How to open longrange fec function?

[Август]

Hello

    I'm testing nrf52820 longrange speed, but it's faster than my calculations. Will it automatically turn on the fec?

    This is my config below.

    m_adv_params.primary_phy   = BLE_GAP_PHY_CODED;

    m_adv_params.secondary_phy = BLE_GAP_PHY_CODED;

Below is the bag I grabbed, s=8

Test speed

This is my calculated theoretical speed(send packet 244Byte)

send packet need time

access address + ci + temr1 + pdu（header+payload）+ crc + term2 = 32bit+2bit+3bit+(244+3+2+2+2)*8*8bit+24bit*8+3bit*8 = 16445bit

speed = 16445bit/125kbit = 131.56ms

empty packet need time

access address + ci + temr1 + pdu（header）+ crc + term2  = 32bit+2bit+3bit+2*8*8bit+24bit*8+3bit*8 = 381bit

speed = 381bit/125kbit = 3.048ms

send speed 

244byte/131.56ms+3.048ms+150us*2 = 1808Byte/s

But I got 2.8kbyte/s so I think i make something wrong. Can you give me some advice?

[Susheel Nuguru]

Sorry for the delays, I could not look into this today and will come back to you mostly tomorrow. Thanks for your patience.

[Август]

Thank you It's ok.

I found another problem, when I send a packet mtu=247 will be followed by such a packet. I didn't find it in Core_v5.0.pdf

[Susheel Nuguru]

please note that every bit in the packet in in S8 Coded PHY is replicated 8 times taking the packet longer to transmit as compared to 1M PHY. Based on your connection interval, Is that what you are seeing?

[Август]

Hi 

Thank you for your response,In the packets I grabbed, I don't see the extra bytes.

When I send a packet, mtu=247 will be followed by such a packet, what is this?

[Susheel Nuguru]

That time shown below is the time from "end to start"

That means that master is not sending anything during that time. If that period is less than supeprvision timeout and the obeys slave latency, then master is allowed to send packets with that delay. You need to find out why master is delaying that packet transfer that much (assuming that nRF chip is slave here)

[Август]

Thank you I will check it.