Actual Tx duration more than estimated

Wireless Connectivity Ultra-Wideband
1

Hi,

I am using QM33120WDK1 development kit along with DW3_QM33_SDK. I am implementing a system similar to the TCFM & Listener2 application.

In the TCFM application, I have captured the timestamps at various stages. I notice that the time from when dwt_starttx(DWT_START_TX_IMMEDIATE) is called, till the point when the Tx Done Callback is received, it takes about ~316us.

As per the estimates for a frame size of 116 bytes, the total frame duration (OTA) is 232 us. Assuming an additional overheads of ~30us, the total Tx operation duration from dwt_starttx to Tx Done Callback should be ~270us.

Could anyone help to shed some insights as to what is causing the additional delay of 84us (316 - 232). The configuration I have used is as below:

static dwt_config_t config = {
9, // dwt_config_t.chan
DWT_PLEN_64, // dwt_config_t.txPreambLength
DWT_PAC8, // dwt_config.rxPAC
9, // dwt_config.txCode
9, // dwt_config.rxCode
3, // dwt_config.sfdType
DWT_BR_6M8, // dwt_config.dataRate
DWT_PHRMODE_STD, // dwt_config.phrMode
DWT_PHRRATE_STD, // dwt_config.phrRate
(64 + 1 + 8 - 8), // dwt_config.sfdTO
DWT_STS_MODE_OFF, // dwt_config.stsMode
DWT_STS_LEN_64, // dwt_config.stsLength
DWT_PDOA_M1 // dwt_config.pdoaMode
};

Thanks in advance

Markand

2

I know you have STS turned off and it may be pure coincidence but the unexplained time you are seeing is in the same region as the STS duration for the length specified.
If you change DWT_STS_LEN_64 to DWT_STS_LEN_32 do you get the callback 32 us sooner?

3

I tried changing the sts length to DWT_STS_LEN_32.

Did not notice any change in the timing. As per the DW3xxx_Driver_API_Guide_6.0.14, with the DWT_STS_MODE_OFF, the packet does not contain the STS symbols.

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4

It was a long shot but there was always the chance of an silicone bug where it waited the time anyway.

5

Hi @Markand,

If you want to know the exact duration of frame, you may need to enable PA functionality with the function below:
dwt_setlnapamode(DWT_PA_ENABLE).

And then you can capture the signal on GPIO4 (EXTTXE) using SALEAE for example.

Hope it helps,
Wassim