It may make sense if the purpose is transfer of time from node to node for the purposes other than location. For example, using an UWB signal to precisely synchronize wireless nodes to transmit at exact the right times. Perhaps that synchronization is adequate if it is within a few 10s of nanoseconds, and some MCUs can run timers that can capture fast.
In our experience, the IRQ interrupt from the DW1000 on packet SFD is quite precisely aligned with the packet reception. It has about a +/- 4 ns jitter, which comes from the alignment of the internal 124.8 MHz clock of the subsystem inside the DW1000. We use this time mark for precisely aligning the DW1000 time to the processor time using a timer capture input, and then we use that for network slot timing. You can’t use an interrupt routine to do this due to interrupt latency, you must capture the edge in hardware. This is one reason we can do thousands of locates per second in our system.
I don’t know if the SFDLED output is as accurate as the IRQ output. That is something you would have to test. I give it a fair chance it is as accurate, but that’s just using my intuition as to how it would be implemented internally to the DW1000.
Once you have the timer capture on IRQ, you can then read the packet RX_TIME and now you have a precise relationship between the packet arrival time the DW1000 recorded and the processor timer.
If your hardware allows (most don’t), you could run the timer on the same 38.4 MHz clock that runs the DW1000. If you do that, then you only need to learn the offset between them one time and you don’t have to worry about frequency drift.
If you want accurate correlation between DW1000 time and a processor counter, using a timer capture on the IRQ (or maybe the SFDLED) will perform much better than using SPI to read SYS_TIME. The uncertainties with the timer capture are very small, +/- 4 ns due to DW1000 jitter, and then whatever your timer clock period is (20 ns for a 50 MHz clock, say). If your MCU timer is limited in speed, that will hurt precision, of course. It is useful to have a 32 bit counter for this work since it runs at high speed.
Mike Ciholas, President, Ciholas, Inc
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