Data length update not correct.

RE: Data length update not correct.

T IJ — Wed, 31 Jul 2024 12:06:54 GMT

Thank you for the example, I will investigate this and come back to this ticket when I have some more information

RE: Data length update not correct.

Simonr — Tue, 30 Jul 2024 08:59:38 GMT

In the nRF5 SDK, the best way to transfer big chunks of data is to split it into 244. The object transfer service example might be useful for reference: https://infocenter.nordicsemi.com/index.jsp?topic=%2Fcom.nordic.infocenter.sdk5.v15.3.0%2Fble_sdk_app_ots.html

Best regards,

Simon

RE: Data length update not correct.

T IJ — Mon, 29 Jul 2024 11:10:19 GMT

devzone.nordicsemi.com/.../capture-0.pcapng
I have a capture done with the negotiation, maybe you can get more information from this.

I will try to set the MTU to 247, the problem is that we probably want to send more data than the 244 bytes possible.
Could this be an issue?

RE: Data length update not correct.

Simonr — Mon, 29 Jul 2024 06:29:54 GMT

Most devices don't accept Attribute data sizes larger than 244 I'm afraid, so setting the NRF_SDH_BLE_GATT_MAX_MTU_SIZE to 247 will make room for the 3 byte ATT header and also allow you to send the 244 bytes of attribute data.

Depending on the BLE stack on your PC, it could also be the case that it only supports up to 27 bytes of attribute data. What data length negotiation issues are you seeing exactly?

Best regards,

Simon

RE: Data length update not correct.

T IJ — Thu, 25 Jul 2024 13:25:19 GMT

I am not using extended advertising and my connection interval is set to 10ms.

I'm not interested in fine tuning the throughput, I already have done this using two development kits.

The problem I'm facing is that I want to have the same connection between my Windows PC instead of using a development kit I get issues with negotiating the data length.

In the SDK config I have #define NRF_SDH_BLE_GAP_DATA_LENGTH 251 and #define NRF_SDH_BLE_GATT_MAX_MTU_SIZE 500

This works perfectly when communicating between two development kits since they both accept the data length and the time to send/receive but not when I connect the same board to my PC.

RE: Data length update not correct.

Simonr — Thu, 25 Jul 2024 12:57:58 GMT

If you want to maximize throughput I'd recommend checking out the ATT_MTU throughput example project here as reference at the least, as I assume you might have missed a step towards the extended data size, but I'm not able to see it right now. Are you using extended advertising for example, and what is the connection interval set to in your application?

Best regards,

Simon