif
+#endif
 
 //------------------------------------------------------------------------------
 // Common stuff used also by lp_ticker and rtc_api (see "common_rtc.h").
@@ -58,6 +60,9 @@
 bool              m_common_rtc_enabled = false;
 uint32_t volatile m_common_rtc_overflows = 0;
 
+// lp/us ticker fire interrupt flag for IRQ handler
+volatile uint8_t m_common_sw_irq_flag = 0;
+
 __STATIC_INLINE void rtc_ovf_event_check(void)
 {
     if (nrf_rtc_event_pending(COMMON_RTC_INSTANCE, NRF_RTC_EVENT_OVERFLOW)) {
@@ -77,11 +82,15 @@ void COMMON_RTC_IRQ_HANDLER(void)
 
     rtc_ovf_event_check();
 
-    if (nrf_rtc_event_pending(COMMON_RTC_INSTANCE, US_TICKER_EVENT)) {
+    if ((m_common_sw_irq_flag & US_TICKER_SW_IRQ_MASK) || nrf_rtc_event_pending(COMMON_RTC_INSTANCE, US_TICKER_EVENT)) {
         us_ticker_irq_handler();
     }
 
 #if DEVICE_LOWPOWERTIMER
+    if (m_common_sw_irq_flag & LP_TICKER_SW_IRQ_MASK) {
+        m_common_sw_irq_flag &= ~LP_TICKER_SW_IRQ_MASK;
+        lp_ticker_irq_handler();
+    }
     if (nrf_rtc_event_pending(COMMON_RTC_INSTANCE, LP_TICKER_EVENT)) {
 
         lp_ticker_irq_handler();
@@ -117,7 +126,7 @@ void common_rtc_init(void)
     errata_20();
 
     NVIC_SetVector(RTC1_IRQn, (uint32_t)RTC1_IRQHandler);
-    
+
     // RTC is driven by the low frequency (32.768 kHz) clock, a proper request
     // must be made to have it running.
     // Currently this clock is started in 'SystemInit' (see "system_nrf51.c"
@@ -276,10 +285,10 @@ void us_ticker_set_interrupt(timestamp_t timestamp)
 
 void us_ticker_fire_interrupt(void)
 {
-    uint32_t closest_safe_compare = common_rtc_32bit_ticks_get() + 2;
-
-    nrf_rtc_cc_set(COMMON_RTC_INSTANCE, US_TICKER_CC_CHANNEL, RTC_WRAP(closest_safe_compare));
-    nrf_rtc_event_enable(COMMON_RTC_INSTANCE, US_TICKER_INT_MASK);
+    core_util_critical_section_enter();
+    m_common_sw_irq_flag |= US_TICKER_SW_IRQ_MASK;
+    NVIC_SetPendingIRQ(RTC1_IRQn);
+    core_util_critical_section_exit();
 }
 
 void us_ticker_disable_interrupt(void)
@@ -289,6 +298,7 @@ void us_ticker_disable_interrupt(void)
 
 void us_ticker_clear_interrupt(void)
 {
+    m_common_sw_irq_flag &= ~US_TICKER_SW_IRQ_MASK;
     nrf_rtc_event_clear(COMMON_RTC_INSTANCE, US_TICKER_EVENT);
 }