[XTRX] How to use 1PPS input and verify it is actually taken into account?

Projects LimeSDR
1

Hello,

I am currently working with a LimeSDR XTRX (HW v2/v3, GW v3 rev7, FW v11) and trying to use an external timing setup:

External 26 MHz reference clock → working correctly
External 1PPS signal (3.3V TTL) → unclear behavior

My goal is to:

Use the 1PPS as a timing reference
Verify that the XTRX actually detects and uses the PPS

I already tried to use --syncPPS command to see the RX wait for PPS before starting but when I don’t connect a PPS, the RX starts anyway.

Regarding to this topic : Synchronise sampling start to PPS signal. · Issue #19 · myriadrf/LimeSDR_GW · GitHub
I set 0x281 = 1 (delay RX until PPS)
But same behavior on the starting PPS.

I’m quite lost on how to make this 1 PPS work. Does anyone have an idea ?

Thanks a lot !

2

Tagging @VytautasB

3

Hello Lukethomas,

Setting 0x281 to 1 and running limeTRX with --syncPPS
by default uses the internal PPS generated by the onboard GNSS chip.
on XTRX the GNSS chip generates a PPS pulse regardless of whether a GNSS fix is achieved or not.
This is the reason why the RX stream starts anyway.

To use external 1PPS signal you have to write
1 to 0xCA address.
This switches an internal mux to use the external PPS instead of the onboard GNSS PPS.

1 Like
4

Hello,

Thanks a lot !

This works perfectly !

Best