How to sync dwm1000 timer?

[Karim]

@AndyA

@Karim

6.1 External Synchronisation
This feature is used to synchronise DW1000 with external clocks or events or with other DW1000’s. For example, this would be required in a TDOA RTLS system employing wired clock synchronisation of the anchor nodes.
The DW1000 external synchronisation features allow the following functions:
a) The ability to reset the internal system counter in a deterministic way with respect to the assertion of the SYNC input pin, and an external 38.4 MHz clock supplied on the EXTCLK pin.
b) The ability to initiate the transmission of a frame in a deterministic way with respect to the assertion of the SYNC input pin, and an external 38.4 MHz clock supplied on the EXTCLK pin.
c) The ability to synchronise receive time stamping to an external counter

The SYNC input pin must be source synchronous with an external 38.4 MHz frequency reference clock supplied on the EXTCLK pin. The SYNC input pin is sampled on the rising edge of EXTCLK. Refer to the DW1000 datasheet for setup and hold times of the SYNC pin. The SYNC input provides a common reference point in time to synchronise the DW1000 with the accuracy necessary to achieve high resolution location estimation.

In paragraph “c” there is no information about the need to supply external 38.4 MHz clock on the EXTCLK.
It also says that it is synchronise receive time stamping.
I am interested in synchronizing timestamps after receiving an external SYNC. But I`m not quite understand, what is the “synchronise receive time stamping” meaning in that case? Zeroing the timestamp?
Is it possible to reset timestamp in DWM1000 using external input?

Rx timestamp is the clock value when the packet was received. “synchronise receive time stamping” means that all of your receivers set the clock to zero at the same time so that the differences in the rx timestamp accurately reflect the differences in the arrival time.

So yes it is possible to reset the timestamp using an external input.

But be very careful.

Firstly your reset will not be synchronous to the 38.4 MHz clock which gives you a 26 ns ambiguity as to when the reset actually happens, this will be different on every module.
And then after being reset the timestamp will count up based on the 38.4 MHz clock. Since each module has a different clock each one will count at a slightly different rate. Assuming the crystal trimming has been done well and each clock is +/- 0.5 ppm then 1 second after the reset your worst case timestamp difference between two modules is 1026 ns.

This is why use of the sync pin on a module isn’t encouraged. It is there and in certain special cases it may be of use. But if you want to use it to reset the timebase for a TDoA system it’s useless.

Thank you, now I see.
I just tried a rough sync via UWB and it works about 1000 times more accurately than my previous attempt. So I’ll switch my attention to wireless synchronization, and come back to the wired solution later. I have to change the PCB design.