Can´t Receive or make calls on LTE (Modem not falling back to 2G when a call is received)

[Sig2018]

I own a A7670SA working fine with MQTT connection. I'm also able to receive and send SMS. But voice call doesn't work on LTE(4G). The only way to make it work is to force module to GSM(2G). I guess there is some problem with network handshake when it request the CSFB (Circuit Switch Fallback) since VoLTE is not supported. Can anyone help with any way to debug? I've tried with different SIMs from different carriers, TinyGSM and AT commands with same result: NO call when in LTE Tank you in advance for any help.

[lewisxhe]

First confirm whether the sim card supports volte, put the volte-supported card into the phone and try to see if it can browse the web when making calls. After confirming that it is OK in the phone, put it into the board for testing. VOLTE does not require special settings, as long as the card supports volte, it will automatically select

[Sig2018]

Thank you. No, Sim doesn't support VoLTE. As I said I'm looking for the modem to fall back to 2G. Is that possible?

[lewisxhe]

SIMCom technicians told me that all A7670 series support VOLTE and no additional settings are required.

[Sig2018]

But I-m not asking about VoLTE. I-m asking about fallback to 2G when an incoming call is received.

[lewisxhe]

AT+CNMP=13 Only 2G connections are allowed

[Sig2018]

I had selected 2 (automatic). In other modems and phones if VoLTE is not available it will switch to 2G when an incoming call is received. But Usually it will connect to LTE for data. I need to use the board normally in LTE but be able to switch to 2G automatically when a call is receive. I just chaged Issue subject to make it more clear. Is it possible?

[lewisxhe]

As far as I know if Volte is not available then the demodulator will automatically switch modes

[Sig2018]

Is not working. If module is in LTE there is not fall back to to 2g. SMS are received on LTE but call cannot be delivered. The caller receive a message the custom is not available but in fact it is because right after caller hang up an SMS arrives saying: a caller wit number (caller number) just call you. Can you talk to Simcom engineers to see if there is any way to fix it?

[lewisxhe]

Do you mean that if the current module is in the LTE network, if a call comes in, the modem will not be able to receive the call notification? Cannot answer the call?

[Sig2018]

If an LTE SIM with Not VoLTE service is plugged on a modem from any other brand or a phone the network instruct the modem to switch to 3G or 2G and then call is received. In your board apparently there is some missing setting because when modem is on LTE nothing happen when call is on connection state and caller receive a message saying customer (lilygo A7670) is not available. However customer is available and connected to LTE data and able to receive SMS too. The problem is Fallback to 2G is not happening: Can you ask SIMCOM about this issue??

[lewisxhe]

So if it is in the GSM network, I can answer and make calls, right?

[lewisxhe]

SIMCOM's reply to me: The operator notifies the module to switch 2G/LTE, and the user does not need to intervene If the SIM card used does not support 2G voice calls, then 2G cannot be called in the case of LTE

[Sig2018]

Well is not working as SIMCOM say. The SIM do support 2G calls, when I force the modem to 2G permanent the calls are received. But en Auto mode if Modem is on LTE call does not work. I've tried with 3 SIMs from different operator so it is not a network or service problem but a Modem Problem. Maybe you can share with me the SIMCOM contact and I can do some test with their guidance. Or you can told them and transfer what they say to me.

[lewisxhe]

SIMCOM needs your device's running log to further analyze the problem.

1. Please download the tools needed to run the capture log here
2. Please write ATDebug to the board, just turn on the modem
3. Prepare the preliminary work of capturing the log according to the steps in the document
4. When ready to capture
   • Manually send AT+CFUN=0, then wait for a few seconds
   • Send AT+CFUN=1 to exit the flight mode
   • Wait for network registration, send AT+CPSI? Check whether the current network enters LTE
   • Send ATD123456; Dial the phone, replace 123456 with the mobile phone number, wait for ten seconds and hang up
   • Then use another mobile phone to call the SIM card of the modem After waiting for thirty seconds, use the provided tool to export the log file, and then send it to me, I will forward it to SIMCOM for analysis

Tips, when capturing logs, the USB-C of the board is powered MicroUSB is the capture port of the modem, if there is no driver, you can find it here

[Sig2018]

Hi @lewisxhe I think I have the requested log(There are a couple of options on tool and the instructions were not really detailed)

However there is an error when I try to place call(please see below) so not sure if we will get something. Where should I upload the log? I wouldn't like to upload here since I think there si some sensible UE and SIM information on log.

