espressif/eppp_link

readme

# ESP PPP Link component (eppp_link)

The component provides a general purpose connectivity engine between two microcontrollers, one acting as PPP server, the other one as PPP client.
This component could be used for extending network using physical serial connection. Applications could vary from providing PRC engine for multiprocessor solutions to serial connection to POSIX machine. This uses a standard PPP protocol (if enabled) to negotiate IP addresses and networking, so standard PPP toolset could be used, e.g. a `pppd` service on linux. Typical application is a WiFi connectivity provider for chips that do not have WiFi.
Uses simplified TUN network interface by default to enable faster data transfer on non-UART transports.

## Typical application

Using this component we can construct a WiFi connectivity gateway on PPP channel. The below diagram depicts an application where
PPP server is running on a WiFi capable chip with NAPT module translating packets between WiFi and PPPoS interface.
We usually call this node a communication coprocessor, or a "SLAVE" microcontroller.
The main microcontroller (sometimes also called the "HOST") runs PPP client and connects only to the serial line,
brings in the WiFi connectivity from the communication coprocessor.

```
        Communication coprocessor                        Main microcontroller
    \|/  +----------------+                               +----------------+
     |   |                |       (serial) line           |                |
     +---+ WiFi NAT PPPoS |=== UART / SPI / SDIO / ETH ===| PPPoS client   |
         |        (server)|                               |                |
         +----------------+                               +----------------+
```

## Configuration

### Choose the transport layer

Use `idf.py menuconfig` to select the transport layer:

* `CONFIG_EPPP_LINK_UART` -- Use UART transport layer
* `CONFIG_EPPP_LINK_SPI` -- Use SPI transport layer
* `CONFIG_EPPP_LINK_SDIO` -- Use SDIO transport layer
* `CONFIG_EPPP_LINK_ETHERNET` -- Use Ethernet transport
  - Note: Ethernet creates it's own task, so calling `eppp_perform()` would not work
  - Note: Add dependency to ethernet_init component to use other Ethernet drivers
  - Note: You can override functions `eppp_transport_ethernet_deinit()` and `eppp_transport_ethernet_init()` to use your own Ethernet driver

### Choose the network interface

Use PPP netif for UART; Keep the default (TUN) for others


## API

### Client

* `eppp_connect()` -- Simplified API. Provides the initialization, starts the task and blocks until we're connected

### Server

* `eppp_listen()` -- Simplified API. Provides the initialization, starts the task and blocks until the client connects

### Manual actions

* `eppp_init()` -- Initializes one endpoint (client/server).
* `eppp_deinit()` -- Destroys the endpoint
* `eppp_netif_start()` -- Starts the network, could be called after startup or whenever a connection is lost
* `eppp_netif_stop()` --  Stops the network
* `eppp_perform()` -- Perform one iteration of the PPP task (need to be called regularly in task-less configuration)

## Throughput

Tested with WiFi-NAPT example

### UART @ 3Mbauds

* TCP - 2Mbits/s
* UDP - 2Mbits/s

### SPI @ 16MHz

* TCP - 5Mbits/s
* UDP - 8Mbits/s

### SDIO

* TCP - 9Mbits/s
* UDP - 11Mbits/s

### Ethernet

- Internal EMAC with real PHY chip
    * TCP - 5Mbits/s
    * UDP - 8Mbits/s