Hi all,
I'm testing Skylo NTN on nRF9151 SMA DK with the latest pre-commercial/alpha NTN modem firmware (downloaded mid-December 2025).
Registration works fine, and uplink NIDD send succeeds (#XSEND with WAITACK, #XSENDNTF confirm).
However, receiving downlink NIDD is impossible:
- #XSOCKET=1,3,0 succeeds (#XSOCKET: <id>,3,0 OK)
- #XSOCKET? confirms socket open
- #XRECV=<any timeout> (even 5s or 300s) immediately returns ERROR
I tried:
- RAI (#XSOCKETOPT=<id>,61,3) — ERROR (not supported?)
- Disabling PSM/eDRX (CPSMS=0, CEDRXS=0)
- Polling #XRECV multiple times quickly
- Events enabled (%MDMEV=2)
Is this expected behavior in the current alpha firmware?
Modem firmware version: 1.0.0-1.alpha nRF91
Using SLM Application ncs-serial-modem
Thanks for any guidance — excited for NTN but stuck on receive!
Logs:
> AT+CGMR
mfw_nrf9151-ntn_1.0.0-1.alpha
OK
> AT#XSEND=128,0,8192,"ECHO: Test msg"
#XSEND: 128,1,14
OK
%MDMEV: PRACH CE-LEVEL 0
+CSCON: 1,7,4
> AT#XRECV=5
ERROR
> AT#XRECV=5
ERROR
#XSENDNTF: 128,0,14
+CSCON: 0,7,4
> AT#XSOCKET=1,3,0
ERROR
> AT#XCLOSE=128
#XCLOSE: 128,0
OK
> AT#XSOCKET=1,3,0
#XSOCKET: 128,3,0
OK
> AT#XSEND=128,0,8192,"ECHO: Test msg"
#XSEND: 128,1,0
ERROR
> AT#XSEND=128,0,8192,"ECHO: Test msg"
#XSEND: 128,1,0
ERROR
> AT#XSEND=128,0,8192,"ECHO: Test msg"
#XSEND: 128,1,0
ERROR
> AT#XSEND=130,0,8192,"ECHO: Test msg"
#XSEND: 130,1,0
ERROR
> AT#XCLOSE=128
#XCLOSE: 128,0
OK
> AT#XSOCKET=0
ERROR
> AT#XSOCKET?
#XSOCKET: 129,3,0,3,0
#XSOCKET: 130,3,0,3,0
#XSOCKET: 131,3,0,3,0
OK
> AT#XCLOSE=129
#XCLOSE: 129,0
OK
> AT#XCLOSE=130
#XCLOSE: 130,0
OK
> AT#XCLOSE=131
#XCLOSE: 131,0
OK
> AT#XSOCKET?
OK
> AT#XSOCKET=1,3,0
#XSOCKET: 128,3,0
OK
> AT#XRECV=5
ERROR
> AT%CSCON=3
ERROR
> AT%MDMEV=2
OK
> AT#XSOCKET?
#XSOCKET: 128,3,0,3,0
OK
> AT#XSOCKETOPT=128,61,3
ERROR
> #XSOCKETOPT=128,61,3
ERROR
> AT#XSOCKET?
#XSOCKET: 128,3,0,3,0
OK
> AT#XSOCKET=1,3,0
#XSOCKET: 129,3,0
OK
> #XSOCKETOPT=129,61,3
ERROR
> AT#XRECV=120
ERROR
> AT#XSOCKET=1,3,0
#XSOCKET: 130,3,0
OK
> AT#XRECV=120
ERROR
> AT#XRECV=120
ERROR
> AT#XRECV=120
ERROR
> AT#XRECV=120
ERROR
> AT#XRECV=120
ERROR
> AT#XRECV=120
ERROR
> AT#XRECV=120
ERROR
> AT#XSOCKET=130
ERROR
> AT#XSOCKET=129
ERROR
> AT#XCLOSE=129
#XCLOSE: 129,0
OK
> AT#XCLOSE=130
#XCLOSE: 130,0
OK
> AT#XSOCKET=1,3,0
#XSOCKET: 129,3,0
OK
> AT#XRECV=300
ERROR
> AT#XRECV=800
ERROR
> AT+CPSMS=0
OK
> AT+CEDRXS=0
OK
> AT#XSOCKET=1,3,0
#XSOCKET: 130,3,0
OK
> AT#XRECV=300
ERROR
