The intention

I have a new shiny PC Engines APU (some sort of masterpiece among small and power-efficient server hardware), and the intention is to make it serve as a home Internet gateway and a provider of additional home services.

01 apu4d4 null modem db9m db9f usb macbook

I have the following things at my disposal:

  • (1) apu4d4 with DB9M socket for console access

  • (2) null-modem patch with DB9F sockets on both sides

  • (3) USB to RS-232 adapter cable with DB9M socket

  • (4) MacBook with USB 3.0 socket

And the task is to manage a connection between the MacBook as an operator console and the APU as a target host to operate. It’s required for initial APU boot configuration and OS installation. In the future, it may also be necessary for troubleshooting cases when the only way to control the APU host is through its built-in serial console port.

How-to notes

Well, everything is connected and APU is ready to fire up. It’s known that the USB - RS-232 adapter on the desk is based on FT232, and FreeBSD OS is capable of dealing with such hardware out of the box. My usual preference is to avoid altering or cluttering up macOS with third-party drivers for infrequent atypical use cases, for the sake of a higher chance of stability. Luckily, I have a FreeBSD 12.1 installed on a VirtualBox VM instance, let’s give it a try:

  • make sure that the VirtualBox VM is configured to provide USB capabilities:

02 virtualbox usb settings

  • boot the virtual machine, log in as root

  • make sure all the hardware parts are connected, except APU’s AC adapter

  • pass DB9M - USB converter into the virtual machine:

03 pass usb device into virtual machine

You should see the FreeBSD kernel talking about the new device attached:

04 kernel output upon usb device attachment

  • connect to the console with old good tools like this (APU specifies its serial console port with 115200 baud rate):

    # cu -s 115200 -l /dev/ttyU0

  • or connect with any other one which supports serial console:

    # pkg install screen
# screen /dev/ttyU0 115200

  • power up the APU (connect its AC adapter), and the BIOS prompt should pop up eventually:

05 seabios prompt

  • let’s try to run memtest by pressing F10 and 2:

06 apu memtest

That’s it, the required console connection is established — the further configuration and OS installation can proceed.

 
 

Copyright © Igor Ostapenko
(handmade content)