Make pure library and support >1 sensor

This moves the C algorithm code management out of a singleton GenServer
since it maintains per-sensor state. This also makes this package a pure
library and simplifies state handling in the port.

Author: fhunleth

lib/sgp40.ex

@@ -29,7 +29,14 @@ defmodule SGP40 do
 
   defmodule State do
     @moduledoc false
-    defstruct [:humidity_rh, :last_measurement, :serial_id, :temperature_c, :transport]
+    defstruct [
+      :humidity_rh,
+      :last_measurement,
+      :serial_id,
+      :temperature_c,
+      :transport,
+      :voc_index
+    ]
   end
 
   @default_bus_name "i2c-1"
@@ -58,6 +65,24 @@ defmodule SGP40 do
     GenServer.call(server, :measure)
   end
 
+  @spec get_states(GenServer.server()) ::
+          {:ok, SGP40.VocIndex.AlgorithmStates.t()} | {:error, any}
+  def get_states(server) do
+    GenServer.call(server, :get_states)
+  end
+
+  @spec set_states(GenServer.server(), SGP40.VocIndex.AlgorithmStates.t()) ::
+          {:ok, binary} | {:error, any}
+  def set_states(server, args) do
+    GenServer.call(server, {:set_states, args})
+  end
+
+  @spec set_tuning_params(GenServer.server(), SGP40.VocIndex.AlgorithmTuningParams.t()) ::
+          {:ok, binary} | {:error, any}
+  def set_tuning_params(server, args) do
+    GenServer.call(server, {:set_tuning_params, args})
+  end
+
   @doc """
   Update relative ambient humidity (RH %) and ambient temperature (degree C)
   for the humidity compensation.
@@ -82,13 +107,15 @@ defmodule SGP40 do
     case @transport_mod.open(bus_name: bus_name, bus_address: bus_address) do
       {:ok, transport} ->
         {:ok, serial_id} = SGP40.Comm.serial_id(transport)
+        {:ok, voc_index} = SGP40.VocIndex.start_link()
 
         state = %State{
           humidity_rh: humidity_rh,
           last_measurement: nil,
           serial_id: serial_id,
           temperature_c: temperature_c,
-          transport: transport
+          transport: transport,
+          voc_index: voc_index
         }
 
         {:ok, state, {:continue, :init_sensor}}
@@ -123,7 +150,7 @@ defmodule SGP40 do
              state.humidity_rh,
              state.temperature_c
            ),
-         {:ok, voc_index} <- SGP40.VocIndex.process(sraw) do
+         {:ok, voc_index} <- SGP40.VocIndex.process(state.voc_index, sraw) do
       timestamp_ms = System.monotonic_time(:millisecond)
       measurement = %SGP40.Measurement{timestamp_ms: timestamp_ms, voc_index: voc_index}
 
@@ -140,14 +167,22 @@ defmodule SGP40 do
     {:reply, {:ok, state.last_measurement}, state}
   end
 
+  def handle_call(:get_states, _from, state) do
+    {:reply, SGP40.VocIndex.get_states(state.voc_index), state}
+  end
+
+  def handle_call({:set_states, args}, _from, state) do
+    {:reply, SGP40.VocIndex.set_states(state.voc_index, args), state}
+  end
+
+  def handle_call({:set_tuning_params, args}, _from, state) do
+    {:reply, SGP40.VocIndex.set_tuning_params(state.voc_index, args), state}
+  end
+
   @impl GenServer
   def handle_cast({:update_rht, humidity_rh, temperature_c}, state) do
     state = %{state | humidity_rh: humidity_rh, temperature_c: temperature_c}
 
     {:noreply, state}
   end
-
-  defdelegate get_states, to: SGP40.VocIndex
-  defdelegate set_states(args), to: SGP40.VocIndex
-  defdelegate set_tuning_params(args), to: SGP40.VocIndex
 end

lib/sgp40/application.ex

@@ -2,34 +2,27 @@ defmodule SGP40.VocIndex do
   @moduledoc """
   Process the raw output of the SGP40 sensor into the VOC Index.
   """
+  use GenServer
 
   alias SGP40.VocIndex.AlgorithmStates
   alias SGP40.VocIndex.AlgorithmTuningParams
 
-  use GenServer, restart: :permanent
-
   require Logger
 
   @doc """
-  Initialize the VOC algorithm parameters. Call this once at the beginning or
-  whenever the sensor stopped measurements.
+  Initialize the VOC algorithm
   """
   @spec start_link(keyword()) :: GenServer.on_start()
-  def start_link(_args \\ []) do
-    case GenServer.start_link(__MODULE__, nil, name: __MODULE__) do
-      {:ok, pid} -> {:ok, pid}
-      # Stop this process and let the supervisor restart so that we can
-      # re-initialize the VOC algorithm.
-      {:error, {:already_started, pid}} -> GenServer.stop(pid, :normal)
-    end
+  def start_link(args \\ []) do
+    GenServer.start_link(__MODULE__, args)
   end
 
