Central GATT write ignored on Raspberry Pi

[Gordon]

Hi,

I've been trying to get an implementation of the HTTP Proxy working with nRF52. The nRF52 is in central mode, accessing the proxy (running on a Pi with Bleno) which is exposing some characteristics.

I can access the proxy using the nRF connect app just fine, can read and write characteristics, and everything works great.

I can also connect with the nRF52 now (thanks!), I can list services and characteristics, and I can read characteristics. However: when I write to a characteristic the command succeeds and I get a BLE_EVT_TX_COMPLETE event, but the Raspberry Pi doesn't register the write at all (for single byte or multibyte characteristics).

However it works perfectly when writing characteristics on another nRF52.

Any thoughts on what the problem could be here? I'm using sd_ble_gattc_write with BLE_GATT_OP_WRITE_CMD and BLE_GATT_EXEC_WRITE_FLAG_PREPARED_WRITE.

On the multibyte characteristic it can also fail with a DATA_SIZE error if the string is too long - but the nRF connect app doesn't. Is there some other type of write command that I'm missing, or does it need to send another write with a special offset to 'end' the transmission?

[Gordon]

Just to add, I was writing to p_chr->handle_value - but I notice that discovery db gets used and then cccd_handle is passed is most cases. Is it a problem that this appears to work when writing to another nRF52?

[Petter Myhre]

I'm having trouble understand what you mean in your comment, but you could try to send a write request instead of a write command, and then check the BLE_GATTC_EVT_WRITE_RSP event? See this MSC for more information.

[Gordon]

I've been using handle_value from the BLE_GATTC_EVT_CHAR_DISC_RSP event to write to, but looking at examples, cccd_handle seems to be used, which comes from BLE_GATTC_EVT_DESC_DISC_RSP. So I guess potentially that could be an issue. I'll try a write request though - should that work with all types of peer?

[Petter Myhre]

Depends on what you want to write to, if you want to write to the characteristic value you should use the handle of the characteristic value, if you want to write to the CCCD you should use the CCCD handle.

Both types should work as long as the attribute you are writing to can be written to, and doesn't require authorization, authentication or encryption.

[Gordon]

Thanks! Just tried this and it worked - maybe it's a bug in noble, but it looks like BLE_GATT_OP_WRITE_CMD gets ignored but BLE_GATTC_EVT_WRITE_RSP works.