Connect Cinterion modem with SWWAN fails with unknown error

[Sven Schwermer]

Hi all,

>> Might this imply that we're talking about the initial bearer and that
>> when MM tries to connect, because it will attempt to close any existing
>> connection, the modem is telling MM "no"?
>> 
>> We already know we need to be better about auto-detecting that the
>> initial bearer is active and should probably create a Bearer object to
>> represent it when we can figure it out. Then perhaps a connection
>> request for the same APN would just be NOP and return that already
>> created bearer? (perhaps Aleksander already implemented that, I recall
>> some discussion about it late last year)
>> 
> 
> More or less; for MBIM devices I implemented the support to show the
> initial LTE bearer information, and allow configuring it.
> But I didn't do anything yet for AT-based modems.

Is there any interaction with the modem other than the AT commands that are being logged at debug level? When I rerun all commands from the debug log with virtually identical timing, I can connect while the ModemManager fails. I ensured that the modem state is identical in both cases (+PBREADY received, PDP attached as seen by the changed APN name in the PDP list). I even verified that all replies by the modem are identical (except for the replies to AT+CCLK? Which is expected).

Since I run all AT commands just like the ModemManager and I succeed while MM doesn’t, I believe that there must be some other interaction. Perhaps via the CDC-ECM devices? I also made sure that ModemManager only talks to the first CDC-ACM which is identical to what I did in my script.

Here’s how I extracted the AT commands from the debug log (journal):
journalctl -u ModemManager -o cat | grep -E '(-->)|(<--)'

I then generated a script that replicates the AT commands via the following Python script:

import re

func = """
function cmd {
    # params: cmd, expected reply, time
    t=$(date +%s)
    echo "##################################################"
    echo "Sending command: $1"
    local reply
    reply=$(echo "$1" | /tmp/atinout - /dev/ttyACM0 -)
    if [ "$(echo "$reply" | tr -d '[:space:]')" != "$(echo "$2" | tr -d '[:space:]')" ]; then
        echo "Unexpected reply:"
        echo "$reply"
        echo "Expected:"
        echo "$2"
    fi
    sleep $(awk "BEGIN{
        delta = systime() - $t
        wait = $3 - delta
        print (wait > 0) ? wait : 0
    }")
}
"""

regex_cmd = r'\[([\d.]+)\] \(ttyACM0\): --> \'(AT.*)<CR>\''
regex_reply = r'\[([\d.]+)\] \(ttyACM0\): <-- \'(.+)\''

cmds = []
with open('/Users/sven/ModemManager/cinterion.raw.txt', 'r') as f:
    for line in f.readlines():
        match = re.match(regex_cmd, line)
        if match:
            cmds.append({
                "t": float(match[1]),
                "cmd": match[2].replace('"', '\\"'),
                "reply": ""})
        match = re.match(regex_reply, line)
        if match:
            reply = match[2].replace('<CR>', '').replace('<LF>', '\n').strip()
            reply = reply.replace('"', '\\"')
            cmds[len(cmds)-1]["reply"] += reply

print("""#!/usr/bin/env bash
set -euo pipefail
""", func)

for i, cmd in enumerate(cmds):
    t = 0
    if i < len(cmds)-1:
        t = cmds[i+1]["t"]-cmd["t"]
    print(f'cmd "{cmd["cmd"]}" "{cmd["reply"]}" "{t}”')


Any suggestions what to test next are welcome :-)

Sven