Tuesday, December 8, 2020

Ubuntu on Metabox (Clevo) L140MU

The Clevo L140MU uses the Intel 11th Gen i5 or i7 processor, which is an integrated SoC with wifi and Iris Xe graphics. The model I tested on has an extra 8GB of RAM, making 16GB in total, and a 512GB SSD. I chose the i5 model as the i7 is only 20% faster for a lot more money, and probably runs hotter. Both processors have 4 cores with hyperthreading. It comes with no operating system, so you don't have to pay the "Microsoft tax" -- a positive point for a Linux enthusiast. However, you can't buy direct from Clevo. You have to go to a reseller like Metabox, Sager or System76. (Their Lemur Pro seems to be this model.)

Physical characteristics

The laptop is extraordinarily light. The body is reportedly a magnesium alloy anodysed black. It's thicker than I was led to believe. It measures 15mm x 220mm x 323mm, excluding the rubber feet, which protrude a further 2mm. The base is not tapered and hence is fairly chunky for such a light laptop. This is to accomodate the 73 Wh battery. The build quality is good. The lid is mounted via a spindle-type hinge as on a Macbook, and looks really solid. It is very smooth, doesn't creak and goes back evenly with the same force all the way to 180 degrees as advertised. The lid is rigid, the screen is matte. The power cable goes in on the left hand side. The power brick is a fairly hefty 65 watt one. Ports on the left are thunderbolt, USB, HDMI and on the right, lock, USB, stereo audio jack, SD mini and power button. Ventilation is between the screen and the body. The fan is off or inaudible most of the time in normal use. When it does come on it is quiet and discreet.

The base has 12 screws deeply inset, and four rubber feet which seem firmly attached (so far) and are rather sharp. This is always a weak point with laptops and I remain sceptical that this new design will fare any better than usual. But let's hope I'm wrong.

The laptop comes with numerous ugly stickers, which have to be removed carefully without scratching the anodysed magnesium. I used a plastic spudger to lever up a corner and then pulled them off easily. You really don't want to use any kind of metal tool. And do it soon, before the glue sets hard.


The screen has a good range of brightness and although I can't measure it, it looks decently bright at full blast. It is of good quality and can be viewed at a sharp angle without dimming. Though they don't say it is IPS it looks like it is. It measures oddly 310mm x 175mm. This is a lot wider than your average 14 inch. However, a quick calculation reveals that this ratio: 1.77:1 is precisely that of FHD (1920x1080), so the proportions of all images displayed on it are true to life.

Keyboard and trackpad

The keyboard is a chiclet style with more than average travel. It is comfortable to use, though I wonder if too much of a gap has been left between keys and the surrounds for crumbs, fingernails and general rubbish to creep in. It has several intensities of backlighting reached by repeatedly hitting the keyboard backlight (fn-F4) key.

PgUp and PgDn are stupidly squeezed in above the left-arrow and right-arrow keys. This means that navigating via left or right arrow in a document frequently results in hitting PgUp or PgDn by mistake. The only way to make the left and right arrow keys usable is to disable PgUp and PgDn via xmodmap:

xmodmap -e 'keycode 117='
xmodmap -e 'keycode 112='

Making this permanent though may take a little more thought.

The trackpad is Elantec and as in my previous Clevo works well under Ubuntu. Two-fingered scroll works only in the "natural" way regardless of the setting in the Mouse and Touchpad control panel. To turn it off you need to type in the terminal:

gsettings set org.gnome.desktop.peripherals.touchpad natural-scroll false

The tapping areas need configuring as the default setting recognises the middle of the trackpad as the middle button of a mouse. This is easily fixed though:

sudo apt-get install xinput
xinput --list
xinput get-button-map 12
xinput set-button-map 12 1 1 3 4 5 6 7

The list command tells you the ID of the trackpad, which in my case is 12. The last command modifies the buttton-map for id 12 so that buttons 1 and 2 both do the job of button 1. I haven't yet managed to get this to persist between reboots, however.


Another drawback with this model is the poor sound quality of its speakers. Maybe I am spoiled from having higher quality speakers found in mainstream laptops, but there is a definite reverberation between the speakers and the keyboard. You really need to use headphones to get decent sound.


After 12 hours of normal use including rest periods it went from 100% to 40%. It lost about 12% overnight while in suspend (I think).

