Retry waking up ATECC on unexpected response

The original code had intentions of retrying the wake up processor, but
it never used it. I.e., the default number of retries was 1. This
changes the default to 4 and adds a 500 ms wait in between tries.

The logic for this is that wakeup errors can happen for many reasons
especially since it's possible for other programs to access to ATECC
simultaneously. This is definitely a problem with OpenSSL engines since
they're independent of this library. The strategy for this library is to
minimize calls to the ATECC via caching of responses to read-only data,
but it still happens and retries are needed.

4 retries separated by 500 ms was picked since 1. it's still well under
the 5 second default Erlang timer on calls, so function calls shouldn't
time out, and 2. 500 ms is longer than most ATECC ops, so there's a good
change that whatever conflicted is done.

lib/atecc508a/transport/i2c_server.ex

@@ -10,6 +10,8 @@ defmodule ATECC508A.Transport.I2CServer do
   @atecc508a_wake_delay_ms 2
   @atecc508a_signature <<0x04, 0x11, 0x33, 0x43>>
   @atecc508a_poll_interval_ms 2
+  @atecc508a_retry_wakeup_ms 500
+  @atecc508a_default_wakeup_retries 4
 
   @spec start_link(keyword()) :: :ignore | {:error, any()} | {:ok, pid()}
   def start_link([bus_name, address, process_name]) do
@@ -164,7 +166,7 @@ defmodule ATECC508A.Transport.I2CServer do
     end
   end
 
-  defp wakeup(i2c, address, retries \\ 1)
+  defp wakeup(i2c, address, retries \\ @atecc508a_default_wakeup_retries)
 
   defp wakeup(_i2c, _address, 0) do
     {:error, :unexpected_wakeup_response}
@@ -188,10 +190,12 @@ defmodule ATECC508A.Transport.I2CServer do
         :ok
 
       {:ok, something_else} ->
-        _ = sleep(i2c, address)
-
-        Logger.warn("Unexpected wakeup response: #{inspect(something_else)}. Retrying.")
+        Logger.warn(
+          "Unexpected wakeup response: #{inspect(something_else)}. #{retries - 1} retries remaining."
+        )
 
+        Process.sleep(@atecc508a_retry_wakeup_ms)
+        _ = sleep(i2c, address)
         wakeup(i2c, address, retries - 1)
 
       error ->