======Issues with glinet modem compatibility======

=====A list of useful info=====

  /usr/bin/gl_modem                ## The gl_modem binary
  /lib/netifd/proto/ncm.sh         ## Part of netifd
  /lib/netifd/netifd-proto.sh      ## More netifd
  /usr/bin/modem_network_recover_detection.sh  ## part of glinet kmwan for fixing broken connections.
  ls -l  /usr/bin/modem*
  
Modem details:
  # This is for a Huawei E3372-320h
  Vendor=12d1 ProdID=155e Rev= 1.02
  
AT Commands:
  ATI
  AT+CPIN?
  AT^ICCID?
    ^ICCID: 8912345678987654321  # Not the real iccid!
    OK
  AT^NDISDUP=1,1,"giffgaff.com"

drop pdp for testing
  gl_modem -B 1-1 AT 'AT+CGACT=0,1'

bring pdp up:
  gl_modem -B 1-1 AT 'AT+CGACT=1,1'
 

OS and uci peek and poke:
  ls -l /var/usbnode/1-1/modem/
  cat /var/state/network
  uci -P /var/state show network.wwan.ifname
    network.wwan.ifname='wwan0'
  uci -P /var/state show network.modem_1_1.ifname
    network.modem_1_1.ifname='wwan0'
  uci -P /var/state show
  uci -q get glmodem.global.log_level

Databases:
  /www/js/apns-full-conf.json.gz      ## An isp apn list in the firmware that gets unzipped to...
  /var/run/modem/apns-full-conf.json  ## ...here. If it exists already it doesn't get re-unzipped.
  
I added giffgaff entry to the apns-full-conf.json files above:
<code>
   {
      "-carrier": "giffgaff",
      "-carrier_id": "2118",
      "-mcc": "234",
      "-mnc": "10",
      "-apn": "giffgaff.com",
      "-type": "default,ia,supl,mms,xcap"
    },
    {
      "-carrier": "giffgaff",
      "-carrier_id": "2118",
      "-mcc": "234",
      "-mnc": "105",
      "-apn": "giffgaff.com",
      "-type": "default,ia,supl,mms,xcap"
    },
</code>

Sniffing the calls made to gl_modem:
<code>
# A shim to wrap around gl_modem to sniff calling info and processes.
nano /usr/bin/gl_modem

#!/bin/sh
# Stub wrapper for gl_modem to log calls and forward to the real binary
logger -p notice -t gl_modem_AndyFix "gl_modem called args: $*"

# Run the real binary with all arguments, capture its exit code
/usr/bin/gl_modem.patched4 "$@"
ret=$?

# Log the exit code
logger -p notice -t gl_modem_AndyFix "gl_modem exit code: $ret"

# Propagate the exit code back to the caller
exit $ret
</code>




=====Errors in the logs and what they probably mean=====
====Failed to get iccid====
===The Problem===
If you see this in the logs:
  Wed Dec 17 07:15:17 2025 daemon.info gl_modem: (modem_cm.c:1324) Enter the dialing process
  Wed Dec 17 07:15:17 2025 daemon.err gl_modem: (modem_cm.c:1343) Failed to get iccid, maybe PIN code is locked,please check!
  
It probably means the sim is returning a 19 digit iccid. gl_modem is hardcoded to look for 20 digits.\\
===The fix: Patch /usr/bin/gl_modem:===
At file address 019990 change:
  BF 52 00 71     cmp        w21,#0x14      // 20 digit check
to
  BF 4E 00 71     cmp        w21,#0x13      // 19 digit check
  

=====glinet gl_modem hacking=====
====Why and what did we achieve====
gl_modem has a lookup table for each modem it recognises and a list of functions it can call to do various things.\\
\\
The idea (i think) is that the command gl_m#odem -B 1-1 connect-auto uses this table and the info in the apn database to setup the modem and populate a config interface xxxx in /etc/config/network as if by magic.

====Useful binary info====
modem_head is the start of the table at 029000 in the file, 439000 in the ghidra project.\\

Modem Struct E3372 Model ID:
  (029DE0) 00439de0 5E 15 00 00     int32_t         155Eh                modem_productid
  (-29e88) 00000000 Remove modem_get_sim_mcc_mnc call, not supported.