Add EXLA to enable use of at least CPU-based ML

Author: lawik

config/rpi4.exs

@@ -10,3 +10,5 @@ config :vintage_net,
   ]
 
 config :delux, indicators: %{default: %{green: "ACT"}}
+
+config :nx, default_backend: EXLA.Backend

config/rpi5.exs

@@ -14,3 +14,5 @@ config :delux, indicators: %{default: %{green: "ACT"}}
 # The RPi5 doesn't support WPA3 yet, but it also doesn't fail with the generic
 # configuration. This will enable WPA3 support when it's available.
 config :vintage_net_wifi, :quick_configure, &VintageNetWiFi.Cookbook.generic/2
+
+config :nx, default_backend: EXLA.Backend

mix.exs

@@ -11,12 +11,17 @@ defmodule NervesLivebook.MixProject do
 
   # See the BlueHeron repository for the boards that it supports.
   @ble_targets [:rpi0, :rpi3, :rpi3a]
+  @xla_targets [:rpi4, :rpi5]
 
   # Instruct the compiler to create deterministic builds to minimize
   # differences between firmware versions. This helps delta firmware update
   # compression.
   System.put_env("ERL_COMPILER_OPTIONS", "deterministic")
 
+  if Mix.target() in @xla_targets do
+    System.put_env("XLA_TARGET_PLATFORM", "aarch64-linux-gnu")
+  end
+
   def project do
     [
       app: @app,
@@ -110,6 +115,9 @@ defmodule NervesLivebook.MixProject do
       {:vega_lite, "~> 0.1"},
       {:vintage_net_wifi, "~> 0.12.5", targets: @all_targets},
       {:vintage_net_qmi, "~> 0.4.1", targets: @all_targets},
+      {:axon, "~> 0.7", targets: @xla_targets},
+      {:bumblebee, "~> 0.6", targets: @xla_targets},
+      {:exla, "~> 0.9", targets: @xla_targets},
 
       # Nerves system dependencies
       {:nerves_system_rpi, "~> 1.28", runtime: false, targets: :rpi},