[BRLTTY] Focus 1 70 display and USB to serial adapter: possible connecting this scenario?

[Hammer Attila]

Hi Dave,


Thanks your answers, I trying increasing the delay time and repeat the 
tests with -d serial:ttyACM0, and serial:ttyACM0+baud=57600 parameters.

The optional brltty.conf delay time parameter is good idea if you would 
like adding this option, because the baud rate possible adding the 
serial device with +baud=any correct baud number prefix.

Longer hard coded delay time value perhaps will be good this usb serial 
adapter, but need I think examining for example what happening if for 
example the usb serial adapter need 2000 MS delay time to correct set 
the baud rate if need perhaps appliing the +baud=57600 prefix (the 
purpose is BRLTTY always correct starting), but for example a general 
serial adapter perhaps will be too high this delay with future user 
experience.

Although, if I calculate correctly, 2000 MS is actually 2 seconds, e.g. 
20000 MS would be a very long delay for the user experience if immediate 
Braille output is needed e.g. on a recovery screen (20 seconds for 
BRLTTY to initialize the display, set the correct baud rate and start), 
the values ​​2000 MS and 20000 MS are only assumptions for an immediate 
serial connection, a value of 20000 MS will probably not be needed, e.g. 
the 2 second wait time while BRLTTY initializes does not seem like much 
compared to the other boot processes, I hope a smaller value will be 
enough based on experience. (hopefully).
So, it might really be best in the future if this value could also be 
controlled by a configuration setting, e.g. with the setting name 
serial_ready_delay.
The default setting could be the value that BRLTTY currently uses for a 
traditional serial port communication without the waittime patch (e.g. 
for the /dev/ttyS0 device), I don't know what this exact numerical value 
is, but I'm sure you know.
We'll see what my tests show with different values ​​and different 
variations.
I can't promise the results for today, it depends on how long I can play 
through the different possible variations (I want to test multiple 
starts and automatic starts just to be safe), but I'll definitely report 
back.
By the way:
I start the BRLTTY Braille display manager with a Systemd service, I 
probably have -q and --no-daemon specified in the /etc/default/brltty 
file on my Debian 12 system.
Do I need to adjust the systemd service file, or is the original version 
good?

Attila

2024. 12. 30. 18:16 keltezéssel, Dave Mielke írta:
> [quoted lines by Hammer Attila on 2024/12/30 at 17:53 +0100]
>
>> I think the 1000 or 2000 MS perhaps will be too long wait time. What do you
>> think?
> I'd still like to know how high it needs to be to work reliably without hard-coding the baud.
>
>> If you thinking need more increasing the wait time with larger value from 500
>> Ms, I will be repeat the test.
> Yes, I'd appreciate that testing.
>
>> So, BRLTTY is more time right starting this USB adapter when I using the -d
>> ttyACM0+baud=57600 option.
> I think that's because there's a longer delay since that sets the 57600 baud a little bit earlier.
>
>> Normal -d ttyACM0, or -d /dev/ttyACM0 newer automatically changing the baud
>> rate in adapter side this usb serial adapter my experiences.
> There are four variants that all mean the very same thing:
>
>     serial:ttyACM0, serial:/dev/ttyACM0, ttyACM0, /dev/ttyACM0
>
> This is all for backward compatibility to when brltty only supported serial communication, i.e. the /dev/ absolute path prefix is optional and the serial: communiction method is optional. The correct syntax is serial:ttyACM0.
>
> You asked earlier (but I forgot to quote it) if you can specify the baud parameter in brltty.conf - yes, you can. For example:
>
>     braille-device serial:ttyACM0+baud=57600
>
> Since the delay seems to need to be so high, I think I'll probably add another serial device parameter for that.
>
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