implement delay_ns with DWT

Author: hathach

cores/nRF5/delay.c

@@ -40,6 +40,20 @@ void delay( uint32_t ms )
   vTaskDelay(ms2tick(ms));
 }
 
+void dwt_enable(void)
+{
+  CoreDebug->DEMCR |= CoreDebug_DEMCR_TRCENA_Msk; /* Global Enable for DWT */
+  DWT->CYCCNT = 0;                                /* Reset the counter */
+  DWT->CTRL |= DWT_CTRL_CYCCNTENA_Msk;            /* Enable cycle counter */
+}
+
+void dwt_disable(void)
+{
+  DWT->CTRL &= ~DWT_CTRL_CYCCNTENA_Msk;
+  CoreDebug->DEMCR &= ~CoreDebug_DEMCR_TRCENA_Msk;
+}
+
+
 #ifdef __cplusplus
 }
 #endif

cores/nRF5/delay.h

@@ -56,7 +56,7 @@ extern uint32_t micros( void ) ;
  *
  * \param dwMs the number of milliseconds to pause (uint32_t)
  */
-extern void delay( uint32_t dwMs ) ;
+extern void delay( uint32_t dwMs );
 
 /**
  * \brief Pauses the program for the amount of time (in microseconds) specified as parameter.
@@ -74,6 +74,34 @@ static __inline__ void delayMicroseconds( uint32_t usec )
   nrf_delay_us(usec);
 }
 
+void dwt_enable(void);
+void dwt_disable(void);
+
+
+/**
+ * Delay nano seconds, delay_ns() make use of DWT of debug core.
+ * dwt_enable() must be called previously.
+ * Note: nrf52 run at 64MHz
+ *    - 1000 ns ~ 64 cycles
+ *    -  500 ns ~ 32 cycles
+ *    -  250 ns ~ 16 cycles
+ *    -  125 ns ~  8 cycles
+ */
+// Enable pragma when this bug is fixed  https://bugs.launchpad.net/gcc-arm-embedded/+bug/1534360
+// #pragma GCC push_options
+// #pragma GCC optimize ("Ofast")
+
+#define DELAY_CYCLE_CORRECTION   8 // ~125 ns overhead for delay_ns()
+#define delay_ns(ns) \
+  do {\
+    register uint32_t _endtime = DWT->CYCCNT;\
+    _endtime += ((F_CPU/1000000)*ns)/1000 - DELAY_CYCLE_CORRECTION;\
+    while (DWT->CYCCNT < _endtime) {}\
+  } while(0)
+
+// #pragma GCC pop_options
+
+
 #ifdef __cplusplus
 }
 #endif

cores/nRF5/nrf52_flash.c

@@ -40,6 +40,7 @@
 #if CFG_DEBUG
 #define CFG_DEBUG_NFFS  0
 
+#if CFG_DEBUG_NFFS
 static void print_buf(const uint8_t* address, uint32_t count)
 {
   for(uint32_t i=0; i<count; i++) cprintf("%02X ", address[i] );
@@ -66,6 +67,8 @@ static void print_write_after(uint32_t address, uint32_t count)
 }
 #endif
 
+#endif
+
 static SemaphoreHandle_t _evt_sem = NULL;
 static volatile uint32_t _op_result;