diary at Telent Netowrks

Just enough NixOS for Kodi#

Sat, 26 Jun 2021 21:56:17 +0000

I've had an Odroid C2 sitting under the TV for a a year or so, mostly used for playing the Shaun the Sheep videos that live on my PC upstairs. I put LibreELEC on it when I bought it, and subsequntly tweaked it in a succession of ways that I basically don't remember.

Quite recently I decided that I didn't need this pocket of divergence in my otherwise mostly congruent domestic computing infrastructure, so I set about installing NixOS on it. There's a description in the NixOS Wiki of how to do this which is a good starting point, but there was some other stuff I had to figure out.


I still don't have everything figured out. In particular, it seems to want to play audio slightly too fast, I think because somehow it has decided that my 48kHz sound device will accept 44.1kHz PCM without need of resampling. I probably won't update this blog entry when I figure that out, but I will update the repo it points to.

I would caution against following these notes from start to end and doing everything manually as I discovered it, because there's a configuration.nix at the end that has most of it automated.

Initial install

The board has some weird requirement to install a binary blob and an u-boot image in a very specific part of the storage medium. "Note this assumes u-boot is in partition 1 of your board's connected eMMC", say the instructions. I am happy to report that the same merry dance works just fine on an SD card if like me you were too stingy (or poor) to spring for the eMMC.

Kernel rebuild

Although the generic NixOS aarch64 kernel will work to get you to a login prompt, it doesn't work well for video playback. This is because there's a meson_vdec module needed for hardware video decoding that isn't in it. After some experimenting I came up with the following configuration snippet

  nixpkgs.overlays = [
    (self: super: {
      linuxPackages = super.linuxPackages_latest.extend (lpself: lpsuper: {
        kernel = super.linuxPackages_latest.kernel.override {
          extraConfig = ''
             STAGING y
             STAGING_MEDIA y
             VIDEO_MESON_VDEC m

but this is where I found that the machine is slow as molasses at compiling - although to be fair the default NixOS aarch64 kernel build is a huge task on any hardware due to the large number of modules it builds.

Hot cross bins

So, time to figure out how to cross-compile it on an x86_64, and given that I want this to be repeatable, how to cross-compile the entire system instead of cross-building bits and native-building other bits and copying artifacts around by hand. Like this, is the short answer (adjust pathnames/hostnames as needed)

 # build the system
 NIXOS_CONFIG=/home/dan/src/odroid/nixelec/configuration.nix \
  nix-build -E 'let pkgs = (import /home/dan/src/nixpkgs) {};
  in (pkgs.pkgsCross.aarch64-multiplatform.nixos

 # copy it to the target device
 nix-copy-closure --to root@odroid.lan -v --include-outputs \
   ./result && ssh root@odroid.lan \
   `readlink result`/bin/switch-to-configuration switch

As usual with cross-compilation, this unearthed a bunch of packages that don't cross-compile because nobody really understands when to use buildInputs vs nativeBuildInputs (I'm projecting here, it might just be me), one package that doesn't cross-compile because it's magic - I refer of course to gobject-introspection - and some packages that need their derivations tweaking so that they don't depend on any of the other stuff that depends transitively on gobject-introspection.

Image problems

Careful readers will observe that the shell incantations above are predicated on having a running NixOS Odroid system already that you can ssh into - so, how do you get that in the first place? I augmented the configuration further so that it can also be used to produce an SD card image which has builtin the faffage needed to get the firmware and U-boot binaries injected at the right offsets. To generate this, we do

NIXOS_CONFIG=/home/dan/src/odroid/nixelec/configuration.nix \
 nix-build -E 'let pkgs = (import /home/dan/src/nixpkgs) {};
  in (pkgs.pkgsCross.aarch64-multiplatform.nixos

(this is very similar to the previous command except now we're building sdImage instead of toplevel)

and then find the output in result/sd-image/nixos-sd-image-21.11pre-git-aarch64-linux.img - again, Your Pathnames May Vary. dd this to whatever device corresponds to the SD card you plan to insert into the Odroid machine and you should be good to go. It should install a valid SSH key for the root user, but it would be as well to check.

Where is it?


What's left to do?

