Max packet number per CI for nRF5340

[PengLiu]

Hi, Experts,

We are evaluating BLE throughput (sdk-nrf-2.7.0 throughput sample) using nRF5340DKs. The CI is set to 6 i.e. 7.5ms. The PDU size is set to 251, PHY is 2Mbps.

The measured throughput is around 1040kbps, far less than the theoretical value 1300kbps.

The times include transmitting + IFS + receiving + IFS is 1400us, so the theoretical packet number within 7.5ms is calculated as 7500/1400=5. We suspects packet number of 4 is used instead of 5, thus the actual rate is 80% of theoretical value. Can anyone help confirm whether packet number of 4 is used for this case and for what reason the number is reduced by 1.

Thanks,

Peng,

[PengLiu]

Hi, Hung,

Can you elaborate a little about "the scheduler need to be able to fit the maximum payload possible of a pair of TX&RX in to the slot (worst case scenario). "

Does this mean in the standby period of one CI, the scheduler fills in the data package in TX FIFO for the first transmission in next CI? if this is not done, in the beginning of next CI, TX FIFO has to be filled first for the first package data, thus adding waiting time(standby time)?

Thanks,

Peng,

[Hung Bui]

Hi Peng, 

No what I mean is that to be able to fit 5 packets in stead of 4 the scheduler need to be sure the 5th slot has to be big enough to receive max size RX packet. Usually it's an empty packet (the RX) but it can't be guarantee that it's always an empty packet, the peripheral can send a packet with max size. So that's why it can only fit 4 packets. The solution is to increase the CI so that the 5th packet can fit.