About nobreak in ser2net configure

[atline]

Hi, there,

I have a embed device which only with nobreak added in ser2net.yaml, then I can send break successfully, see labgrid-project/labgrid#1663

Though I made it work, but I can't really understand it. Would you please help me to understand it? Thanks.

[cminyard]

The "nobreak" option on the serialdev gensio turns off break at startup. It really should be named "disable_break_at_start", but that's kind of long.

I imagine that the break signal is enabled on the serial port at startup. By default ser2net/gensio leaves it alone; nobreak turns it off.

-corey

[atline]

Thanks @cminyard for the reply.

I'm not sure to understand "the break signal is enabled on the serial port at startup". What does that mean?

And after further trial, I find:

1. All CP210X usb-to-serial chips from the vendor Silicon Labs, we should configure nobreak to support send brk
2. All other chips, no matter set nobreak or not, it works well to support send brk.

But, if I directly use minicom or microcom to open the /dev/xxx, nothing needed from my side, they just by default support break send (thus support sysrq).

So, does that mean for minicom, they default somewhat add something similar to nobreak of gensio? As from user's point, no obvious command difference to operate CP210x chip and non CP210x chip.

Finally, any side effect if I configure nobreak for these non CP210x chip too?

[cminyard]

I'm not sure to understand "the break signal is enabled on the serial port at startup". What does that mean?

Break is something that can be on or off, and just closing the port won't change the setting ( I don't think; I'm not 100% sure). "send brk" does a kernel operation that causes break to be sent for a little bit. If it's already set on, it will have no effect.

However, I'm not sure about this. If break was enabled, you wouldn't be able to type characters, and I assume that's working.

I looked at the Linux driver and didn't see anything unusual around break. It may be a bug in the hardware or firmware, like the first break setting doesn't do anything. I'm not sure.

So, does that mean for minicom, they default somewhat add something similar to nobreak of gensio? As from user's point, no obvious command difference to operate CP210x chip and non CP210x chip.

It may be that minicom turns off break at startup by default. If wouldn't be a terribly bad thing to do. ser2net tries to do as little as possible to the port at startup to avoid "glitching" things or changing state.

Finally, any side effect if I configure nobreak for these non CP210x chip too?

Besides turning break off if it's on, no other side effects.