Read and write mailbox bytes separately.

lib/pca9641.ex

@@ -44,6 +44,7 @@ defmodule PCA9641 do
           :bus_hung | :mbox_full | :mbox_empty | :test_int | :lock_grant | :bus_lost | :int_in
 
   @type t :: %PCA9641{conn: Conn.t(), int_pin: Conn.t()}
+  @type mailbox_data :: <<_::16>>
   @type acquire_options :: [acquire_option]
   @type acquire_option :: {:conn, Conn.t(), int_pin: Conn.t()}
 
@@ -971,17 +972,21 @@ defmodule PCA9641 do
   @doc """
   Read shared mailbox.
   """
-  @spec read_mailbox(t) :: {:ok, binary, t} | {:error, term}
+  @spec read_mailbox(t) :: {:ok, mailbox_data, t} | {:error, term}
   def read_mailbox(%PCA9641{conn: conn} = dev) do
-    with {:ok, mailbox} <- Registers.read_mailbox(conn), do: {:ok, mailbox, %{dev | conn: conn}}
+    with {:ok, <<lsb>>} <- Registers.read_mailbox_lsb(conn),
+         {:ok, <<msb>>} <- Registers.read_mailbox_msb(conn),
+         do: {:ok, <<msb, lsb>>, %{dev | conn: conn}}
   end
 
   @doc """
   Write shared mailbox.
   """
-  @spec write_mailbox(pid, binary) :: :ok | {:error, term}
-  def write_mailbox(%PCA9641{conn: conn} = dev, data) when byte_size(data) == 2 do
-    with {:ok, conn} <- Registers.write_mailbox(conn, data), do: {:ok, %{dev | conn: conn}}
+  @spec write_mailbox(pid, mailbox_data) :: :ok | {:error, term}
+  def write_mailbox(%PCA9641{conn: conn} = dev, <<msb, lsb>>) do
+    with {:ok, conn} <- Registers.write_mailbox_lsb(conn, <<lsb>>),
+         {:ok, conn} <- Registers.write_mailbox_msb(conn, <<msb>>),
+         do: {:ok, %{dev | conn: conn}}
   end
 
   @doc """

lib/pca9641/registers.ex

@@ -12,5 +12,6 @@ defmodule PCA9641.Registers do
   defregister(:reserve_time, 0x03, :rw, 1)
   defregister(:interrupt_status, 0x04, :rw, 1)
   defregister(:interrupt_mask, 0x05, :rw, 1)
-  defregister(:mailbox, 0x06, :rw, 2)
+  defregister(:mailbox_lsb, 0x06, :rw, 1)
+  defregister(:mailbox_msb, 0x07, :rw, 1)
 end

test/pca9641_test.exs

@@ -892,8 +892,11 @@ defmodule PCA9641Test do
   describe "read_mailbox/1" do
     test "returns the contents of the MAILBOX register" do
       Registers
-      |> expect(:read_mailbox, 1, fn _conn ->
-        {:ok, <<0x1, 0x2>>}
+      |> expect(:read_mailbox_msb, 1, fn _conn ->
+        {:ok, <<0x1>>}
+      end)
+      |> expect(:read_mailbox_lsb, 1, fn _conn ->
+        {:ok, <<0x2>>}
       end)
 
       assert {:ok, <<0x1, 0x2>>, _conn} = PCA9641.read_mailbox(conn())
@@ -903,8 +906,12 @@ defmodule PCA9641Test do
   describe "write_mailbox/2" do
     test "writes the contents of the MAILBOX register" do
       Registers
-      |> expect(:write_mailbox, 1, fn conn, data ->
-        assert <<0x1, 0x2>> == data
+      |> expect(:write_mailbox_msb, 1, fn conn, data ->
+        assert <<0x1>> == data
+        {:ok, conn}
+      end)
+      |> expect(:write_mailbox_lsb, 1, fn conn, data ->
+        assert <<0x2>> == data
         {:ok, conn}
       end)