Debugging osmo-trx constellation on XTRX SDR

Hi Thomas,

We're porting osmo-trx to our XTRX and we see some weird constellation (https://goo.gl/photos/1KycUsv26Z6T6aN97). It looks like a normal GMSK circle is there, but there is also a square like if a signal is clipped. Do you have any idea what could cause this from your previous experience?

We're running osmo-trx at 4 SPS. Then we double sample rate in software (XTRX can't handle sample rates below 2 MSPS yet) and then transmit. See first image above.

Then we tried to increase sample rate and enabled 4x interpolation in LMS7 - that led to a distorted cicrle + square constellation (https://goo.gl/photos/zMZRecxmZsqiCYMHA).