BLE NUS service

RE: BLE NUS service

Vidar Berg — Mon, 30 Mar 2020 07:55:09 GMT

Good to hear that it works now.

[quote user="jedmvpitech"]Now to figure out how to reset the iOS device (not really a fan of it).[/quote]

Reboot/restart the iPad, not reset it.

RE: BLE NUS service

Jed Marti — Sat, 28 Mar 2020 18:44:13 GMT

Tried it with another device and yes that's the problem. Dave P. and I fiddled with this for hours. Now to figure out how to reset the iOS device (not really a fan of it).

RE: BLE NUS service

Vidar Berg — Sat, 28 Mar 2020 15:52:22 GMT

It is writing to the wrong handle, and it's likely related to attribute caching. Attribute caching is a feature defined by the BT spec. that allows GATT clients to store the attribute table (i.e. layout of services and characteristics) of "known" device across connections, and thus removing the overhead of having to repeat service discovery on subsequent connections. You may take a look at core spec 5. vol3, part g, section 2.5.2 for more details. It gives a good summary of the feature and how it's used.

The problem with caching arises when the same device is updated with a different attribute table and thus invalidates the existing cache on the client side. It isn't uncommon for this to happen during development and having the client accessing the wrong characteristics as a result. The solution for this is to make a new service discovery. iOS does not expose an API, so it's not possible to do programmatically, but you can force rediscovery by clearing the cache. The cache can be removed by first making sure your device is not in the "MY DEVICES" list in Bluetooth settings, followed by a reboot. Please try either that or try connecting with another device.

RE: BLE NUS service

Jed Marti — Sat, 28 Mar 2020 13:52:05 GMT

I'm using Light Blue as the client on an iPAD and just sending random values for the first two bytes.Sending only two bytes of /r/n or \n\r gets its attention but I only get STOP and START events. I'm using read/write characteristic 1. I'm unable to get nRFconnect to behave - when I try to send messages it just blinks the message text and doesn't do anything.

RE: BLE NUS service

Vidar Berg — Sat, 28 Mar 2020 06:43:10 GMT

Hello,

It looks like your GATT client is using the wrong attribute handle for some reason. It should only access the 2 byte CCCD handle when it wants to enable or disable notifications on the NUS TX characteristic. To generate the BLE_NUS_EVT_RX_DATA event it needs write to the p_nus->rx_handles.value_handle. Is your client doing service discovery on connection, or does it rely on existing hardcoded attribute handles?

Note that you can test the Service with our nRF connect app on Android or iOS as well.