Add protocol to gammu

By default gammu have support for most standard modem. I have a very particular modem with some special requirements and I would like to add a protocol to gammu. Is there a guide for this somewhere or someone who can list the basic steps for me?

EDIT: @user1664784 recommended to look att Kannel, and actually any system able to handle incoming and outgoing SMS is acceptable as long as it is stable. But I need to know how to modify the system so that I can handle a specific protocol. It is AT-based but a slight dialect. So any suggestion of a system handling SMS from a device connected over serial port is interesting. I need to find a system where someone can give me information on where in the source code I can begin adding a new AT-based protocol.

If someone have done some sample code in this area it would also be greatly appreciated.

It really depends how much different it is from standard AT commands.

• If the difference is minor (eg. needs custom initialization), it can be easily achieved by feature flags. This can be seein ATGEN_PostConnect which handles initialization for ZTE or Huawei devices.
• If the differences are big, you will probably need to write own driver, which will fall back to AT in some cases. Something similar can be seen in the AT OBEX driver which switches Bluetooth connection between OBEX and IrMC modes.

I think we used to have documentation on adding support for new devices, but I'm unable to find it right now.