What's up, D?#

Fri, 30 Apr 2021 17:27:22 +0000

One of the nice things about side projects (as opposed to the ones I get paid for) is not having to be accountable to anybody for timely delivery, and the freedom to head off on tangents or side investigations. I have recently picked up NixWRT again, but I regret to inform you that "off piste" is where I am right now.

Backstory: monit is not a great service monitor for my needs, mostly because it isn't the parent process of the service daemons it starts, so can't tell when they exit without polling/pid files etc - which is slow and unreliable. So I decided that the world does not have enough init replacements already, and because of the risk that anyone else might otherwise find it useful I decided to write it in Fennel. Then a little while later, I decided to do something else for about five months, and now I have no mental context of what I was doing.

So why not start again? This time it's called upd and although it shares some ideas with swarm, I am attempting to use tests to drive more of its design.

I started by sketching out the shape of a plausible service monitor for a pppoe daemon. You can see that the state logic is complicated and it has many collaborators, so I install mock versions of them by setting entries in the package.loaded table which require checks before loading a file. The most complicated bit is probably the fake event loop: the test setup provides an array my-events of functions which may update state, replace mocks etc, perform assertions etc, and and the mock event loop runs them one by one. This lets me write my first test, to see that the daemon is started when the interface is present. A followup refactor replaces the longwinded calls to tset package.loaded with more intention-revealing names mock and mocks.

The second test checks that we observe an exponential backoff when the process fails to start. We don't have any visibility into the actual backoff state in the system under test, so have to observe from the outside. First we stop the process from an event function, and then poll the process state repeatedly while incrementing a counter until it restarts. 0e966459

This is convoluted and might suggest that we should make that state visible. But it also prompted me to try making backoff state be a property of the process monitor itself, not the overall system under test - suppose we want to write a script that watches two or more processes? The next few commits

Of course, making the backoff state a property of the process has the side effect of making it visible. The next test is that the process is stopped if the underlying link is lost, and it's actually quite handy to be able to reset the backoff interval in the test setup: 0350c8aed6a

Something was still bothering me here, though. In order to move the backoff testing from the script to the process, I'd done

-      (when (and (not (process.running? pppd))
-                 (nil? pppd.backoff-until))
+      (when (not (process.running? pppd))

This is logically correct, as pppd:backoff does nothing anyway if pppd.backoff-until is nil. But it's really quite non-obvious. What we actually want to say here is "if the process died, back off" - so let's say it! Add a process.died? method and rewrite the test to use it.

The last interesting change in this sequence was triggered by looking at the event loop, when I realised that we don't anywhere use the value of the event that comes back from next-event - we wait for something to happen, but then we discern what happened by testing various bits of state. To say the same thing again in fewer words: we're don't receive events, we wait for state changes. So let's change the code to use better names

What's the conclusion? Is there a conclusion? A few thoughts -

First steps in Colemak#

Thu, 15 Apr 2021 14:29:26 +0000

This is more of a placeholder than anything else, but I decided at the weekend that it was time to learn to touchtype, and further, that it would make sense to switch to Colemak at the same time. I don't yet know if it actually will prove correct, it's too early too say.

I'm using Colemak Academy and have achieved 97% on the home keys at an astonishingly speedy 18 words per minute, but the top and bottom rows are still strangers to me. And only after trying to use Emacs did I learn that the Colemak layout rebound Caps lock (which I bind to Ctrl) as Backspace).

The ANT is my friend, it's blowing in the wind#

Sat, 06 Mar 2021 14:46:16 +0000

A few weeks ago I won some bike rollers on Ebay, and once I'd mastered the basic skills (pedalling without falling over, stopping without falling over, starting without falling over without holding onto the door jamb), I started looking for some way to measure what I was doing. Another Ebay purchase later and I was the owner of a Garmin GSC10 speed/cadence sensor. (There are two standards for wireless fitness equipment: ANT+, which is the older one, and probably obsolescent, and Bluetooth Low Energy, which is newer but is based on Bluetooth, therefore probably unreliable. Also, in terms of what I could find on Ebay, BTLE is double the price for any brand I'd heard of.)

But the sensor is only half of the solution: I also need something to display the values, and as I already have a handlebar mount for my phone I decided that an Android app would be the thing.

