getchar() hangs in RELEASE compiling mod, not in DEBUG compiling mode

[martinkooij]

In my repo https://github.com/martinkooij/pi-pico-getchar there is a short bit of code showing a program that hangs when entering characters via getchar().

The use of this call causes the pico to hang at random, but mostly before having entered 10 characters. This happens when compiled in RELEASE mode.

• When using the -DCMAKE_BUILD_TYPE=Debug flag in CMake it does work flawlessly.
• When explicitly using a tight loop with getchar_timeout_us(0) it also works without problem.

[lurch]

Looking at getchar I see that it uses at_the_end_of_time, and I remember there being some problem with that a while ago... #145 or #255

Is your pico-sdk up to date?

[martinkooij]

Ahhh. Alas, I cloned a fresh pico-sdk this weekend (24 April 2021) on one computer and updated the one on the oher computer just over a week ago. I didn't check on any older versions. Both (windows) computers created the same executable, with the same problems.

[kilograham]

could not repro; pls attach a UF2 (and the .DIS file)

[martinkooij]

zipper.zip
Didn't reproduce either anymore. Don't know why. But was able to reproduce surefire with a somewhat more complicated example. Attached that one, cmakefile, .cpp files and the resulting DIS and UF2 at my computer. Fails at first try here with getchar(). Works with mygetchar().. Hope that helps, thanks for looking into it.

[kilograham]

Didn't reproduce either anymore. Don't know why. But was able to reproduce surefire with a somewhat more complicated example.
Yeah, one part of the problem was that the linker was getting to pick between two different implementations of getchar arbitrarily, however there was an actual bug beyond that.

I assume you are using gcc 10 as I couldn't repro it on anything earlier.

[martinkooij]

Yes, gcc 10.2 here.

[kilograham]

merged