No messages shown over serial/UART

[mckayb]

Apologies if this is a dumb question, or if there is a better place to ask these sorts of questions, but I copied and pasted the arduino uno serial example and successfully flashed it to my arduino uno, but I'm unable to see any of the "Hello from Arduino!" or the "Got {}" messages.

I'm on a mac and ran

screen /dev/tty.usbmodem144301 57600

But couldn't see any messages coming in while I was typing.

Is there an equivalent to the Serial.print with the normal C/C++ variant that Arduino uses?

Serial.begin(57600);
Serial.print("Some value");

When I run the same screen with something like that, I can at least see values coming in.

[Rahix]

Can you share more details what exactly you were doing? How did you build the example? How did you flash it?

[mckayb]

All the code is here:
https://github.com/mckayb/rust-arduino/tree/project/love-o-meter/rust-arduino-03-love-o-meter

I copied the src directly from:
https://github.com/Rahix/avr-hal/blob/master/boards/arduino-uno/examples/uno-serial.rs

To build it, I installed all of the avr tools, overrode rust to nightly, and just ran cargo build with the target set to the avr-atmega328p.json file listed in the code.

To flash it, I ran avrdude -q -patmega328p -carduino -P/dev/tty.usbmodem144301 -D -Uflash:w:"target/avr-atmega328p/debug/rust-arduino-03-love-o-meter.elf"

This was the output of both of those commands:

    Updating crates.io index
   Compiling rust-arduino-03-love-o-meter v0.1.0 (/Users/mckaybroderick/Code/rust-arduino/rust-arduino-03-love-o-meter)
    Finished dev [unoptimized + debuginfo] target(s) in 0.95s

avrdude: AVR device initialized and ready to accept instructions
avrdude: Device signature = 0x1e950f (probably m328p)
avrdude: reading input file "target/avr-atmega328p/debug/rust-arduino-03-love-o-meter.elf"
avrdude: input file target/avr-atmega328p/debug/rust-arduino-03-love-o-meter.elf auto detected as ELF
avrdude: writing flash (23882 bytes):
avrdude: 23882 bytes of flash written
avrdude: verifying flash memory against target/avr-atmega328p/debug/rust-arduino-03-love-o-meter.elf:
avrdude: load data flash data from input file target/avr-atmega328p/debug/rust-arduino-03-love-o-meter.elf:
avrdude: input file target/avr-atmega328p/debug/rust-arduino-03-love-o-meter.elf auto detected as ELF
avrdude: input file target/avr-atmega328p/debug/rust-arduino-03-love-o-meter.elf contains 23882 bytes
avrdude: reading on-chip flash data:
avrdude: verifying ...
avrdude: 23882 bytes of flash verified

avrdude: safemode: Fuses OK (E:00, H:00, L:00)

avrdude done.  Thank you.

Then when I ran screen /dev/tty.usbmodem144301 57600
I just see a blank screen. When I type, nothing happens.

Thanks for taking a look at this. Let me know if there's something else you need.

[Rahix]

Hmm, so you're building a debug build:

    Finished dev [unoptimized + debuginfo] target(s) in 0.95s

and looking into your Cargo.toml, I see you've configured the compile profiles as follows:

[profile.dev]
panic = "abort"

[profile.release]
panic = "abort"

This will produce a huge bloated binary because absolutely no optimizations are done (no inlining, dead code removal, constant folding, etc.). This means, it eats a lot of the available flash memory (23.3 KiB from your output above) but will also run very slowly. I could see this massively throwing off the timing for the USART peripheral and thus nothing is working. It could also run into a lot of other issues due to the missing optimizations.

I would recommend trying to configure the compiler to more aggresively optimize, in both debug and release builds. In step 5 of Starting your own project in avr-hal's README, the settings we recommend are these:

[profile.dev]
panic = "abort"
lto = true
opt-level = "s"

[profile.release]
panic = "abort"
codegen-units = 1
debug = true
lto = true
opt-level = "s"

I'd give those a try, maybe that is all that's needed to make it work :)

[mckayb]

Ha, turns out, that was all it was! Thank you so much!