SD7 send one packet per interval

[jeffdev3]

I am using SD7 and I want to send exactly one 23-byte notification per connection interval.  If I wait for the BLE_GATTS_EVT_HVN_TX_COMPLETE event and call sd_ble_gatts_hvx() then it is sending one notification every other interval.  How do I send one per interval?

[Sigurd]

Hi,

If I wait for the BLE_GATTS_EVT_HVN_TX_COMPLETE event and call sd_ble_gatts_hvx() then it is sending one notification every other interval.

 This makes sense, BLE_GATTS_EVT_HVN_TX_COMPLETE occurs when a notification is acked on the link layer. So this usually requires 2 connection event. First one is for the peripheral to send the packet and the next one is when the packet ACKed by the central. 

How do I send one per interval?

You could use sd_ble_gap_conn_evt_trigger_start , and make it trigger a software interrupt every connection event start. (use the EGU), and in the SW interrupt call sd_ble_gatts_hvx().

[jeffdev3]

Thank you.  I can get it to work using SD7.  Is there a way to do it without using sd_ble_gap_conn_evt_trigger_start()?  I would like to implement it in SD4 which doesn't have this API.

[Sigurd]

An alterative could be to use Radio Notifications:

https://infocenter.nordicsemi.com/topic/sds_s132/SDS/s1xx/radio_notif/radio_notif_peripheral_events.html

https://infocenter.nordicsemi.com/index.jsp?topic=%2Fcom.nordic.infocenter.s132.api.v4.0.2%2Fgroup___n_r_f___s_o_c___f_u_n_c_t_i_o_n_s.html&anchor=gac2dc8aae2c68a2afa1a77340ad59d789

See SDK_folder\components\ble\ble_radio_notification\ble_radio_notification.c for an example on how to use this API.

But note this limitation mentioned in SD release notes: "If Radio Notifications are enabled, flash write and flash erase operations initiated through the SoftDevice API will be notified to the application as Radio Events", so some added sanity testing might need to be added, i.e. check with an timer(RTC-based) how long time it was since last notification was called, and compare that with the connection interval, and/or set a flag before/after you do any flash operations, and ignore events if the flag is set.

Alternatively, a very simple approach would be to just start a RTC timer with a timeout that equals the connection interval, and in the timeout call sd_ble_gatts_hvx(), but without any "sync signal" from the SD, there might be some drift over time, so that at some point, you might perhaps send 0, or 2 notifications in a connection event.