15:07:55.795 -> 15:07:55.795 -> +CGEV: NW PDN DEACT 1 15:07:56.238 -> 15:07:56.280 -> OK 15:08:03.715 -> AT+CFUN=1

15:08:06.370 -> OK 15:08:06.719 -> 15:08:06.719 -> +CPIN: READY 15:08:07.672 -> 15:08:07.672 -> SMS DONE 15:08:15.251 -> 15:08:15.251 -> +CGEV: EPS PDN ACT 1 15:08:16.268 -> 15:08:16.268 -> +CGEV: ME PDN DEACT 8 15:08:17.187 -> 15:08:17.224 -> PB DONE 15:08:24.699 -> AT+CPSI?

15:08:24.731 -> +CPSI: LTE,Online,730-01,0x333B,3092229,271,EUTRAN-BAND28,9485,4,0,7,53,58,-3 15:08:24.804 -> 15:08:24.804 -> OK 15:08:33.826 -> ATD99XXXXXXX

15:08:33.867 -> ERROR

[lewisxhe]

ATD + mobile phone number + ; end character

[Sig2018]

OK, so it is not working but command is accepted now. Where should I upload the log file?

21:33:50.275 -> atd97xxxxxxxx; 21:33:50.485 -> +CLCC: 1,0,2,0,0,"97xxxxxxxx",129,"",,0 21:33:50.531 -> 21:33:50.577 -> OK 21:34:26.917 -> 21:34:26.917 -> +CLCC: 1,0,6,0,0,"97xxxxxxx",129,"",,0 21:34:26.949 -> 21:34:26.981 -> NO CARRIER

[lewisxhe]

Have you connected the microphone and lama? If not, you cannot make calls.

[Sig2018]

I didn't yet but anyway I will need to receive calls and it is not working. It is a modem problem because on 2G calls are received, didn't try sound but I can get ring message and also caller ID. Does Not happen on LTE. Where should I upload the log file?

[lewisxhe]

According to the method mentioned above, after recording the log, paste the exported compressed package on gaithub.

[Sig2018]

OK here you have the log: https://github.com/Sig2018/SIM7670SA Please confirm you are able to download.

[lewisxhe]

OK, I will send it to SIMCOM for them to check. I will reply here if there is any news.

[lewisxhe]

You need to provide me with the version information of the modem you are using and send me the QR code on the label of the camera module.

[Sig2018]

AT+CGMM A7670SA-LASE AT+CGMR +CGMR: A011B19A7670M7

What do you mean by camera module?

[lewisxhe]

Use at+simcomati to query the results

[Sig2018]

at+simcomati

Manufacturer: INCORPORATED Model: A7670SA-LASE Revision: A011B19A7670M7 A7670M7_B19V01_240126 QCN: IMEI: 863829074xxxxxx MEID: +GCAP: +CGSM,+FCLASS,+DS DeviceInfo:

[lewisxhe]

OK

[lewisxhe]

SIMCOM cannot extract the log you sent. Please upgrade the latest firmware and test again. If it still doesn't work, please send AT+MEDCR=0,161,16, then send AT+CFUN=0, wait a few seconds and then send AT+CFUN=1, and try again. If it still doesn't work, please use this firmware to capture the log. Please refer to the upgrade document and video here https://github.com/Xinyuan-LilyGO/LilyGO-T-A76XX/blob/main/docs/update_fw.md

[Sig2018]

Could you explain how to check the version of firmware I have and the latest one, changes, etc? On the page you pointed there is not a clear reference of firmware version just a link to download. I won't just download a file and make an upgrade not knowing what it is on it, with a high risk to brick the device. The documentation is poor and needs to be improved. IN the other hand the logs I sent are readable. I can upload files not compressed if you want or if Simcom can tell me what particular file they are looking for I could check it.

