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Thread: nRF24L01+ OTA Timing Measurements

  1. #1
    Old Man Winter member sporadic's Avatar
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    nRF24L01+ OTA Timing Measurements

    I had posted some of this on the other site last year, but it was buried in a thread on latency. With the recent talks of nRF24L01+ performance, this may help some people figure out rough timing information.

    According to the datasheet, the "Time On Air" is (8(1+addr_len+payload_len+crc_len)+9)/datarate. Using a 5 byte address, 32 byte payload, and 2 byte CRC, (RFShowControl packet configuration), I did some tests at the available datarates. Using the nRF24L01+ interrupts, below is what I came up with. For the CE signals, measurements started 15us into the CE pulse (radio requires 10us per datasheet).

    Measurements were done on a scope (Rigol DS1052E), using the built-in measuring functions. Trigger was the CE rising edge of the transmitter. Times are the delay between the CE falling edge and interrupt falling edge (active low). CE was being pulsed high for 15us, so theoretically you could shave 5us off all the observed times. The times tended to jump 4us up and down so what I noted was the perceived average. Hardware used were two of my nRFbridge transceivers with nRF24L01+ "ZigZag" modules.

    250kbps data rate
    ToA from datasheet calculation: 1316us
    Time between CE (TX powerup) and TX_DS interrupt (on transmitter): 1408us
    Time between CE (TX powerup) and RX_DR interrupt (on receiver): 1432us

    1Mbps
    ToA from datasheet calculation: 329us
    Time between CE (TX powerup) and TX_DS interrupt (on transmitter): 440us
    Time between CE (TX powerup) and RX_DR interrupt (on receiver): 444us

    2Mbps
    ToA from datasheet calculation: 164.5us
    Time between CE (TX powerup) and TX_DS interrupt (on transmitter): 277us
    Time between CE (TX powerup) and RX_DR interrupt (on receiver): 283us

  2. #2
    Rudolph member Ellis's Avatar
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    I love numbers. I don't have a scope at home, so thank you for providing these.
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  3. #3
    Frosty member
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    This would pretty much confirm my thoughts that the Arduino was the time lag in my Komby system for my LED jacket.

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