Nimble: Reduce BLE power usage

This configures Nimble to enable the HFCLOCK and other
Bluetooth peripherals only when needed, but 1500 us in advance.
This time is recommended by the Mynewt docs.

src/CMakeLists.txt

@@ -780,6 +780,7 @@ add_definitions(-DNRF52 -DNRF52832 -DNRF52832_XXAA -DNRF52_PAN_74 -DNRF52_PAN_64
 add_definitions(-DFREERTOS)
 add_definitions(-D__STACK_SIZE=1024)
 add_definitions(-D__HEAP_SIZE=4096)
+add_definitions(-DMYNEWT_VAL_BLE_LL_RFMGMT_ENABLE_TIME=1500)
 
 # Note: Only use this for debugging
 # Derive the low frequency clock from the main clock (SYNT)

src/libs/mynewt-nimble/porting/npl/freertos/include/nimble/nimble_npl_os.h

@@ -37,6 +37,8 @@ extern "C" {
 
 #define BLE_NPL_TIME_FOREVER    portMAX_DELAY
 
+extern volatile int ble_npl_in_critical;
+
 /* This should be compatible with TickType_t */
 typedef uint32_t ble_npl_time_t;
 typedef int32_t ble_npl_stime_t;
@@ -282,14 +284,22 @@ static inline uint32_t
 ble_npl_hw_enter_critical(void)
 {
     //vPortEnterCritical();
+    ++ble_npl_in_critical;
     return npl_freertos_hw_enter_critical();
 }
 
 static inline void
 ble_npl_hw_exit_critical(uint32_t ctx)
 {
+    --ble_npl_in_critical;
     npl_freertos_hw_exit_critical(ctx);
+}
 
+static inline bool
+ble_npl_hw_is_in_critical(void)
+{
+    // Do the same as RIOT and keep track of the critical state manually
+    return (ble_npl_in_critical > 0);
 }
 
 #ifdef __cplusplus

src/libs/mynewt-nimble/porting/npl/freertos/src/npl_os_freertos.c

@@ -22,6 +22,8 @@
 #include <string.h>
 #include "nimble/nimble_npl.h"
 
+volatile int ble_npl_in_critical = 0;
+
 static inline bool
 in_isr(void)
 {