Silent 4K X-Terminal (Experience report)
We built two X-Terminal with 3840x2160 resolution. The first is based
on the following hardware (for the second, see below):
A few months later, the following Mini-ITX motherboard became available:
- The combination produces the full resolution at 30Hz with HDMI,
and at 60Hz with the provided DP-miniDP cable.
- After power loss, if only the DP-miniDP cable is connected, the
ZBOX beeps for four times and does not display anything on the screen
(it obviously wants to display on a different output; there is no
firmware option to change that), but reacts to keyboard input and
boots an OS if available. However, all OSs we tried (Windows 10
(which we tried), Ubuntu 16.04, and a Debian-based LTSP recognized
that the monitor was connected via DP and all give the full resolution
at 60Hz. Then, after rebooting without power loss, the firmware
displays on DP, too. So, the sequence to change firmware settings is:
Power on, boot an OS, then reboot into the firmware (no idea what
happens if you cannot boot the OS).
- Network (PXE) bootin of the Zbox did work with the (UEFI) settings
we tried initially. We finally got it to boot by switching to "Legacy
only", then "save and exit" from the firmware, then go into firmware
again to tell it to boot with PXE (from the network); you have to set
up the ability to boot with PXE in one of the earlier submenus of the
firmware, or you don't get this option in the Boot submenu.
- Once we could boot from the network, we tried the LTSP setup based
on Debian 8 (Jessie) with the 3.16 kernel that we also used for some
older Zbox-based X-Terminals, and much to my surprise, it works fine
in our tests up to now (I did not expect this old kernel and X server
to drive the Skylake's graphics at 4K correctly).
- The power consumption of the Zbox when idling is 10.7W (and 24VA).
The CPU heats up to about 50 degrees C (30 above the surroundings) at
this power consumption if the Zbox is standing flat on the table (as
apparently envisioned by the designers; there are only legs provided
for this position). I played a bit around with firmware options for
C-states and such things, resulting in saving 0.6W, but also in some
malfunction that made me revert to the original conservative settings.
The monitor uses 56W at full brightness and 40W at brightness setting
50 (which is not much less bright), which is very good for such a big
- Not working yet: When the screen saver turns the screen black (and
presumably turns off the video signal), the monitor turns on its
backlight every few seconds for a few seconds to tell me that it is
looking for input on HDMI1 and miniDP (if i have not locked the
input), or just on miniDP (if I have locked the input). I have not
found a way yet to tell it that "video off" means "standby". After
some playing around I used HDMI instead of DisplayPort; the downside
is that this provides only 30Hz for 4k, but for typical X-terminal
uses, that's not a big problem; it was noticable at the start, but I
soon got used to it.
J3455-ITX, again with 2x8GB DDR3L RAM (again, much less is
probably enough); we put this into an old Mini-ITX case.
This board includes a HDMI 2.0 port (using a
display-port->HDMI 2.0 converter chip) for 4k@60Hz. The other boards
available at the time of this writing, have only HDMI 1.4 (not
4K@60Hz) and neither DisplayPort nor HDMI 2.0. If you want a Barebone
PC (or a smaller PC than available in Mini-ITX format),
NUC Kit NUC6CAYH also supports HDMI 2.0, but you pay about twice
as much as for the board above plus a Mini-ITX case.
No Apollo Lake boards or barebones with an external DisplayPort are
available at the time of this writing.
We use this board with
U32E850R monitor described above.
- One nice advantage that the ASRock board has over the Zbox is
that it has PS/2 in addition to USB connectors, so I can use my old
keyboard without needing a PS/2-USB converter.
- When connected to port HDMI1 of the monitor, we got only 4k@30Hz.
We needed to connect to port HDMI2 to get 4k@60Hz.
- Linux kernels up to 4.7 introduce pauses of a few seconds,
sometimes every few seconds; Linux 4.8 and 4.9 do not have this
problem (tested both with Ubuntu 16.10 and the LTSP setup described in
the following). So we built a Debian Testing/Stretch-based LTSP by
first building a Debian Testing chroot setup, chrooting there,
building an LTSP setup with ltsp-build-client, and finally installing
it in the usual places. Earlier we tried using a backports kernel
with the jessie LTSP setup, but that did not work properly (in
particular, did not start X) due to some overlayfs incompatibility.
- The result works nicely for most applications; an exception is
Firefox/Iceweasel: edit fields often get the wrong background colour;
it's especially annoying if the wrong background colour is black, and
the foreground colour is also black. Update: The problem seems to
come from the (default) driver "modesetting"; adding a line
to .../etc/lts.conf made the X server use the Intel driver which fixed
this problem (and is probably also faster).
- Idle power consumption with our case is similar to the Zbox (I
expect that you can get power supplies that are better); the box does
not feel as warm, though, because it is larger.