freebsd stable - Aug 2018 - FreeBSD blocks on BOCHS serial port

13.08.2018 20:52, Alexander Lochmann wrote:
> Hi folks!
> 
> We are doing some automatic experiments using FreeBSD running in a
> virtual machine.
> To control the experiment from the outside, we use serial ports to
> communicate with an userspace program.
> The communication via serial does work with QEMU. However, it does not
> work with BOCHS which is our desired emulator.
> Even simple operations like 'echo FOO | tee /dev/ttyu1' or 'cat
> /dev/ttyu1' do not work. Both commands block 'forever'.
> It does not matter whether we use ttyu0 (file backend) or ttyu1 (tcp
> socket).
> I put some debug output in sys/dev/uart/uart_dev_ns8250.c. The output
> suggests that the driver more or less reads and writes to the serial
> ports. At least it does something...
> 
> Do you have any hints how we can further analyze this problem?
> Did anyone came across a similar problem?
This could be modem control line "Carrier Detection" (CD) or flow
control problem:
emulators can have distinct default settings for serial ports.

You should not rely on defaults and make sure you disable modem control/CD
either explicitly (using stty(1) etc.) or implicitly by switching to /dev/cuau0
instead of /dev/ttyu0. Flow control settings should match too, for both sides
of virtual port.

On 13.08.2018 21:36, Eugene Grosbein wrote:
> 13.08.2018 20:52, Alexander Lochmann wrote:
> 
>> Hi folks!
>>
>> We are doing some automatic experiments using FreeBSD running in a
>> virtual machine.
>> To control the experiment from the outside, we use serial ports to
>> communicate with an userspace program.
>> The communication via serial does work with QEMU. However, it does not
>> work with BOCHS which is our desired emulator.
>> Even simple operations like 'echo FOO | tee /dev/ttyu1' or
'cat
>> /dev/ttyu1' do not work. Both commands block 'forever'.
>> It does not matter whether we use ttyu0 (file backend) or ttyu1 (tcp
>> socket).
>> I put some debug output in sys/dev/uart/uart_dev_ns8250.c. The output
>> suggests that the driver more or less reads and writes to the serial
>> ports. At least it does something...
>>
>> Do you have any hints how we can further analyze this problem?
>> Did anyone came across a similar problem?
> 
> This could be modem control line "Carrier Detection" (CD) or flow
control problem:
> emulators can have distinct default settings for serial ports.
> 
> You should not rely on defaults and make sure you disable modem control/CD
> either explicitly (using stty(1) etc.) or implicitly by switching to
/dev/cuau0
> instead of /dev/ttyu0. Flow control settings should match too, for both
sides
> of virtual port.
Thx. I cannot even run 'stty < /dev/ttyu1' to see the current
settings.
It simply blocks...

'stty < /dev/ttyu0' works perfectly. ttyu0 uses a file-based backend.
Whereas ttyu1 uses a tcp server-based backend with a connected
netcat.
> 
> 
-- 
Technische Universit?t Dortmund
Alexander Lochmann                PGP key: 0xBC3EF6FD
Otto-Hahn-Str. 16                 phone:  +49.231.7556141
D-44227 Dortmund                  fax:    +49.231.7556116
http://ess.cs.tu-dortmund.de/Staff/al

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