bt_nus_client_send failed (err -120) happend in certain frequency

[Ziyao Zhou]

Hi,

I have twp device: one peripheral and one central. My peripheral is sending out high payload data continiously. And my central is sending data ()in 10Hz frequency. However, every few times  I 'll receive bt_nus_client_send failed (err -120). I noticed that 120 means Operation already in progress. How to solve this issue? Or the central can only sending data very slow.

Whether it is relative to my setting interval=320 (400 ms), latency=0, timeout=400

Thank you for your help!

	 err = bt_nus_client_send(&nus_client, nus_data.data, nus_data.len);
				 if (err) {
					 LOG_WRN("Failed to send data over BLE connection"
						 "(err %d)", err);
				 }
 

[Kenneth]

Hello,

If you want to send data every 100ms, I think it also make most sense to set the interval to 100ms. Else you will get very prone to interference and packet loss, since you will depend having to send multiple packets every interval.

If you experience operation in progress error, you can simply go to sleep and wait until for instance next connection interval and try again.

Kenneth

[Ziyao Zhou]

Hi,

Thank you for your information. I am using bt_nus_send sending out data from peripheral to central without stop and there is no error sign. However, some time when I use bt_nus_client_send sending from central to peripheral  I will got the error sign. As two ends are using same interval, why only in central side will I receive this error?

[Kenneth]

There are two different api's used here: bt_gatt_notify() vs. bt_gatt_write(). First is used from server->client and second client->server.

EBUSY (-16): Indicates that the operation cannot proceed because the Bluetooth stack is busy with another transaction. This can happen if a previous GATT write is still in progress or if another BLE procedure is ongoing that prevents new writes.

Kenneth

[Ziyao Zhou]

Thank you for your information! That means my bt_nus_send is blocking bt_nus_client_send? 

However, when I delete "bt_nus_send " in my peripheral and do the experiment again I still got a lot of error 120 (not EBUSY (-16) you mentioned)

[Kenneth]

I would not expect that removing bt_nus_send() would help no, the bt_nus_client_send() is blocking itself sometimes. Please reduce connection interval if you want to improve.

Kenneth

[Ziyao Zhou]

I think I have figure out, if I change to bt_gatt_write_without_response 

thanks a lot

[Kenneth]

Good point, didn't think of that, glad you found a workaround.

[Ziyao Zhou]

Hi

I still got one question, I notice that when I reduce the connection interval, some time I cannot send out in central device. Is bt_nus_send and bt_nus_client_send  happening together in one connection interval?

[Kenneth]

Hi,

In BLE there will always be packets going both ways, either empty packets or packets with useful data for the application. Data is only sent at each connection event, which happens at each connection interval. This means that if you have written several packets between interval, the packets will be sent one after the other, with a bidirectional packet between each packet. Also not that if there is any interference or noise occurring that cause the CRC to fail, then it will immediately stop communication that connection event, and retry on next connection interval.

Kenneth