[Sig2018]

As you can see log is being captured. There are a lot of red lines related with some come COM warning, maybe that is causing troubles to SIMCOM.

[Sig2018]

Just Uploaded a new log. https://github.com/Sig2018/SIM7670SA To check if they can see now.

[lewisxhe]

Here is the upgrade video, have you watched it? Send AT+SIMCOMATI to check the current version https://github.com/Xinyuan-LilyGO/LilyGO-T-A76XX/blob/main/docs/update_fw.md#record-video

[lewisxhe]

SIMCOM responded:

Please send

1. AT+MEDCR=0,161,16
2. AT+CFUN=0, wait a few seconds
3. AT+CFUN=1
4. Wait for network registration to complete
5. After connecting to the LTE network, make a phone call
6. Then call A7670 from other mobile phones
7. Wait 30 seconds to export the log file and send it to me again

[Sig2018]

Hi @lewisxhe Did you check the second version of the log I've uploaded?

[lewisxhe]

I sent Log 2024-08-22 12;58;37.168.zip to SIMCOM and got the following reply:

[Sig2018]

I think you forgot to copy the reply

[lewisxhe]

SIMCOM responded:

Please send

1. AT+MEDCR=0,161,16
2. AT+CFUN=0, wait a few seconds
3. AT+CFUN=1
4. Wait for network registration to complete
5. After connecting to the LTE network, make a phone call
6. Then call A7670 from other mobile phones
7. Wait 30 seconds to export the log file and send it to me again

This is the reply

[Sig2018]

Log Upladed https://github.com/Sig2018/SIM7670SA/blob/main/Log%202024-08-30%2013%3B41%3B53.392.zip

[Sig2018]

@lewisxhe Any answer with log?

[lewisxhe]

@Sig2018 SIMCom reports that you need to upgrade to the latest firmware before capturing logs. Maybe the new firmware has fixed something.

To prevent misunderstanding, I will reorganize Simcom's requirements

1. Upgrade to the latest firmware. Please see here for how to upgrade. Find the corresponding firmware here for upgrade. https://github.com/Xinyuan-LilyGO/LilyGO-T-A76XX/blob/main/docs/update_fw.md#record-video
2. After the upgrade is complete, send AT+SIMCOMATI to check whether the upgrade is successful.
3. Then open the log capture tool. Here is a video of capturing logs. https://www.youtube.com/watch?v=31MUyhX5UHs
4. Then use the serial tool to send AT commands interactively
5. AT+MEDCR=0,161,16
6. AT+CFUN=0, wait a few seconds
7. AT+CFUN=1
8. Wait for network registration to complete
9. After connecting to the LTE network, make a phone call
10. Then call A7670 from other mobile phones
11. Wait 30 seconds to export the log file and send it to me again

[Sig2018]

After having some time to update the firmware the one I've downloaded is exactly the Same the modem already had. All the update process run well and said the upgrade was successful as you show on video. But now it can't register on network. So I not only have one problem but 2. Can you help?

UPDATE: After playing with AT commands and set the APN,it is now working.

But I still have same problem with Calls not falling back to 2G and if I capture the log SIMCOM will say again to upgrade firmware ( which I did) and it is the last one available that is already installed.

[Sig2018]

[lewisxhe]

Do you mean after upgrading the firmware, the problem still exists, but log capture is not available?

[Sig2018]

No i mean: I already sent two logs following the procedure. SIMCOM requested to send it again after upgrading firmware but firmware was already the latest available so : Why SIMCOM cannot tell me what the problem is with the logs I already sent if the firmware is already the last one? It looks there some disconnection between what they ask and what I sent. Are they really looking at my logs?

[lewisxhe]

Sorry, it was SIMCOM that made a mistake. You need to update to the correct version A011B21V01A7670M7 and then provide the log again according to the above method.

[github-actions[bot]]

This issue is stale because it has been open for 30 days with no activity.