Correct/best way to implement a UART-serial passthrough?

RE: Correct/best way to implement a UART-serial passthrough?

Vidar Berg — Mon, 23 Mar 2020 12:29:55 GMT

Sorry, I was missing an 'S' in BLE_GATTS_EVT_HVN_TX_COMPLETE. The event will be reported to all BLE observers/callbacks along with other BLE events such as BLE_GAP_EVT_CONNECTED.

RE: Correct/best way to implement a UART-serial passthrough?

riceman0 — Mon, 23 Mar 2020 12:23:06 GMT

Actually I don't see BLE_GATT_EVT_HVN_TX_COMPLETE defined in the SDK...

RE: Correct/best way to implement a UART-serial passthrough?

riceman0 — Mon, 23 Mar 2020 12:20:21 GMT

Hello, in which handler will the BLE_GATT_EVT_HVN_TX_COMPLETE event occur?

RE: Correct/best way to implement a UART-serial passthrough?

riceman0 — Mon, 23 Mar 2020 10:45:13 GMT

Thanks, I'll give it a shot!

RE: Correct/best way to implement a UART-serial passthrough?

Vidar Berg — Mon, 23 Mar 2020 10:44:20 GMT

Yes that should work as well. I just didn't think of using the event for that.

RE: Correct/best way to implement a UART-serial passthrough?

riceman0 — Mon, 23 Mar 2020 10:40:11 GMT

Pseudocode:

bool sending = false;

[receive data to send]

* put data in buffer

* if not sending, then send next BATCH characters and set sending=true

[BLE_GATT_EVT_HVN_TX_COMPLETE]

* if more data in buffer send next BATCH characters

* else sending = false

Doesn't this take care of everything, variable data, no timers and no termination characters needed?

RE: Correct/best way to implement a UART-serial passthrough?

riceman0 — Mon, 23 Mar 2020 10:29:34 GMT

Oh... well can't this event be used instead of my aforementioned timer, with minimal latency? Every time that fires, if there is more pending data, then send the next batch? You would never need a termination character. Or would that not work for some reason?

RE: Correct/best way to implement a UART-serial passthrough?

Vidar Berg — Mon, 23 Mar 2020 10:26:28 GMT

Sorry, I'm not sure I understand the question. Are you referring to the ble_nus_data_send() function used to send data over BLE? You will get a 'BLE_GATT_EVT_HVN_TX_COMPLETE event when one or more queued notifications has been sent: GATTS Handle Value Notification

RE: Correct/best way to implement a UART-serial passthrough?

riceman0 — Mon, 23 Mar 2020 10:14:01 GMT

I think if there was some sort of event that indicated that a send was *complete* and that the tx is ready to be loaded with new characters would eliminate the need for a timer, and eliminate the latency, wouldn't it? Is there a reason the SDK doesn't provide this?

RE: Correct/best way to implement a UART-serial passthrough?

Vidar Berg — Mon, 23 Mar 2020 10:11:34 GMT

Hi,

The Softdevice can fit 3 notification packets in the output queue by default, so it fills up rather fast if you send small packets instead of buffering the data until it reaches "m_ble_nus_max_data_len". Without any termination characters and with variable packet length I don't see any other option than using a timer as you already suggested. There is a tradeoff between latency and throughput.

1. I made something similar to this a while ago. You may review it here: https://devzone.nordicsemi.com/support-private/support/231178#permalink=476233

2. APP_UART_DATA_READY is triggered per byte that is received.