Category Archives: hardware

PC Engines APU2C4

Installing FreeBSD on PC Engines APU2

PC Engines APU2C4

The PC Engines APU2C low-power network computer on my desk, with serial console, the first ethernet port and a USB stick connected.

PC Engines has been producing small, low-power systems with AMD CPUs for a long time. Among the great features for building your own router are built-in serial console and multiple quality Ethernet controllers. For a project I selected the apu2c4, a system with three gigabit Ethernet ports and 4 GB of RAM. Together with a small M2 SSD module, you have a decently powerful machine to run as a router. In fact, it has enough capacity to run some applications as well, or even small VMs if you’re so inclined!

Installing FreeBSD

Installing FreeBSD on the APUs is fairly straightforward; however, a small number of gotchas might trip you up. Here’s how I managed to complete the install, and update the APU firmware once I had FreeBSD installed.

  1. Download the FreeBSD memstick installer image. I used my closest FreeBSD mirror to download FreeBSD-11.2-RELEASE-amd64-memstick.img.
  2. Copy the image to a USB stick that is at least as large as the image; 1 GB should be sufficient. I had trouble when I did the copying on my Mac with the resulting stick not working properly; using a FreeBSD box did the trick for me.
  3. Before booting from the USB stick, mount the UFS partition on a FreeBSD machine. For 11.2, that’s da0s2a; for other releases, it might be different. You can use gpart list to identify the UFS partition to mount.
  4. Add the following lines to /mnt/boot/loader.conf to properly enable just the serial console, and give the USB subsystem enough time to attach the USB stick:
  5. vfs.mountroot.timeout="10"
  6. Unmount /mnt and move the stick to the APU.
  7. Connect a serial terminal to the APU console port; I usually use an USB dongle and a null modem cable or adapter, and my own simple serial console program or cu(1), using 115200 baud.
  8. Boot from the USB stick and install FreeBSD as you would on any other PC. Before you reboot:
  9. Make sure to add the console and comconsole_speed variables to /boot/loader.conf on the installed system on the APU as well. Unless you add them, you won’t be able to log in to the console.

If you forget to edit /boot/loader.conf, not all is lost: you can change the settings during boot. But because the loader detects both the serial console and a keyboard (although the APU has no support for a keyboard or built-in graphics), it is somewhat cumbersome, as the console output will be screwed up.

Updating the BIOS

The APUs use CoreBoot as their BIOS. PC Engines has ready to use CoreBoot images on their own GitHub page. You can update the BIOS using flashrom, a command line tool to program firmware devices across many devices and platforms.

To update the APU BIOS:

  1. Download the correct CoreBoot image for your model of APU from, directly to the APU. I picked apu2 v4.8.0.1, which was the newest at the time of this post.
  2. Extract the firmware file:
  3. $ fetch
    apu2_v4.8.0.1.rom.tar.gz                      100% of  852 kB 4100 kBps 00m00s
    $ tar xf apu2_v4.8.0.1.rom.tar.gz 
    $ ls -l
    total 862
    -rw-r--r--  1 stb  wheel  8388608 Jun  8  2018 apu2_v4.8.0.1.rom
    -rw-r--r--  1 stb  wheel       52 Jun  8  2018 apu2_v4.8.0.1.rom.md5
    -rw-r--r--  1 stb  wheel   873087 Jun 26  2018 apu2_v4.8.0.1.rom.tar.gz
  4. Install the utility:
    $ sudo pkg install flashrom
    Updating FreeBSD repository catalogue...
    FreeBSD repository is up to date.
    All repositories are up to date.
    Checking integrity... done (0 conflicting)
    The following 1 package(s) will be affected (of 0 checked):
    New packages to be INSTALLED:
            flashrom: 1.0
    Number of packages to be installed: 1
    Proceed with this action? [y/N]: y
    [1/1] Installing flashrom-1.0...
    [1/1] Extracting flashrom-1.0: 100%
  5. Check that flashrom can talk to your motherboard OK:
  6. $ sudo flashrom -p internal
    flashrom v1.0 on FreeBSD 11.2-RELEASE (amd64)
    flashrom is free software, get the source code at
    Using clock_gettime for delay loops (clk_id: 4, resolution: 2ns).
    coreboot table found at 0xcfde9000.
    Found chipset "AMD FCH".
    Enabling flash write... OK.
    Found Winbond flash chip "W25Q64.V" (8192 kB, SPI) mapped at physical address 0x00000000ff800000.
    No operations were specified.
  7. Verify the version currently installed:
  8. $ sudo dmidecode -t bios
    # dmidecode 3.1
    Scanning /dev/mem for entry point.
    SMBIOS 2.7 present.
    Handle 0x0000, DMI type 0, 24 bytes
    BIOS Information
            Vendor: coreboot
            Version: v4.8.0.1
            Release Date: 20180608
            ROM Size: 8192 kB
                    PCI is supported
                    PC Card (PCMCIA) is supported
                    BIOS is upgradeable
                    Selectable boot is supported
                    ACPI is supported
                    Targeted content distribution is supported
            BIOS Revision: 4.0
            Firmware Revision: 0.0
  9. Program the new version to the flash chip:
  10. $ sudo flashrom -p internal -w apu2_v4.8.0.1.rom
  11. If flashrom complains about the image not matching the mainboard, you need to force the programming as suggested in this forum post.
  12. Reboot the APU to activate the new firmware.

