Accurate timestamps from nRF boards?

[Elm]

Hi,

I would like to have accurate (1-5ms), synchronized timestamps for logging events from a set of nRF5x boards, spaced tens of meters apart. Each nRF5x board is connected to a Rapberry Pi, and each RPi forwards RTT logging messages using the JLink.exe program over its Ethernet port to a central location.

The purpose would be to correlate events in all nRF5x bards.

As the JLink.exe program just relays RTT traffic from the boards using TCP ("Telnet") to a central location, it is not easy to insert traffic into the RTT stream.

One possibility that I consider is to synchronize the RPis using ntpd(8), and somehow generate pulses from ntpd on a RPi GPIO pins, and to connect that pin to a nRF5x GPIO pin. The nRF5x GPIO pin would then generate an interrupt that sets the clock to a certain time. However, I have not seen any means of exporting e.g. PPS pulses from ntpd, only to import pulses. This idea requires a fair amount of work.

Do you have any other idea on how to synchronize logs with this accuracy?

regards Elm

[Matt]

A (cheaper) alternative is to connect the nRF5x chip/module (not DK, hence no JLink OB) to RasPi through the uart (assuming the nRF5x uart is available!). Then run a rtc with 1ms accuracy in the nRF5x and imbed that local timestamp into the log, and forward the log to RasPi through uart, and have a daemon maintains the GMT and thus convert the local timestamp to a global one. The RasPi needs to get the GMT from somewhere, be it from the gmt website or from another GSM module (eg. a Telit GE866) connected to it.