Increase max packets

[Alaa]

Hi,

I'm using BLE on nrf52832 and softdevice s132. It seems that when I send too many packets (around 45), the ble crashes. Is there a way to increase that number or at least make it not crash?

Thanks

[awneil]

What BLE profile are you using - eg, NUS?

You should get an error status telling you when the SD can't accept more packets - are you paying attention to that?

[Alaa]

NUS profile (uart).

To clarify, the crash happens when I send data from microcontroller STM32 to the nordic nrf52 that's connected to it via uart, and then send the data to a smartphone by BLE.

What error should I get? I looked through the error codes (0 to 19) and I can't find anything related to accepting packets.

Also, if I get this error, what can I do?

Here's some of the code inside uart_event_handle() under the case APP_UART_DATA_READY:

do
{
    uint16_t length = (uint16_t)index;
    err_code = ble_nus_string_send(&m_nus, data_array, &length);
    if ( (err_code != NRF_ERROR_INVALID_STATE) && (err_code != NRF_ERROR_RESOURCES) )
    {
        APP_ERROR_CHECK(err_code);
    }
} while (err_code == NRF_ERROR_RESOURCES);

Or should I be looking somewhere else?

Thanks

[awneil]

You need to investigate to see what happens immediately before the crash.

Maybe you're getting NRF_ERROR_RESOURCES - that sounds a likely candidate, doesn't it?

Instrument your code to see what's happening.

Alaa said:

if I get this error, what can I do?

The link has a finite capacity - you can't just keep chucking data at it over that capacity.

Only you can decide what's appropriate for your application in this situation

• just discard excess data?
• if the data is "bursty", buffer it somewhere?
• tell the STM32 to stop sending data?
• compress the data?
• decimate the data?
• adjust the link parameters to increase throughput?
• etc, etc, ...

[Alaa]

Thanks for the response,

I verified that the error that I'm getting is NRF_ERROR_RESOURCES.

Regarding the capacity, let's say maximum packets is 40 of size 20. Does that mean that if I send, say 40 packets of size 20, then wait some time, and then continue sending, it will work successfully? How much should the waiting time be?

Thank you

[awneil]

Arbitrary delays are never a good idea.

Better to look for a specific indication that the link again has capacity.

If you are constantly hitting this, it indicates that you need to re-evaluate something - either send less data, or adjust the link parameters to increase throughput

[Alaa]

Can you tell me what parameters to adjust?

I just tried adding a 500 ms delay after roughly 40 packets, and I'm not getting the error anymore.

[awneil]

Connection interval

MTU size

Use the 2Mbps PHY (BLE 5 High troughput mode)


https://www.nordicsemi.com/Products/Low-power-short-range-wireless/Bluetooth-5

But remember that your Central (especially if it's a phone or tablet) may impose limits ...