Dear All,
   I made a new project with the Simcom SIM800C GPRS chip.

The module has two serial port that are connected to a CP2016 
USB-to-UART chip. After some work i get the module working with the 
sim900 driver that supports also the SIM800.
I can dial numbers read and sen SMS messages, etc, etc. I works fine.

Now, I have problem with the gprs connection.
I cannot use the official testing programs because they require python 
that is not available in my poor buildroot rootfs, but I have the 
dbus-send utility.

Here is the situation.

The modem is up and ruinning:

# dbus-send --system --print-reply --dest=org.ofono / 
org.ofono.Manager.GetModems
method return time=1557938457.226027 sender=:1.3 -> destination=:1.22 
serial=79 reply_serial=2
    array [
       struct {
          object path "/sim900_0"
          array [
             dict entry(
                string "Online"
                variant                   boolean true
             )
             dict entry(
                string "Powered"
                variant                   boolean true
             )
             dict entry(
                string "Lockdown"
                variant                   boolean false
             )
             dict entry(
                string "Emergency"
                variant                   boolean false
             )
             dict entry(
                string "Manufacturer"
                variant                   string "SIMCOM_Ltd"
             )
             dict entry(
                string "Model"
                variant                   string "SIMCOM_SIM800C"
             )
             dict entry(
                string "Revision"
                variant                   string "Revision:1418B06SIM800C24"
             )
             dict entry(
                string "Serial"
                variant                   string "869270046863956"
             )
             dict entry(
                string "SystemPath"
                variant                   string 
"/sys/devices/soc0/soc/2100000.aips-bus/2184200.usb/ci_hdrc.1/usb1/1-1/1-1.1/1-1.1:1.1/ttyUSB1"
             )
             dict entry(
                string "Interfaces"
                variant                   array [
                      string "org.ofono.Phonebook"
                      string "org.ofono.SmartMessaging"
                      string "org.ofono.PushNotification"
                      string "org.ofono.MessageManager"
                      string "org.ofono.CallVolume"
                      string "org.ofono.VoiceCallManager"
                      string "org.ofono.ConnectionManager"
                      string "org.ofono.SupplementaryServices"
                      string "org.ofono.NetworkRegistration"
                      string "org.ofono.AllowedAccessPoints"
                      string "org.ofono.SimManager"
                   ]
             )
             dict entry(
                string "Features"
                variant                   array [
                      string "sms"
                      string "gprs"
                      string "ussd"
                      string "net"
                      string "sim"
                   ]
             )
             dict entry(
                string "Type"
                variant                   string "hardware"
             )
          ]
       }
    ]


I created a new internet context with a working configuration (tested in 
another platform):


# dbus-send --system --print-reply --dest=org.ofono /sim900_0/context1 
org.ofono.ConnectionContext.GetProperties
method return time=1557937482.290288 sender=:1.3 -> destination=:1.17 
serial=71 reply_serial=2
    array [
       dict entry(
          string "Name"
          variant             string "Internet"
       )
       dict entry(
          string "Active"
          variant             boolean false
       )
       dict entry(
          string "Type"
          variant             string "internet"
       )
       dict entry(
          string "Protocol"
          variant             string "ip"
       )
       dict entry(
          string "AccessPointName"
          variant             string "tre.it"
       )
       dict entry(
          string "Username"
          variant             string "user"
       )
       dict entry(
          string "Password"
          variant             string "password"
       )
       dict entry(
          string "AuthenticationMethod"
          variant             string "pap"
       )
       dict entry(
          string "Settings"
          variant             array [
             ]
       )
       dict entry(
          string "IPv6.Settings"
          variant             array [
             ]
       )
    ]

but when I try to Activate the context it gives me this error:

# dbus-send --system --print-reply --dest=org.ofono /sim900_0/context1 
org.ofono.ConnectionContext.SetProperty string:"Active" variant:boolean:true
Error org.ofono.Error.NotImplemented: Implementation not provided

and the "Active" property stay false.

What's wrong?

Any suggestion is very appreciated.