Time synchronization with alternating masters

[EgbertK]

Dear members,

with success I implemented the time synchronization example from the nRF5 SDK guide.
This example works perfect for a single master, but what if the master changes?
When I check my scope it will show that the new master starts sending the sync beacons, but the slave (previous master) is not receiving and stays low.
Would there be a solution to put a master in receiver mode after stopping the sync beacons?

I am using four nRF52840-DKs with Segger Studio, SDK 17 and a S140 softdevice (used for a custom BLE service)

[Kenneth]

Hello,

The example is not an official release, but I can try to ping the person that made the example if he can take a look. He is currently out of office until after Easter though.

Kenneth

[EgbertK]

Hello Kenneth,

that would be great. If I find the solution before Easter I will let you know ;).

Regards, Egbert

[EgbertK]

Hello Kenneth,

I was not able to find a solution to this item. Did you managed to contact the creator of this example?

Regards, Egbert

[Audun]

Hi Egbert,

I suspect there is state information still lingering after stopping the transmitter. Could you try the attached diff on your side?

My test was  the following, based on 2 x nRF52-DK.

1) Press button 1 on DK #1 to assign this role of transmitter

2) Observe that both DKs toggle GPIO in unison

3) Press button 1 on DK #1 to stop transmitting

4) Wait until DK #2 reports desynchronization (GPIO stops togglnig)

5) Press button 1 on DK #2 to assign this role of transmitter

6) Observe that both DKs toggle GPIO in unison

Fullscreen stop.diff Download

diff --git a/nRF5_SDK_16.0.0_98a08e2/examples/common/time_sync.c b/nRF5_SDK_16.0.0_98a08e2/examples/common/time_sync.c
index 4a21351..871498a 100644
--- a/nRF5_SDK_16.0.0_98a08e2/examples/common/time_sync.c
+++ b/nRF5_SDK_16.0.0_98a08e2/examples/common/time_sync.c
@@ -128,6 +128,7 @@ static nrf_atomic_u32_t m_sync_pkt_ringbuf_idx;
 
 static nrf_atomic_flag_t m_timeslot_session_open;
 static nrf_atomic_flag_t m_pending_close;
+static nrf_atomic_flag_t m_pending_tx_stop;
 static nrf_atomic_u32_t  m_blocked_cancelled_count;
 static uint32_t          m_total_timeslot_length = 0;
 static uint32_t          m_timeslot_distance = 0;
@@ -469,6 +470,15 @@ void timeslot_begin_handler(void)
 
     m_total_timeslot_length = 0;
 
+    if (m_pending_tx_stop)
+    {
+        nrf_atomic_flag_clear(&m_send_sync_pkt);
+        nrf_atomic_flag_clear(&m_pending_tx_stop);
+        m_timeslot_distance = 0;
+        m_synchronized = false;
+        m_master_counter_diff = 0;
+    }
+
     if (!m_send_sync_pkt)
     {
         if (m_radio_state    != RADIO_STATE_RX ||
@@ -737,6 +747,7 @@ void SWI3_EGU3_IRQHandler(void)
         if (m_synchronized)
         {
             m_synchronized = false;
+            m_master_counter_diff = 0;
 
             if (m_callback)
             {
@@ -1217,7 +1228,7 @@ uint32_t ts_tx_start(uint32_t sync_freq_hz)
 
 uint32_t ts_tx_stop()
 {
-    nrf_atomic_flag_clear(&m_send_sync_pkt);
+    nrf_atomic_flag_set(&m_pending_tx_stop);
 
     return NRF_SUCCESS;
 }

Best regards,

Audun

[Audun]

Hi again,

I thought about it some more and decided the previous diff was a not so good workaround. This one should work better, as it doesn't reset the "m_master_counter_diff" variable. Resetting this variable would cause a jump in timestamps, which is probably not desirable.

Best regards,

Audun

Fullscreen 5164.stop.diff Download

diff --git a/nRF5_SDK_16.0.0_98a08e2/examples/common/time_sync.c b/nRF5_SDK_16.0.0_98a08e2/examples/common/time_sync.c
index 4a21351..65c5c13 100644
--- a/nRF5_SDK_16.0.0_98a08e2/examples/common/time_sync.c
+++ b/nRF5_SDK_16.0.0_98a08e2/examples/common/time_sync.c
@@ -128,6 +128,7 @@ static nrf_atomic_u32_t m_sync_pkt_ringbuf_idx;
 
 static nrf_atomic_flag_t m_timeslot_session_open;
 static nrf_atomic_flag_t m_pending_close;
+static nrf_atomic_flag_t m_pending_tx_stop;
 static nrf_atomic_u32_t  m_blocked_cancelled_count;
 static uint32_t          m_total_timeslot_length = 0;
 static uint32_t          m_timeslot_distance = 0;
@@ -469,6 +470,14 @@ void timeslot_begin_handler(void)
 
     m_total_timeslot_length = 0;
 
+    if (m_pending_tx_stop)
+    {
+        nrf_atomic_flag_clear(&m_send_sync_pkt);
+        nrf_atomic_flag_clear(&m_pending_tx_stop);
+        m_timeslot_distance = 0;
+        m_synchronized = false;
+    }
+
     if (!m_send_sync_pkt)
     {
         if (m_radio_state    != RADIO_STATE_RX ||
@@ -517,6 +526,7 @@ void timeslot_begin_handler(void)
 
     p_pkt->timer_val   = m_params.high_freq_timer[0]->CC[1];
     p_pkt->counter_val = m_params.high_freq_timer[1]->CC[1];
+    p_pkt->counter_val += m_master_counter_diff;
 
 //    p_pkt->rtc_val     = m_params.rtc->COUNTER;
 
@@ -1217,7 +1227,7 @@ uint32_t ts_tx_start(uint32_t sync_freq_hz)
 
 uint32_t ts_tx_stop()
 {
-    nrf_atomic_flag_clear(&m_send_sync_pkt);
+    nrf_atomic_flag_set(&m_pending_tx_stop);
 
     return NRF_SUCCESS;
 }