refactor serial follow up (some reboot fix)

[GMagician]

Fix a divide by 0 issue that may cause boards reboot

[rhapsodyv]

It would be good to take a look in the serial methods code before the recent changes, as before we had no issues.

[X-Ryl669]

The problem described above was present previously but it never triggered.

In the new serial code, I've merged all Serial::print to a single place, and I've used AVR's print method as a base for this code. It seems that GMagician's compiler consider uint8_t as char so the overload of print based on char is called to print uint8_t numbers. Marlin's code is using uint8_t in some loop iterator, so, instead of printing the iterator value, it's printing the character with the iterator's value.

I'm not fond of the fix here, since it changes the behavior of the print code to pass the issue, but it'll break elsewhere where print(char) is actually expected. I have to think about a correct fix.

[X-Ryl669]

If you don't mind, I'll use your fix in my kill all serial bugs PR here: #20932, so you can close this one.

[GMagician]

If you don't mind, I'll use your fix in my kill all serial bugs PR here: #20932, so you can close this one.

It's ok to mee

[X-Ryl669]

Can you try the pushed fix in #20932 to see if it works ?

[GMagician]

Can you try the pushed fix in #20932 to see if it works ?

No it doesn't, it prints G29 T with chars and not with numbers
Edit: but solve reboot

[GMagician]

@X-Ryl669 I think that Marlin needs chars as signed otherwise when doing: SERIAL_ECHO(' ') and SERIAL_ECHO(i) (with i as uint8_t) should always print a letter and that's not what should do.
Some STM32 platforms force the signed chars and I think this should be default to all, I proposed a PR for this, let's see what @thinkyhead says on that

[X-Ryl669]

My error here. -fsigned-char is used with gcc for ARM, so yes, all platform use signed char on Marlin. Sorry for the noise.

[GMagician]

Wait...there are some parts in marlin that send uint8_t and needs a single byte... Things turn out to be harder

[X-Ryl669]

We'll continue discussion in the PR's thread, if you don't mind.

[GMagician]

We'll continue discussion in the PR's thread, if you don't mind.

Yep, Better