nRF52840 (BMD-340-A-R) + Raspberry Pi 3B+ max MTU size does not work

RE: nRF52840 (BMD-340-A-R) + Raspberry Pi 3B+ max MTU size does not work

Duy — Wed, 13 Nov 2019 08:34:00 GMT

Thank you for your support. I think the document is enough for me. I will take time to play with the throughput and long-range demo.

Best regards,

Duy

RE: nRF52840 (BMD-340-A-R) + Raspberry Pi 3B+ max MTU size does not work

Simonr — Wed, 13 Nov 2019 08:23:12 GMT

Hi Duy

Our throughput and long-range demo (and the documentation it links to) might be able to help you understand the MTU process better. As for how to change the MTU size for the Raspberry Pi, I'm not sure how to do this, and I think that question is better suited for a Raspberry Pi forum, as we focus on Nordic products.

Best regards,

Simon

RE: nRF52840 (BMD-340-A-R) + Raspberry Pi 3B+ max MTU size does not work

Duy — Tue, 12 Nov 2019 13:57:14 GMT

Hello Simonr,

Sorry for my late reply, I don't have enough board so I had to bought one. I tested as you said and the issues lies in the Raspberry Pi. I don't know what happens inside it.

I attached log with both cases: with MTU exchange removed (work - similar to the relevant case) and without MTU exahnge removed (not work). These logs are the connection between the nRF52840 and the Raspberry Pi 3 B+.

devzone.nordicsemi.com/.../Sniffer-with-MTU-exchanged-removed.pcapng

devzone.nordicsemi.com/.../Sniffer-without-MTU-exchanged-removed.pcapng

Honestly, I don't understand well the about this MTU exchange process, do you know any helpful documents for this?

Thank you and best regards,

Duy

RE: nRF52840 (BMD-340-A-R) + Raspberry Pi 3B+ max MTU size does not work

Simonr — Wed, 23 Oct 2019 07:08:42 GMT

Have you tried connecting the Raspberry Pi to your Android phone, to confirm whether you're able to transfer more than 23 bytes between those devices? If not, I think it's safe to say that the Raspberry Pi is the common denominator in this issue.

If that's not the case, you can try sniffing the connection (between the nRF and the Raspberry Pi) using the nRF Sniffer, and upload the sniffer log here, so I can take a look at what happens between the devices when they connect and negotiate the MTU size.

Best regards,

Simon

RE: nRF52840 (BMD-340-A-R) + Raspberry Pi 3B+ max MTU size does not work

Duy — Wed, 23 Oct 2019 00:18:58 GMT

Hello Simonr,

Thank you for your answer, you understand the problem correctly.

I checks things that you told me:

[quote userid="75734" url="~/f/nordic-q-a/53446/nrf52840-bmd-340-a-r-raspberry-pi-3b-max-mtu-size-does-not-work/215904"]What are the MTU settings of the Raspberry Pi? Is that set to transfer more than 23 bytes by default? I have not looked specifically at this example, but could it be that the Raspberry Pi also uses ble_gatt.h to decide the default MTU?[/quote]

=> It is set to 247 already. There is a configuration param.

[quote userid="75734" url="~/f/nordic-q-a/53446/nrf52840-bmd-340-a-r-raspberry-pi-3b-max-mtu-size-does-not-work/215904"]Did you try the workaround from the relevant case you linked to? Please see the verified answer, and try that out.[/quote]

=> I am still working on the relevant case. Not yet work.

[quote userid="75734" url="~/f/nordic-q-a/53446/nrf52840-bmd-340-a-r-raspberry-pi-3b-max-mtu-size-does-not-work/215904"]Where in the code is the NRF_SDH_BLE_GATT_MAX_MTU_SIZE set? Are you sure that that is the MTU size that is used by the application, and not the BLE_GATT_ATT_MTU_DEFAULT?[/quote]

=> Below is the function I am using to check. I copied from an example. I also run the debug and it shows that the MTU is changed to 247 bytes.

/**@brief Function for handling events from the GATT library. */
void gatt_evt_handler(nrf_ble_gatt_t * p_gatt, nrf_ble_gatt_evt_t const * p_evt)
{
    if ((m_conn_handle == p_evt->conn_handle) && (p_evt->evt_id == NRF_BLE_GATT_EVT_ATT_MTU_UPDATED))
    {
        m_ble_nus_max_data_len = p_evt->params.att_mtu_effective - OPCODE_LENGTH - HANDLE_LENGTH;
        NRF_LOG_INFO("Data len is set to 0x%X(%d)", m_ble_nus_max_data_len, m_ble_nus_max_data_len);
    }

    m_wrench_send++;

    NRF_LOG_INFO("ATT MTU exchange completed. central 0x%x peripheral 0x%x",
                  p_gatt->att_mtu_desired_central,
                  p_gatt->att_mtu_desired_periph);
}

Best regards,

Duy

RE: nRF52840 (BMD-340-A-R) + Raspberry Pi 3B+ max MTU size does not work

Simonr — Mon, 21 Oct 2019 11:45:34 GMT

Hi Duy Tran

Let's see if I understand your problem correctly. Your nRF52840 (peripheral) is not able to receive/send more than 23 bytes when it is connected to a Raspberry Pi central, but there are no problems if the central is an Android phone for example, is that correct?

A few things you can check:

What are the MTU settings of the Raspberry Pi? Is that set to transfer more than 23 bytes by default? I have not looked specifically at this example, but could it be that the Raspberry Pi also uses ble_gatt.h to decide the default MTU?
Did you try the workaround from the relevant case you linked to? Please see the verified answer, and try that out.
Where in the code is the NRF_SDH_BLE_GATT_MAX_MTU_SIZE set? Are you sure that that is the MTU size that is used by the application, and not the BLE_GATT_ATT_MTU_DEFAULT?

Best regards,

Simon