There is more than one route to persuading an Android phone to receive ANT readings: you can

Then I needed an app.

 As a cyclist
 I want speed and cadence displayed in big numbers
 So I can see them even when the wind is making my eyes water
   and the sun is shining on the phone display

Apps for ANT+ sensors also seem to be comparatively thin on the ground. IpBike seems to be the de facto standard, but after trying it a few times I was struck by acute NIH, and decided it would be more fun to write my own than to figure out whether I could configure it for my needs ...

Three weeks later I'm not sure it is more fun, but it's certainly a learning experience. https://github.com/telent/biscuit

Her name is Oreo#

Fri, 12 Feb 2021 13:47:14 +0000

I am at a point somewhere along the way of a long yak-shaving journey ("I wonder if the MSM8953 SoC supports ANT+ in hardare and it just needs enabling in the Android software?") which involves rebuilding Android for my phone. There seem to be very few ROMs for the Moto G5 Plus ("potter") that are still being maintained, and even fewer of them that have build instructions that (a) work as described; (b) comprise fewer than 30 manual steps. Do Android ROM developers not do CI builds? If this was all GPL I could make a strong case it's in breach. ("The source code for a work means the preferred form of the work for making modifications to it [...] all the source code for all modules it contains, plus any associated interface definition files, plus the scripts used to control compilation and installation of the executable."). Yes, I know, volunteers, spare time, teeth of gift horses, etc etc. End rant

Anyway, so far I am doing the following and it has not yet blown up

1) using the docker image from LineageOS for Microg

2) invoking it as follows

docker run \
    -e "BRANCH_NAME=lineage-15.1" \
    -e "DEVICE_LIST=potter" \
    -e "SIGN_BUILDS=false" \
    -e "SIGNATURE_SPOOFING=restricted" \
    -e "INCLUDE_PROPRIETARY=false" \
    -e "WITH_SU=true" \
    -e "CUSTOM_PACKAGES=GmsCore GsfProxy FakeStore MozillaNlpBackend NominatimNlpBackend com.google.android.maps.jar FDroid FDroidPrivilegedExtension " \
    -v "/$HOME/src/android/l4mg/lineage:/srv/src" \
    -v "/$HOME/src/android/l4mg/zips:/srv/zips" \
    -v "/$HOME/src/android/l4mg/logs:/srv/logs" \
    -v "/$HOME/src/android/l4mg/cache:/srv/ccache" \
    -v "/$HOME/src/android/l4mg/keys:/srv/keys" \
    -v "/$HOME/src/android/l4mg/manifests:/srv/local_manifests" \

3) with this manifest in $HOME/src/android/l4mg/manifests/roomservice.xml

<?xml version="1.0" encoding="UTF-8"?>
	<project name="LineageOS/android_external_bson" path="external/bson" remote="github" revision="cm-14.1" />
	<project name="LineageOS/android_device_qcom_common" path="device/qcom/common" remote="github" revision="lineage-15.1" />
	<project name="LineageOS/android_packages_resources_devicesettings" path="packages/resources/devicesettings" remote="github" revision="staging/lineage-15.1" />
	<project name="boulzordev/android_device_motorola_potter" path="device/motorola/potter" remote="github" revision="lineage-15.1-64" />
	<project name="boulzordev/android_vendor_motorola_potter" path="vendor/motorola/potter" remote="github" revision="lineage-15.1-64" />
	<project name="boulzordev/android_kernel_motorola_msm8953" path="kernel/motorola/msm8953" remote="github" revision="lineage-15.1-64" />

Worthy of note:

As I write this, it has been building for ~ 30 minutes and not fallen over yet, so things are looking vaguely promising

[  8% 8343/95970] target thumb C++: libv8src_32 <= external/v8/src/builtins/builtins-constructor.cc

Apparently it's done 8% of something

Update: Fri Feb 12 19:57:48 GMT 2021

It works! It built a buch of stuff in zips/potter/ including the file lineage-15.1-20210212-UNOFFICIAL-potter.zip which I installed from Recovery using the instructions at https://wiki.lineageos.org/devices/peregrine/install Yes, that's not the same phone, but it's close enough to use the same procedure