Installing Ubuntu

For this model you need Ubuntu 20.10 with the 5.8 kernel. With 20.04 (kernel 5.4) the brightness controls didn't work. Installation was easy once you find out that the F7 key lets you choose the startup disk. The wifi works fine. The backlit keyboard button (fn-F4) works, as do volume controls (fn-F5 and F6), brightness (fn-F8 and F9). fn-F1 does nothing. fn-F2 and F3 work as expected. fn-F10 does nothing. fn-F11 enters airplane mode. fn-F12 puts the screen to sleep.

After a while I realised that having to hold down the fn-key when accessing things like screen brightness is really annoying. So I reprogrammed the F3, F5, F6, F8 and F9 keys to control sound and brightness directly. For this you need to install xdotool and program the keys via Settings->Keyboard shortcuts. For example I defined a custom shortcut called "mute" with the definition xdotool key XF86AudioMute.

One issue that only emerged after using it for a while was that auto-suspend, which kicked in every 5 minutes of idleness, tended to crash the machine. I upgraded the software using Software Update and also disabled auto-suspend and now all seems fine.


This is a good laptop for Linux, especially as it does not come preinstalled with Windows. The build quality and the battery are both positive points. In spite of a number of glitches, which can all be got around. I would recommend this laptop for Linux. Remember there are no perfect Linux machines out there.

Thursday, August 27, 2020

async and await in a nutshell

The async and await keywords introduced in Ecmascript 2017 are significant improvements on the way asynchronous functions in Javascript have been called in the past, and are now supported in all major browsers, and in Node.js. Unfortunately, most explanations on the Web are marred by unnecessary detail. For the benefit of other confused readers I will try to explain the underlying concepts in the simplest possible terms.

Javascript functions come in two basic flavours: asynchronous and synchronous. Asynchronous functions execute when the time is right, whereas synchronous functions execute straightaway. Asynchronous functions give Javascript its power by maximising the usage of the CPU instead of blocking while network and other in/out operations complete.

The async and await keywords simplify the calling of asynchronous functions, which can now be declared with the async keyword. This can be applied to a simple function, a method in a class or a static class method:

async function foo(){ return 1;}
class bar { async foo(){ return 1;} }
class bar { static async foo(){ return 1;} }

When called, these functions or methods will yield the CPU to other pending functions rather than execute immediately. The await keyword lets you treat asynchronous functions as if they were synchronous. That is, you don't have to obscure the clarity of your program with callbacks, explicit promises or then-clauses to get things done. (Hallelujah!) Here's a simple example that uses async/await in a loop:

async function bar() {
   return 2;
async function foo(){
    let arr = Array();
    let total = 0;
    for ( let i=0;i<arr.length;i++ ) {
        if ( i == 1 )
            total += await bar();
            total += arr[i];

This adds up a list of numbers: 1, 7 and 3, whose total should be 11. But when it tries to add the second element of the array it gets it instead from the asynchronous bar() function, which returns 2 rather than 7. The program can be written as if it were synchronous because that call to bar() is prefixed by the await keyword. In effect, the code pauses at that point until bar() completes, before executing the next step in the loop. So the answer is 6, not 11.

However, you can only use await inside a function declared with async. Also, if you call an async function inside a synchronous function, or at the top level, the next step will execute immediately and not wait for the async function to complete. In the above example the final call to foo() is from the synchronous top-level, but it doesn't matter because this is the last statement in the program.

And finally, many functions defined in frameworks are already asynchronous. You can also call these using the await keyword. For example in jQuery you can use await with $.get, as long as you call it within a function declared with async:

let data = await $.get(url);
// do something with data...

So you don't have to worry about callbacks, and that's cool.

Tuesday, April 14, 2020

Converting UTF-8 and UTF-16 arrays to strings in Javascript and vice versa

Support for UTF-8 and UTF-16 conversion is not that great in Javascript. There are libraries for Node.js, like StringDecoder, but you have to require them. And in the browser they won't work. For browser Javascript you can use TextEncoder but it doesn't work in all browsers consistently and only in Node.js via the util module. So if you want (like me) something that can convert UTF-8 byte arrays and UTF-16 character arrays into strings and vice versa, and have exactly the same code work in both Node.js and in browsers with no dependencies you might begin to understand my problem.

A few people recommend using unescape(encodeURIComponent(s)) to encode utf-8 and decodeURIComponent(escape(s)) to decode, but both escape and unescape are deprecated. Also this method only produces strings, not Uint8Arrays and doesn't handle the UTF-16 case. Why would you need an array of UTF-8 bytes or UTF-16 characters? Because char and byte arrays can be compared and indexed into more easily. Also files store string data in these formats, especially UTF-8. If only bits of your file are in UTF-8 then you have to convert the string parts piecemeal. There are probably other uses too, or else Uint8Array and Uint16Array wouldn't exist.


