debugging sd_ble_gatts_hvx

[wim]

Hi

I am trying to get to the bottom of a problem I am having with sending a buffer of data on connection and indication enable. Here's what I do: I have a process running, which is capturing sensor data every 10 seconds, and keeping it in a circular buffer. When a master connects, I want to send the circular buffer to the master app. I am doing that by triggering on the event that the CCCD is written to enable indications (I am using indication because I want to make sure that the values end up in the app). When this CCCD write is happening, I send the first item in my circular buffer, and then use the BLE_GATTS_EVT_HVC event to see if I have gotten a confirmation, just as in the health thermometer example.

I am running into a number of problems

• when I trigger on the CCCD write and immediately do a sd_ble_gatts_hvx, I get an error 8 (illegal state); if I start a timer and do the same after 10 ms, then it is ok
• I sometimes also have a BLE_ERROR_GATTS_SYS_ATTR_MISSING error, how can I avoid that? when should I normally do a sd_ble_gatts_sys_attr_set(m_conn_handle, NULL, 0) (i do not use bonding)

I have the impression that timing issues or race conditions are causing my problems, can anyone give me hint on how to solve this?

[Carles]

Reading your last comment, and as Ulrich says, here's a list of possible causes to your issue:

1. You may be waiting for the wrong CCCD write. Double-check that your CCCD handle matches the one you got when you added the characteristic
2. You may be calling hvx() with the wrong characteristic value handle. Remember that this has to be the characteristic value handle and not a CCCD or any other handle.
3. You may be calling hvx() twice with the right handle. The HVC event will take a while to come back and so you need to exit your event processing loop while waiting for it.

If none of this helps you could always send us a PM with your code and we can take a look at it.