Restored alternative method of RTOS tick generation for NRF51, which was undesirably removed when the new us_ticker implementation was introduced.

Author: anangl

hal/targets/hal/TARGET_NORDIC/TARGET_NRF5/TARGET_MCU_NRF51822/sdk/nrf_drv_config.h

@@ -138,7 +138,7 @@
 #define RTC0_INSTANCE_INDEX      0
 #endif
 
-#define RTC1_ENABLED 1
+#define RTC1_ENABLED 0
 
 #if (RTC1_ENABLED == 1)
 #define RTC1_CONFIG_FREQUENCY    32768

hal/targets/hal/TARGET_NORDIC/TARGET_NRF5/TARGET_MCU_NRF52832/sdk/nrf_drv_config.h

@@ -138,7 +138,7 @@
 #define RTC0_INSTANCE_INDEX      0
 #endif
 
-#define RTC1_ENABLED 1
+#define RTC1_ENABLED 0
 
 #if (RTC1_ENABLED == 1)
 #define RTC1_CONFIG_FREQUENCY    32768

hal/targets/hal/TARGET_NORDIC/TARGET_NRF5/rtc_common.h renamed to hal/targets/hal/TARGET_NORDIC/TARGET_NRF5/common_rtc.h

@@ -14,21 +14,26 @@
  * limitations under the License.
  */
 
-#ifndef RTC_COMMON_H
-#define RTC_COMMON_H
+#ifndef COMMON_RTC_H
+#define COMMON_RTC_H
 
-#include "nrf_drv_rtc.h"
+#include "nrf_rtc.h"
 
-#define RTC_COUNTER_BITS        24
+#define RTC_COUNTER_BITS        24u
 
-#define LP_TICKER_CC_CHANNEL    0
-#define US_TICKER_CC_CHANNEL    1
+// Instance 0 is reserved for SoftDevice.
+// Instance 1 is used as a common one for us_ticker, lp_ticker and (in case
+// of NRF51) as an alternative tick source for RTOS.
+#define COMMON_RTC_INSTANCE     NRF_RTC1
 
-extern nrf_drv_rtc_t const m_rtc_common;
-extern bool                m_rtc_common_enabled;
-extern uint32_t volatile   m_rtc_common_overflows;
+#define US_TICKER_CC_CHANNEL    0
+#define OS_TICK_CC_CHANNEL      1
+#define LP_TICKER_CC_CHANNEL    2
 
-void     rtc_common_init(void);
-uint32_t rtc_common_32bit_ticks_get(void);
+extern bool              m_common_rtc_enabled;
+extern uint32_t volatile m_common_rtc_overflows;
 
-#endif // RTC_COMMON_H
+void     common_rtc_init(void);
+uint32_t common_rtc_32bit_ticks_get(void);
+
+#endif // COMMON_RTC_H

hal/targets/hal/TARGET_NORDIC/TARGET_NRF5/lp_ticker.c

@@ -17,42 +17,37 @@
 
 #if DEVICE_LOWPOWERTIMER
 
-#include "rtc_common.h"
+#include "common_rtc.h"
 #include "sleep_api.h"
 
 void lp_ticker_init(void)
 {
-    rtc_common_init();
+    common_rtc_init();
 }
 
 uint32_t lp_ticker_read(void)
 {
-    return rtc_common_32bit_ticks_get();
+    return common_rtc_32bit_ticks_get();
 }
 
 void lp_ticker_set_interrupt(uint32_t now, uint32_t time)
 {
     (void)now;
-    // The passed 32-bit 'time' value is wrapped properly by the driver, so it
-    // is usable by the 24-bit counter.
-    ret_code_t result = nrf_drv_rtc_cc_set(&m_rtc_common, LP_TICKER_CC_CHANNEL,
-        time, true);
-    if (result != NRF_SUCCESS)
-    {
-        MBED_ASSERT(false);
-    }
+    nrf_rtc_cc_set(COMMON_RTC_INSTANCE, LP_TICKER_CC_CHANNEL, RTC_WRAP(time));
+    nrf_rtc_event_clear(COMMON_RTC_INSTANCE, NRF_RTC_EVENT_COMPARE_2);
+    nrf_rtc_event_enable(COMMON_RTC_INSTANCE, NRF_RTC_INT_COMPARE2_MASK);
 }
 
 uint32_t lp_ticker_get_overflows_counter(void)
 {
-    // Cut out the part of 'm_rtc_common_overflows' used by
-    // 'rtc_common_32bit_ticks_get()'.
-    return (m_rtc_common_overflows >> (32 - RTC_COUNTER_BITS));
+    // Cut out the part of 'm_common_rtc_overflows' used by
+    // 'common_rtc_32bit_ticks_get()'.
+    return (m_common_rtc_overflows >> (32u - RTC_COUNTER_BITS));
 }
 
 uint32_t lp_ticker_get_compare_match(void)
 {
-    return nrf_rtc_cc_get(m_rtc_common.p_reg, LP_TICKER_CC_CHANNEL);
+    return nrf_rtc_cc_get(COMMON_RTC_INSTANCE, LP_TICKER_CC_CHANNEL);
 }
 
 void lp_ticker_sleep_until(uint32_t now, uint32_t time)