Adding a new network interface

[obdevel]

I've recently become interested in SPE (Single Pair Ethernet aka 10BASE-T1S). Microchip is promoting it heavily as a replacement for CAN and RS485, and Arduino has a shield that supports the Uno R4. It interests me because it provides for 10Mb/s data transfer over a multi-drop bus using just single shielded twisted pair cabling. No bulky connectors, no ethernet switches, etc. There are many use cases where wifi isn't reliable or even available.

The current Arduino library is based on the reference driver code for the LAN8651 chip provided by Microchip but currently supports UDP/IP only (over the Arduino lwIP implementation).

I'd like to investigate adding support to this core. The R4 Arduinos aren't really powerful enough to take advantage of this, either to produce/consume 10Mb/s or to make use of the data (e.g. audio). And I'd like to have TCP/IP as well.

It seems that most of the parts are already in place, although glueing and shimming the bits together will be an interesting challenge.

Any advice ? Which existing ethernet interface library would you start from ? Any previous discussions to read ?

[JAndrassy]

the https://github.com/arduino-libraries/Arduino_10BASE_T1S library incorporates LwIP library and implements a network interface on top and base of LwIP. so I guess the task is to migrate the network interface implementation to work with LwIP in this core.

[earlephilhower]

Another Arduino library where they mix and match OSI levels. 😭. I understand why you have to do it sometimes too for in a tiny controller, but if you have enough CPU resources to run LWIP, you have enough resources to do it right.

All we need here is the world's dumbest NIC. We wrap things in the LwipIntfDev template and that implements the logic specific to this core.

If you look at the lwip_encj280 directory you'll find the general structure. There's by convention a utility folder which implements a class for the hardware interface, and a top-level include that defines the template using.

The hardware class implements maybe 6 methods to init/deinit the HW, send or receive a packet, and report physical layer 2 link state. Once that's hooked up everything "just works" since the template takes care of keeping things aligned with for needs.

If you can pull out those functions from the Microchip library, you're set.

[earlephilhower]

Oh, and to be clear, if the Ethernet driver ever calls an LWIP API, there is a problem. They are expected to only run Ethernet layer packet transmit/receive.

[obdevel]

Thanks for the pointers. I'll start with the Microchip driver, document its API and compare that against the ENCJ280. I'm pleased that this work can be isolated in a library and won't require any changes in the arduino-pico core.

I had to rewrite the CAN bus library for these R4 boards, so I'm no stranger to poking around in the internals.

I haven't looked at the memory footprint of the Arduino driver. They only have 32K of SRAM to play with on the R4 devices, which may also explain the absence of TCP.

[earlephilhower]

Actually, it may not be all that bad. If you ignore the Arduino-10bt library and go directly to the HW abstraction library you might get going faster. They seem to have ported to multiple MCUs (non-arduino) already. https://github.com/MicrochipTech/oa-tc6-lib

[obdevel]

Thanks. I'm waiting for hardware so I'll report back once I've had an opportunity to try out these ideas.