What termios settings cause endpoint to get garbled serial?

I have two endpoints. One is Windows Subsystem for Linux (Ubuntu) and the other is a small AR9331 router (running OpenWRT and has 16550 chip). They are connected over a USB-to-Serial connection.

Sending from AR9331 to WSL works as expected.
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Sending from WSL to AR9331 does not work as expected, it appears garbled or out of order.
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AR9331 TTY settings:

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WSL TTY settings:
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I tried messing with canonical mode, but it did not appear to change anything.

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Author: user_ABCD

How to active the second console to a FreeBSD guest running in bhyve?


I’m running FreeBSD 12.1-RELEASE as a host for bhyve virtual machines.

I have a FreeBSD 12.1-RELEASE guest running inside a VM. I would like to have two TTY-class devices configured for it.

According to the manual page, in order to start the VM with two TTY-class devices I have to start bhyve with command-line options similar to those: -l com1,/dev/nmdm0B -l com2,/dev/nmdm1B. Then I should be able to connect to the guest via those two nullmodem terminals with cu -l /dev/nmdm0A and cu -l /dev/nmdm1A.


The first command works as expected: cu -l /dev/nmdm0A shows me the main console of the guest.

The second command, however, attaches to the guest, but shows nothing. I would expect to show me a login prompt as if switched to another TTY.

What am I missing?

Additional details

  • The guest is a fresh installation of FreeBSD.

  • The output of dmesg | grep uart on the guest is as follows:

    uart0: <16550 or compatible> port 0x3f8-0x3ff irq 4 flags 0x10 on acpi0          
    uart0: console (115200,n,8,1)                                                    
    uart1: <16550 or compatible> port 0x2f8-0x2ff irq 3 on acpi0
  • I’ve tried setting hint.uart.1.flags first to 0x10 and then to 0x80 (although this one is for kernel debuggers from what I understand from uart(4)) and rebooted after each change. It didn’t work.


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Author: Mateusz Piotrowski