For UTF-8 conversion Javascript already has two functions that do most of the work: encodeURIComponent and decodeURIComponent. encodeURIComponent takes a string and escapes a few reserved characters and also ASCII codes greater than 127 into single byte escape sequences. So '%" becomes '%25' and 'ó' becomes '%C3%B3'. This method also works on Unicode characters outside the Basic MultiLingual plane, for example the gothic character Hwair: 𐍈, which is escaped to '%F0%90%BD%88'. Once we have the escaped sequence it is fairly easy to take each byte and encode it as a 8-bit integer within a Uint8Array. The reverse process (Uint8Array to string) is also simple: any byte less than 128 can be converted back into a character using String.fromCodePoint(n), where n is the 8-bit value. For code points from 128-255 they can be converted back into their escape string form. Then the string built up this way can be passed through decodeURIComponent to produce the original string.


UTF-16 is even easier since all Javascript strings are already encoded in UTF-16. To convert a string to an array we can use str.charCodeAt(index), where str is our string and index is the index into the string. If the character is longer than a 16-bit integer it will be encoded as a 'surrogate pair', but it will still be extracted by charCodeAt as two 16-bit integers. Indeed, the length of the string in that latter case is the number of UTF-16 characters, not the length of the Unicode string, which will be shorter, because each surrogate pair is only 1 character. To reverse the process we can use String.fromCharCode, which converts each half of the surrogate pair separately and the character is put back together by the browser.

Here's my code. For Node.js just trim it to the class definition and add module.exports=unicode. This way you can test it in the browser easily.

<!DOCTYPE html> 
 * A simple class to convert utf8 or utf16 byte arrays to strings etc
 * Works in Node.js OR in any browser. No dependencies.
class unicode {
     * Convert a Uint8Array in UTF-8 to a Javascript string
     * @param uint8_array a Uint8Array in UTF-8
     * @return a Javascript string encoded in standard UTF-16
    static utf8_to_string(uint8_array) {
        var str = "";
        for ( var i=0;i<uint8_array.byteLength;i++ ) {
            if ( uint8_array[i] < 128 )
                str += String.fromCodePoint(uint8_array[i]);
                str += '%'+uint8_array[i].toString(16);
        return decodeURIComponent(str);
     * Convert a javascript string to Uint8Array UTF-8. 
     * @param str the string to convert
     * @return a Uint8Array in UTF-8
    static string_to_utf8(str) {
        var encoded = encodeURIComponent(str);
        // NB % sign itself encoded as %25
        var bytes = Array();
        var state = 0;
        for ( var i=0;i<encoded.length;i++ ) {
            switch ( state ) {
                case 0:    // convert characters to bytes
                    if ( encoded[i] == '%' )
                        state = 1;
                case 1:    // seen '%'
                    state = 2;
                case 2:    // seen %H
                    state = 0;
        return new Uint8Array(bytes);
     * Convert a javascript string to Uint16Array UTF-16. 
     * @param str the string to convert
     * @return a Uint16Array in UTF-16
    static string_to_utf16(str) {
        var arr = new Uint16Array(str.length);
        for ( var i=0;i<str.length;i++ ) 
            arr[i] = str.charCodeAt(i);
        return arr;
     * Convert a Uint16Array in UTF-16 to a Javascript string
     * @param uint16_array a Uint16Array in utf-16
     * @return a Javascript string
    static utf16_to_string(uint16_array) {
        var str = "";
        for ( var i=0;i<uint16_array.length;i++ ) 
            str += String.fromCharCode(uint16_array[i]);
        return str;
function test() {
    var u8_arr = unicode.string_to_utf8("dógs lov€ 𤭢s");
    var str = unicode.utf8_to_string(u8_arr);
    console.log(("dógs lov€ 𤭢s"==str)?"utf-8 test passed":"utf-8 test failed");
    var u16_arr = unicode.string_to_utf16("dógs lov€ 𤭢s");
    str = unicode.utf16_to_string(u16_arr);
    console.log(("dógs lov€ 𤭢s"==str)?"utf-16 test passed":"utf-16 test failed");
<p><input type="button" value="test" onclick="test()"> (read result in console)</p>