[Mesh] Decreasing the data rate causes an assert.

Question

Hi team,

I'm using Mesh in my project.
Using this thread as a reference, I tried to decrease the data throughput and experiment to see if devices could communicate with each other even further away.
< https://devzone.nordicsemi.com/f/nordic-q-a/29813/change-phy-in-mesh >

In the default state (1M) before the change, the device worked fine.
However, when I flush the device with the changes shown in the thread and make it work with "RADIO_MODE_NRF_62K5BIT", I get a log of assertion.

When I checked the asserted part with addr2line, I saw the line "NRF_MESH_ASSERT (TIMER_OLDER_THAN (time_now, m_end_time));" in "end_handle ()" of "bearer_handler.c".

[Development environment]
・nrf5_SDK_for_Mesh_v4.0.0_src
・nRF5_SDK_16.0.0_98a08e2
・nrf52840 Soc
[Test with]
・nrf5_SDK_for_Mesh_v4.0.0_src\examples\light_switch\server
・nrf5_SDK_for_Mesh_v4.0.0_src\examples\serial

For the sake of review, I'll describe the changes I made by referencing the thread.

1. Changed p_broadcast-> params.radio_config.radio_mode written in set_default_broadcast_configuration () of advertiser.c from "RADIO_MODE_BLE_1MBIT" to "RADIO_MODE_NRF_62K5BIT"
2. Changed the argument of scanner_config_radio_mode_set () written in scanner_config_reset () of scanner.c from "RADIO_MODE_BLE_1MBIT" to "RADIO_MODE_NRF_62K5BIT"
3. Add the following code to the end of radio_config_config () in radio_config.c

    if (p_config->radio_mode == RADIO_MODE_NRF_62K5BIT)
    {
        NRF_RADIO->PCNF0 |= (
            ((RADIO_PCNF0_PLEN_LongRange << RADIO_PCNF0_PLEN_Pos) & RADIO_PCNF0_PLEN_Msk) |
            ((2 << RADIO_PCNF0_CILEN_Pos) & RADIO_PCNF0_CILEN_Msk) |
            ((3 << RADIO_PCNF0_TERMLEN_Pos) & RADIO_PCNF0_TERMLEN_Msk) );
    }

4. Add the following code to time_required_to_send_us () in broadcast.c

    if (radio_mode == RADIO_MODE_NRF_62K5BIT)
    {
        packet_length_in_bytes += RADIO_PREAMBLE_LENGTH_LR_EXTRA_BYTES;
    }

5. Changed the 5th initializer of the radio_mode_to_us_per_byte array declared in time_required_to_send_us () in broadcast.c from "128" to "64"
6. Added the following define to broadcast.c

#define RADIO_PREAMBLE_LENGTH_LR_EXTRA_BYTES 9

Please let me know if there are any other areas that need to be modified to avoid assertion.
Also, if there are any things that I should be concerned about when decreasing the data throughput, (degree of influence on other processing), please let me know as well.

Best regards,
Wataru

Mttrinh · Accepted Answer

Hi, 
 I'm not sure why you are getting the assertion. Have you made any other modifications other than the ones you metioned above? 
 Note that the Bluetooth Mesh Profile Specification is based on Bluetooth v4.0, with the intention of allowing BLE devices already in the market to interact with Bluetooth Mesh networks. Hence, Bluetooth 5 features such as long range isn't supported. Which means your end product, if using any Bluetooth 5 features, won't be certified as it doesn't comply with the specification.

[Mesh] Decreasing the data rate causes an assert.

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