add serialport support to defmt-print

[brandonros]

I got the idea from https://github.com/gauteh/defmt-serial/blob/main/example-pi-pico/pico-elf2uf2-defmt-wrapper.sh except that didn't work for me on Mac OS X Ventura with a FT232RL USB device

Instead of trying to really get into the weeds and debug why that was doing nothing, this seemed easier.

Obviously we'd probably want this behind some feature flag to make this optional (or not at all)

Just figured this might help somebody developing on RP2040 who doesn't have a 2nd RP2040 laying around + doesn't feel like soldering wires to be able to hit the SWD RTT debugger thingie

[Urhengulas]

Hi @brandonros, thank you for your PR.

I'd be happy to add the serial support. Just a few questions:

1. Can you please share an example of how you use the feature? Just want to understand it better.
2. The library you are introducing, serialport, seems to look for new maintainers. I am a bit hesitant to add a library which has no active maintainers. Do you know if the found someone already?

[brandonros]

Hi @brandonros, thank you for your PR.

I'd be happy to add the serial support. Just a few questions:

1. Can you please share an example of how you use the feature? Just want to understand it better.
2. The library you are introducing, serialport, seems to look for new maintainers. I am a bit hesitant to add a library which has no active maintainers. Do you know if the found someone already?

If you are working on a RP2040 and you don't want to solder/attach a 2nd USB thing to handle defmt logs over SWD, you can do

.cargo/config.toml

[build]
target = "thumbv6m-none-eabi"

[target.thumbv6m-none-eabi]
runner = "bash runner.sh"
rustflags = [
  "-C", "link-arg=--nmagic",
  "-C", "link-arg=-Tlink.x",
  "-C", "link-arg=-Tlink-rp.x",
  "-C", "link-arg=-Tdefmt.x",
]

[env]
DEFMT_LOG = "debug"

runner.sh

#!/bin/bash

set -e

# flash
elf2uf2-rs -d "$1"

# debug uart
defmt-print -e "$1" serial --path /dev/tty.usbserial-A50285BI

combined with https://github.com/gauteh/defmt-serial to achieve "compile, flash, get logs" all in one command + not need an SWD debugger and instead just a typical USB -> UART

[brandonros]

I don't think CI / lint is failing due to something specifically related to this PR (other than adding a new serialport dependency)

[Urhengulas]

I don't think CI / lint is failing due to something specifically related to this PR (other than adding a new serialport dependency)

It fails because of the introduced dependency serialport. The relevant part of the error is:

could not find system library 'libudev' required by the 'libudev-sys' crate

By adding serialport you introduce following dependencies:

└── serialport v4.2.2
    ├── bitflags v1.3.2
    ├── cfg-if v1.0.0
    ├── libudev v0.3.0
    │   ├── libc v0.2.147
    │   └── libudev-sys v0.1.4
    │       └── libc v0.2.147
    │       [build-dependencies]
    │       └── pkg-config v0.3.27
    ├── nix v0.26.2
    │   ├── bitflags v1.3.2
    │   ├── cfg-if v1.0.0
    │   ├── libc v0.2.147
    │   └── static_assertions v1.1.0
    └── scopeguard v1.2.0

You'd need to install libudev in the lint job in the CI. Similar to here:

defmt/.github/workflows/ci.yml

Line 32 in ca161bf

run: sudo apt-get update && sudo apt-get install libudev-dev libusb-1.0-0-dev

But still, I do not want to add an unmaintained dependency. Are there any alternative crates?