Disable TX notifications

[Simon]

Hello,

the peripheral (nRF52) bonds to a central (Android nRF Connect), central enables TX notifications, and the peripheral sends over 80 bytes by NUS.

If the central does not disable TX notifications and lets disconnect occur, and because the devices were bonded, TX notification on the central will already be enabled on the next connection. If the peripheral tries another ble_nus_data_send() a NRF_ERROR_INVALID_STATE is returned. (Not looking to have the peripheral send data automatically on subsequent connections).

Is the standard procedure to have the central disable TX notifications before disconnecting, or for the peripheral upon reaching BLE_GATTS_HVN_TX_COMPLETE to some way disable TX notifications, or some way let the central know that there is no more?

thank-you,

[Simonr]

Hi

Correct, the central will remember the settings of a paired connection and "automagically" keep the same settings for the next time the peripheral connects, so you will have to disable the TX notifications when you disconnect if you don't want to have notifications enabled upon the next connections. When disabling the notifications, the queue will be emptied before the transmissions are stopped, however the application won't be able to place new notifications in the queue after notifications are disabled by the peer.

Typically, notifications are enabled on the initial connection, and then enabled for the remainder of the devices life time. This allows the peripheral to send notifications as it sees fit to the central device. If you want to control the amount of data received on the central device, it's more common to add a characteristic that the central can write commands to. This may be a command to tell the peripheral device to send X amount of notifications and then stop.

If you enable and disable notifications dynamically, you'll quickly end up in race conditions between buffering of notifications on lower levels in the stack.

Best regards,

Simon

[Simon]

Other than the central managing start/stop,
are any options are available for the peripheral to tell the central that there is no more data to send and that it is ok to disable TX notifications?

thank-you,

[Simonr]

Hi

No, not that I'm aware of at least. If you always transmit the same amount of data from the peripheral, I guess you could make the central disable notifications once you have received X amount of data, but this won't do if the peripheral doesn't send the same amount of during every connection.

Best regards,

Simon

[Simon]

I added an additional send() to the trailing notification to only have 0xFFFFFFFF to signal the central that its ok to disable TX notification. Maybe central is ok with this.

thank-you,