Teclast F5 – Update

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Some time ago I wrote a review of my experiences with the Teclast F5 11.6″ slim laptop and Linux. I am still a fan of this low cost but super slim and light weight laptop. It offers everything I need as an ultra mobile laptop for travel – 8GB RAM, M.2 SATA SSD slot, full-HD display and even touch. It is really pretty nice for the price point, I bought it new in Hong Kong for IIRC 360 Hong Kong Dollar which translates into about 310 or 320 EUR. Absolutely worth it. Especially the 8GB are pretty rare in small and low cost laptops.

By now mainline Linux kernel 5.3.0 onward the out of the box experience is pretty good, nothing much is needed to get it to work with all peripherals, though I have to admit that I did not test pen input yet since I do not yet own such The T6 active stylus pen, I just ordered one from China and will report later if it works with Linux and how. I also tweaked together a /etc/rc.local to setup some power saving settings right after boot (download here <link>). What I still need to figure out is to overcome some shortcomings of the keyboard. First is there are not Page-Up/-Down, Pos1/End keys, which can be pretty annoying quickly. I would like to define these e.g. as ALT-<cursor key>. The keyboard us US-English layout, so I would also like to define German Umlauts in a more convenient way. ATM I use the caps-lock key as compose key but this is inconvenient. For me it would make more sense e.g. to use Alt-right as modifier and ALT-r + letter key (like ‘u’) to produce the matching the Umlaut ‘ü’. But with GNOME and Wayland this is not very straight forward.

Oh, and ne final minor annoyance is that the Realtek audio codec driver misses a quirk for the F5 that disables the speaker amplifier before putting the codec to sleep, which results in pretty loud click sounds every time the codec get dis- or enabled. Since these things are usually tied to GPIOs of the codecs and these can be custom controlled it is hard to figure out which GPIO is actually used in the F5 hardware as long as we do not have schematics. The other problem is that the Realtek ALC282 codec documentation is not publicly available, so one can not even easily determine how many GPIOs there are and which are suggested for such use cases. Once if I have enough time I try this by simple trial and error which means a lot of kernel building and rebooting, thus very time consuming.

But what I wanted to talk about today are two other topics, the real energy consumption of the F5 and about the new revised model Teclast released recently, the F5R. Battery first.

F5 – Real Energy Consumption

So, what I recognized pretty early after installing Linux was that the battery Watt draw gauge was a bit suspicious. If you start powertop when running from battery it will show you on its first screen some power statistic and in the first couple of lines also the current drain. The suspicious thing is that it basically always shows 3.85Watt on my laptop, this is what ACPI reports (you can also check /sys/class/power_supply/BAT0/power_now ). And this is regardless if the screen is super bright or not, if WiFi is enabled or not and even if the CPU is under load or not. So this can not be true. The estimated remaining battery time is calculated from this energy consumption so one has to assume this is also not correct. My laptop reports very optimistic readings of 8h or more of battery runtime, which would be awesome, but sadly is rather unrealistic.

Recently I got a pair of USB type-C power measurement dongles, you can buy them pretty cheaply for about 10EUR/$10 upward. Plugging in one of these between the laptop and the AC adapter it became obvious that the 3.85W are completely wrong. With medium screen brightness and CPU idle my system consumes about 5W, peaking up to 6W and something in small spikes when the CPU becomes active (or GPU updates).

Teclast F5 idle power consumption

Given the 29Wh battery (and assuming that at least this ACPI reading is correct) this results in a more realistic runtime of about 6h – with only light to no CPU load, the more you do the less run time you will get. But well, up to 6h is not that bad either especially taking into account that the device is really thin and leightweight, i.e. the battery can only be adequately small.

While talking about power sources, I wanted to have a secondary AC adapter too so that I have a spare and found that sourcing proper USB type-C AC adapters is a pretty painful thing. What you need for the F5 is an AC adapter compliant with USB type-C Power Delivery specification. I found that the F5 will not accept adapters that do not go up to 12 Volt DC. Power Delivery can negotiate the voltage and current between the charger and the charged device. The higher the current, the higher the voltage to reduce losses. The first adapter I bought advertised with “USB quick charge” and “PD compatible”. The “quick charger” thing is a slippery slope since it is not defined what this entails, often this mean proprietary USB negotiation protocols, especially Qualcomm and Mediatek have these. These will not work with the F5 (or any other PD compliant device). I also figured that many wall warts that offer a type-C port and a type-A port and advertise “quick charge” are often not PD compliant. I now made good experience with 18W type-C PD compliant wall warts that advertise to go up to 12V. A PD charger with only up to 9V will trigger the charging in the F5 but it will not charge, it will not even hold charge, the laptop will continue to drain the battery.

The F5R vs F5

Recently I saw that Teclast now offers a new version of the F5 – the F5R (maybe R like Revised). I thought oops, bought too early? So I looked at the updated specs. In turns out that pretty much nothing changed except for the CPU. The CPU in the F5 was the Intel Celeron N4100 (Geminilake), the F5R now has an Intel Celeron N3450 (Apollolake). Is this better?

No, it is not. The N3450 is a about one year older than the N4100. It is also made in a 14nm silicon process, but it contains older everything. The GPU is one generation older which also results in less supported video codecs for en- and decoding, the CPU has only half the L2 cache (which has a performance impact), the RAM interface is DDR3 instead of DDR4 (but it can do LPDDR4 and I don’t know if Teclast uses LPDDR in the F5) and the turbo maximum frequency is 200MHz less, a more complete comparison can be found here: https://ark.intel.com/content/www/us/en/ark/compare.html?productIds=95596,128983

So all in all a bad deal, why did they do it then?

Well, Intel had and in parts still has massive supply issue with some CPUs and I suspect that Teclast did not get enough N4100 from Intel in time to supply the demand for the F5. So if you interested in getting a F5 I would advise to try getting the “older” F5 and not the F5R, you will notice the difference.