muorb: abs time on aDSP in sync with Linux side

This adds a call on startup of the muorb on the aDSP side to use an
offset for hrt_absolute_call(). This means that the hrt_absolute_call()
on the appsproc (Linux) side should now match the one on the aDSP
(QURT) side.
The accuracy still needs to be determined.

src/platforms/posix/px4_layer/drv_hrt.c

@@ -66,7 +66,11 @@ static void		hrt_call_reschedule(void);
 
 static px4_sem_t 	_hrt_lock;
 static struct work_s	_hrt_work;
+#ifndef __PX4_QURT
 static hrt_abstime px4_timestart = 0;
+#else
+static int32_t dsp_offset = 0;
+#endif
 static hrt_abstime _start_delay_time = 0;
 static hrt_abstime _delay_interval = 0;
 static hrt_abstime max_time = 0;
@@ -150,6 +154,19 @@ hrt_abstime _hrt_absolute_time_internal(void)
 {
 	struct timespec ts;
 
+#if defined(__PX4_QURT)
+	// Don't use the timestart on the DSP on Snapdragon because we manually
+	// set the px4_timestart using the hrt_set_absolute_time_offset().
+	px4_clock_gettime(CLOCK_MONOTONIC, &ts);
+	return ts_to_abstime(&ts) + dsp_offset;
+
+#elif defined(__PX4_POSIX_EAGLE)
+	// Don't do any offseting on the Linux side on the Snapdragon.
+	px4_clock_gettime(CLOCK_MONOTONIC, &ts);
+	return ts_to_abstime(&ts);
+
+#else
+
 	if (!px4_timestart) {
 		px4_clock_gettime(CLOCK_MONOTONIC, &ts);
 		px4_timestart = ts_to_abstime(&ts);
@@ -157,8 +174,17 @@ hrt_abstime _hrt_absolute_time_internal(void)
 
 	px4_clock_gettime(CLOCK_MONOTONIC, &ts);
 	return ts_to_abstime(&ts) - px4_timestart;
+#endif
 }
 
+#ifdef __PX4_QURT
+int hrt_set_absolute_time_offset(int32_t time_diff_us)
+{
+	dsp_offset = time_diff_us;
+	return 0;
+}
+#endif
+
 /*
  * Get absolute time.
  */
@@ -190,7 +216,9 @@ hrt_abstime hrt_absolute_time(void)
 
 __EXPORT hrt_abstime hrt_reset(void)
 {
+#ifndef __PX4_QURT
 	px4_timestart = 0;
+#endif
 	max_time = 0;
 	return _hrt_absolute_time_internal();
 }