EM7421 fails to open channel to esim

I have a small test board with an Infineon Optiga OC 1120 esim. When I try using it with the EM7421 on Windows, using MBIM, the MS_UICC_OPEN_CHANNEL fails with status 87430002 (select failed). The select is for the ISD-R as far as I understand.
Using the same board with the same esim, I get a successful result with the EM7455. I can’t upload the wireshark captures to this forum, but I can include the decoding of the MBIM traffic in txt files.
I’m also getting the same error with the EM7421 on a linux board that tries to do the same, and the problem repeats itself with a second EM7421 I have available.
Is there some configuration needed to allow the EM7421 open a channel? In both cases the terminal capabilities is sent to the modem, which should enable a connection to the ISD-R
em7455_windows_startup.txt (75.7 KB)
em7421_windows_startup.txt (78.5 KB)

I used a logic analyzer to compare how both modems interact with the eSim. I decoded the data line with Wireshark and got these results:

It seems as if both modems succeed in opening a channel and the initial SELECT ISD-R, but the EM7411 then tries to open another channel and do the same SELECT on it, which fails.
Maybe you’d have an idea what happens here @mlw @jyijyi

Hi @tomerg,

please note that status word 6999 after the SELECT ISD-R in the EM74x1 case is not a successful SELECT result, only status word 61xx from the EM7455 case is.


@rspmn I understand that. My question is why would the same eSim with the same LPA (the one from Windows) works with my EM7455, but not with the EM74x1 modems I have.

EM74x1 differ from EM7455/EM7430 in that they use a newer Qualcomm chipset and are therefore running a different firmware.

My understanding is that you are using your own custom LPA. If this is correct my suggestion would be switch to QMI-over-MBIM tunneling und the QMI UIMSAP* functionality as mentioned here EM7455 with OC1120 - AT+CSIM error or use MBIM UICC_RESET with PassThrough before the other MBIM UICC requests to avoid potential side effects.


I guess there’s a chance the new Qualcomm chipset changed something in the communication with the SIM. In the captures with the logic analyzer I was able to spot differences, but I don’t know what to look for.

We do have our own custom LPA. However, we got these results when connecting the modem to a Windows PC, which has its own LPA. We did also get it with our own LPA, but I believe it does very similar things to the Windows one, so it’s not surprising.

Can you elaborate on the UICC_RESET with PassThrough, when should it be used?

@tomerg ,
according to MB low level UICC access - Windows drivers | Microsoft Learn enabling PassThrough mode for MBIM_CID_MS_UICC_RESET before other MBIM UICC requests of your LPA should enable it to have exclusive access to the SIM while performing the LPA requests. When done disable it again for regular EM74x1 operation with your eSIM.

If there are no improvements it probably would be best to collect Qualcomm logs so that you can correlate MBIM requests from the host with internal QMI messages and SIM traffic as seen on the EM74x1.