How to develop/test network applications?

[potto216]

I am working on an example to demonstrate using UDP in user applications in my forked repo. I am developing on a nRF52840dk and can display the 3 local IP interfaces setup in the board's kernel. But what is the best testing approach to get packet transmission working? My thought is to get the user application working by mocking the UDP driver with the Linux sockets. Once that is working then bring up the network stack on one nrf52840 with another nrf52840 running Zephyr’s IPv6 stack to use as the test source. Any thoughts on what the best development/testing strategy is for getting a an application that can demonstrate the basic capabilities of UDP?

[hudson-ayers]

I would start by testing interaction with the libtock-c UDP apps -- Flash the udp_rx libtock-c app on one board and see if your rust UDP app can send packets to it, and vice versa using the udp_send libtock-c app

[potto216]

Okay I'll first verify I have everything set up by having both boards communicate over UDP with libtock-c. Then I'll try the UDP libtock-rs app on one of the boards.
Thinking long term, it is going to be slow to have to test user apps by burning flash each iteration. How difficult would it be to:

1. Get the libtock-rs apps running on tockos in QEMU? It seems from the TockOS docs this solution is not mature.
2. Run the libtock-rs apps in RAM? Would this be as simple as changing the memory map.

[hudson-ayers]

I don't think that testing wireless protocols (i.e. 802.15.4) in QEMU is particularly practical, your QEMU setup does not have a hardware radio attached. Testing just the UDP portion might be possible using ethernet as the link layer (tock/tock#3110) but would require you to modify your UDP apps to target a TAP network interface as I think that is the only userspace interface that is likely to be exposed for ethernet for some time. And this would mean testing some substantially different code than you would have running on your nrf52840.

What is the motivation to run libtock-rs apps in RAM on your board? My experience with the nrf52840 has been that flashing apps takes only a few seconds, I don't expect that flashing RAM instead would lead to a meaningful speedup across iterations.

[potto216]

I like your idea about the TAP network interface as a long term solution. That would allow a mesh to be easily tested, like Openthread's simulator. Since TAP is layer 2 shouldn't 6loWPAN also be able to be pushed across it?

It was taking longer for me to flash an app on the nrf52840, about 1/2 a minute. But maybe I can speed something up on my system. however a bigger concern is erase life which is a maximum of 10,000 cycles. Since only one application can be loaded at a time and if it is combined with automated testing then compiling and flashing 40 times a day is not unrealistic. This means a board would have a life of about a year. But since this is a hobby, flashing isn't a big deal, but it would be nice to have an alternative:).

[hudson-ayers]

The TAP interface is primarily @lschuermann 's work, I am not that familiar with it. 6LoWPAN unfortunately has some cross-layer dependencies (e.g. UDP checksum elision requires knowledge of the specific link-layer checks used as an alternative) which make using 6LoWPAN on top of an arbitrary link layer a bit complicated. Also, IIRC the Tock 6LoWPAN stack also has some cross-layer dependencies of its own that would need to be refactored. Also, most of the IP stack for 6LoWPAN is in the kernel, while leon's work focuses on using LWIP in userspace. This is all just to say that any solution along these lines is definitely a significant effort, not to say that I wouldn't be interested in something along those lines.

Re: flash wear, Tock does have a mechanism which allows for flashing all applications at once as a bundle (tockloaders --bundle-apps) which would help some. Running apps out of RAM would probably be possible with some effort -- mostly reconfiguring the linker script and MPU configuration, I expect

[potto216]

Just as a follow up. I was able to install the libtock-c app libtock-c/examples/tests/udp/udp_send and it successfully transmitted UDP packets over 802.15.4 on the nRF52840 development board.