(Astute readers will notice that the above output already shows version being installed; I took that output after successfully upgrading.)

I tried to update the BIOS using the procedure suggested by PC Engines, using TinyCore, but I had trouble creating a TinyCore USB stick. Luckily I came across this BSD Foren post and realised that I could just use FreeBSD directly.

Fixing the Wemos D1 Mini DHT22 Shield

The Wemos D1 Mini DHT shield V1 is a simple board that hooks up a DHT11 temperature and humidity sensor to the ESP8266. The data line from the sensor is connected to pin D4, which the ESP8266 uses during boot as a second TXD line. (This is why the LED flashes as you upload a new sketch: the LED is connected to D4.)

At least for the boards I’m using, this confuses the sensor completely, and it will not react to the ESP8266 trying to read data from it.

The only way to fix this then is to move the DHT22 data line to another pin. First, I cut the trace on the bottom of the PCB:

Cutting the trace between DHT22 and D4

This is how it looks like after the cut:

Trace between data line of the DHT22 and pin D4 is cut

Finally, I connected the data line from the DHT22 to pin D0:

DHT22 data line connected to D0

With the Arduino sketch adjusted to use pin D0 instead of D4, the sensor can now be read reliably.

p.s. It is possible that this problem is limited to clone boards that use the DHT22 instead of the DHT11. I now see that Wemos has discontinued the V1 version of this board. The current version uses a DHT12 sensor that communicates via I2C.

Booting from an USB disk – even when your system doesn’t support it

I like using VMware Fusion on my Mac, but it has one shortcoming: it cannot boot from USB devices. You can use disk images (floppy, CD/DVD and harddisk) as well as a physical optical drive, but USB devices are not available. That’s unfortunate if you want to use VMware to prepare a hard disk for a machine, and want to test booting off that system before installing it in the machine.

When I install a new FreeBSD machine, I often start out from an existing FreeBSD machine and install directly from that running system, instead of booting off an install DVD. Obviously, using a virtual machine for this bootstrapping system, together with a USB hard disk adapter, is very convenient. But without being able to boot the VM off that USB disk, testing can be cumbersome.

I was very happy to come across Plop, a boot manager with many features. The most interesting one for me is it’s support for booting off USB devices without BIOS support. Plop includes its own U/O/EHCI driver, supporting standard USB 1.1 and USB 2.0 devices and ports.

Also very important: Plop can be run off a CD or floppy image, so you don’t need to (re-)configure your main hard disk. If I feel adventurous, I might look into patching the Plop BIOS extension into VMware, making booting even easier. For the time being, I’m using the floppy image, since none of my virtual (nor physical) machines have floppy drives any more.

Also, when you have an older machine which BIOS does not support booting off USB devices, Plop might be very helpful!

TEMPer USB Thermometer

Measuring temperature in a PC should be easy: after all, most mainboards have extensive monitoring capabilities for temperature and voltage levels built-in. Unfortunately, very few of these facilities are documented properly, and software support is lacking. Instead of trying to navigate the maze that is lm-sensors (which isn’t even available for FreeBSD), I decided to look for some USB-based solution.

There’s a reasonably cheap chinese USB thermometer called TEMPer. I got mine from Brando for 12 Euros. It’s a USB-to-serial chip from WinChipHead. It’s DTR, RTS, and CTS lines are used to connect a LM75 I²C temperature sensor. To talk to the LM75, you need some bit-banging driver.

I’ve put together a command line utility for the TEMPer that can program the built-in thermostat (TEMPer has a LED connected to that output) and print out temperature measurement data. It does it’s job, and might serve as an example on how to do I²C over a simple interface.

Asus barebone Pundit4 P5G41 (with pics!)

We were in need of replacement hardware for our two Shuttle K45 we’re using as servers, since one of them developed a case of capacitor plague, and the Asus Pundit4 P5G41 turns out to be a nice choice. It’s compact, features a LGA 775 socket, two DDR2 sockets, space for one 3.5″ and one 5.25″ drive (SATA only), and even has a serial port built right into the case (we’re big fans of serial consoles).

This model seems to be relatively new (introduced apparently in the fall of ’09), and I couldn’t find any pics of the innards. I’ve added a couple of interior photos to our wiki. Enjoy!


Ein Neuseeländer hat sich dem Thema Raketenrucksack genähert. Nachdem er viele Nachteile beseitigt hatte (z.B. die kurze Flugzeit von ca. einer halben Minute), hat er neue Nachteile eingebaut: Gigantische Größe und fantastischen Lärm, immerhin aber garniert mit halbstündiger Flugdauer. Hier kann man sich das Spektakel ansehen:

Düsenrucksack – Bericht und Videos