tree 6b2713d021b869b93d22d0a0562bd2cb5fe20305
parent b7a172fa1a2adc474e1cac2ce9180260690c8d4c
author Bjarki Arge Andreasen <baa@trackunit.com> 1681142319 +0200
committer Carles Cufí <carles.cufi@nordicsemi.no> 1693396131 +0200

subsys/modem: Add modem modules

This PR adds the following modem modules to the subsys/modem
folder:

- chat: Light implementation of the Linux chat program, used to
        send and receive text based commands statically created
        scripts.

- cmux: Implementation of the CMUX protocol
- pipe: Thread-safe async data-in/data-out binding layer between
        modem  modules.

- ppp: Implementation of the PPP protocol, binding the Zephyr PPP
       L2 stack with the data-in/data-out pipe.

These modules use the abstract pipes to communicate between each
other. To bind them with the hardware, the following backends
are provided:

- TTY: modem pipe <-> POSIX TTY file
- UART: modem pipe <-> UART, async and ISR APIs supported

The backends are used to abstract away the physical layer, UART,
TTY, IPC, I2C, SPI etc, to a modem modules friendly pipe.

Signed-off-by: Bjarki Arge Andreasen <baa@trackunit.com>