   @doc """
   Calculate the VOC index value from the raw sensor value.
   """
-  @spec process(0..0xFFFF) :: {:ok, 1..500} | {:error, any}
-  def process(sraw) do
-    GenServer.call(__MODULE__, {:process, sraw})
+  @spec process(GenServer.server(), 0..0xFFFF) :: {:ok, 1..500} | {:error, any}
+  def process(server, sraw) do
+    GenServer.call(server, {:process, sraw})
   end
 
   @doc """
@@ -38,30 +31,31 @@ defmodule SGP40.VocIndex do
   skipping initial learning phase. This feature can only be used after at least
   3 hours of continuous operation.
   """
-  @spec get_states :: {:ok, AlgorithmStates.t()} | {:error, any}
-  def get_states() do
-    GenServer.call(__MODULE__, :get_states)
+  @spec get_states(GenServer.server()) :: {:ok, AlgorithmStates.t()} | {:error, any}
+  def get_states(server) do
+    GenServer.call(server, :get_states)
   end
 
   @doc """
   Set previously retrieved algorithm states to resume operation after a short
   interruption, skipping initial learning phase. This feature should not be
-  used after inerruptions of more than 10 minutes. Call this once after
+  used after interruptions of more than 10 minutes. Call this once after
   `start_link/1` and the optional `set_tuning_params/1`, if
   desired. Otherwise, the algorithm will start with initial learning phase.
   """
-  @spec set_states(AlgorithmStates.t()) :: {:ok, binary} | {:error, any}
-  def set_states(args) do
-    GenServer.call(__MODULE__, {:set_states, args})
+  @spec set_states(GenServer.server(), AlgorithmStates.t()) :: {:ok, binary} | {:error, any}
+  def set_states(server, args) do
+    GenServer.call(server, {:set_states, args})
   end
 
   @doc """
   Set parameters to customize the VOC algorithm. Call this once after
   `start_link/1`, if desired. Otherwise, the default values will be used.
   """
-  @spec set_tuning_params(AlgorithmTuningParams.t()) :: {:ok, binary} | {:error, any}
-  def set_tuning_params(args) do
-    GenServer.call(__MODULE__, {:set_tuning_params, args})
+  @spec set_tuning_params(GenServer.server(), AlgorithmTuningParams.t()) ::
+          {:ok, binary} | {:error, any}
+  def set_tuning_params(server, args) do
+    GenServer.call(server, {:set_tuning_params, args})
   end
 
   @impl GenServer

lib/sgp40/voc_index.ex

@@ -27,8 +27,7 @@ defmodule SGP40.MixProject do
   # Run "mix help compile.app" to learn about applications.
   def application do
     [
-      extra_applications: [:logger],
-      mod: {SGP40.Application, []}
+      extra_applications: [:logger]
     ]
   end
 

mix.exs

@@ -3,34 +3,42 @@ defmodule SGP40.VocIndexTestTest do
   alias SGP40.VocIndex
 
   test "process" do
-    {:ok, voc_index} = VocIndex.process(123)
+    pid = start_supervised!(SGP40.VocIndex)
+
+    {:ok, voc_index} = VocIndex.process(pid, 123)
 
     assert is_integer(voc_index)
   end
 
   test "get_states" do
-    {:ok, states} = VocIndex.get_states()
+    pid = start_supervised!(SGP40.VocIndex)
+
+    {:ok, states} = VocIndex.get_states(pid)
 
     assert %{mean: mean, std: std} = states
     assert is_integer(mean)
     assert is_integer(std)
   end
 
   test "set_states" do
-    assert {:ok, echo} = VocIndex.set_states(%{mean: 1, std: 2})
+    pid = start_supervised!(SGP40.VocIndex)
+
+    assert {:ok, echo} = VocIndex.set_states(pid, %{mean: 1, std: 2})
 
     assert echo =~ ~r/mean:\d*,std:\d*/
   end
 
   test "set_tuning_params" do
+    pid = start_supervised!(SGP40.VocIndex)
+
     params = %{
       voc_index_offset: 1,
       learning_time_hours: 2,
       gating_max_duration_minutes: 3,
       std_initial: 4
     }
 
-    assert {:ok, echo} = VocIndex.set_tuning_params(params)
+    assert {:ok, echo} = VocIndex.set_tuning_params(pid, params)
 
     assert echo ==
              "voc_index_offset:1,learning_time_hours:2,gating_max_duration_minutes:3,std_initial:4"