ESB lose packet, retransmit_count not work

[Lurn_Z]

Hi all:

I use SDK17.1.0, nRF52832 to develop my program.

I have two device, one is used to be PTX, another is PRX, when I send data over esb, I found a part of packet was lost, and I set retransmit_count to 1 the packet lost looks like same.

I send 90000 packet(32bytes), and received is about 89500. And retransmit_count = 0 / 1 / 3 is similar. 

1. What's wrong with it?

2. I have to send data every 2ms, What is the maximum value I can set?

Tx init code is here

uint32_t esb_tx_init(uint8_t ch, uint8_t pipe, uint8_t retrans_count)
{
    uint32_t err_code;

    nrf_esb_config_t nrf_esb_tx_config         = NRF_ESB_DEFAULT_CONFIG;
    nrf_esb_tx_config.protocol                 = NRF_ESB_PROTOCOL_ESB_DPL;
    nrf_esb_tx_config.bitrate                  = NRF_ESB_BITRATE_2MBPS;
    nrf_esb_tx_config.event_handler            = nrf_esb_event_handler;
    nrf_esb_tx_config.mode                     = NRF_ESB_MODE_PTX;
    nrf_esb_tx_config.selective_auto_ack       = false;
    nrf_esb_tx_config.retransmit_delay         = 250,
    nrf_esb_tx_config.retransmit_count         = retrans_count;
    nrf_esb_tx_config.tx_output_power          = NRF_ESB_TX_POWER_4DBM;

    tx_payload.noack = false;  //!< Flag indicating that this packet will not be acknowledgement. Flag is ignored when selective auto ack is enabled.

    err_code = nrf_esb_init(&nrf_esb_tx_config);

    VERIFY_SUCCESS(err_code);

    err_code = nrf_esb_set_base_address_0(base_addr_0);
    VERIFY_SUCCESS(err_code);

    err_code = nrf_esb_set_base_address_1(base_addr_1);
    VERIFY_SUCCESS(err_code);

    err_code = nrf_esb_set_prefixes(addr_prefix, NRF_ESB_PIPE_COUNT);
    VERIFY_SUCCESS(err_code);

    nrf_esb_set_rf_channel(ch);

    set_tx_pipe(pipe);

    return err_code;
}

By the way, what does the tx_payload.noack mean?

Best regards,

Lurn

[Kenneth]

Hi,

In a wireless system there is packet loss, and how the application handle this packet loss depend on the application. If you need to ensure that all packets are successfuly sent, then I suggest to increase the retrans_count (I think 15 is max). Even then you can experience packet loss, especially if you are at the range limit where there is very much packet loss. So if you experience max retransmit event you need to decide if you want to try again, or if you want to discard that packet and send the next instead. You write that you want to send data every 2ms, you don't however say anything about the amount of data, maybe it's better to combine the data into larger packet, so that you can send them a little less frequently, and thereby have more time to retransmit.

Kenneth

[Lurn_Z]

Hi,

Every packet is 32bytes, it will be sent every 2ms.

What's the best value about retransmit_delay for me?

And what value should I set tx_payload.noack to?

[Kenneth]

I believe the turn-around time is around 500us, so a retransmit delay of 3 should likely be a good option if you want 2ms. If you set .noack to 0, then there is no retransmit (and only 1 attempt).

Kenneth

[Lurn_Z]

OK, so your suggestions is set the retransmit_count = 3, retransmit_delay = 500, tx_payload.noack = 1.

I will try this.

Will this modification affect PRX send packet after received data?

[Kenneth]

I honestly suggest that you buy yourself an power profiler kit II (NRF-PPK2), then you will be able (by measuring the current consumption) to see exactly when it's transmitting, waiting for ack (receiving), and retransmits. You will see when changing the parameters in question how that actually affect timing on both PTX and PRX. The cost is not very high for such a precise measurement tool:
https://www.nordicsemi.com/Products/Development-hardware/Power-Profiler-Kit-2 

Video:
https://www.youtube.com/watch?v=B42lPvkUSoc 

Kenneth

[Lurn_Z]

Hi Kenneth,

Another question

if (nrf_esb_read_rx_payload(&rx_payload) == NRF_SUCCESS) 

If the above conditions do not hold, what happens next? Will it retransmit automatically, or drop the packet?

Best regards,

Lurn

[Kenneth]

Here is the description of the api: 
https://infocenter.nordicsemi.com/topic/sdk_nrf5_v17.1.0/group__nrf__esb.html#gab97b0a52736fd3acf6e377baba630d8c 

If you haven't read the documentation already, the user guide is found here:
https://infocenter.nordicsemi.com/topic/sdk_nrf5_v17.1.0/esb_users_guide.html 

Kenneth