/// <summary>
/// Read from serial provider with retry
/// </summary>
/// <returns>Data from port or null on error</returns>
private byte[] TryPortRead()
{
var backoff = TimeSpan.Zero;
var retry = 3;
byte[] deviceData;
do
{
// Device always responds with 11 bytes
deviceData = SerialProvider.Read(11);
if (backoff != TimeSpan.Zero)
{
Thread.Sleep(backoff);
}
backoff += TimeSpan.FromMilliseconds(50);
} while (deviceData is null && retry-- > 0);
return(deviceData);
}
/// <summary>
/// Send poll message to device and return a validated response.
/// If the response is malformed, null will be returned.
/// </summary>
/// <returns>Device response</returns>
private ApexResponseMessage SendPollMessage()
{
// Replay the last message or build a new message
var nextMessage = _apexState.LastMessage ?? GetNextHostMessage();
var payload = nextMessage.Serialize();
SerialProvider.Write(payload);
// Device always responds with 11 bytes
var deviceData = TryPortRead();
var pollResponse = new ApexResponseMessage(deviceData);
// Log the parsed command and response together for easier analysis
Logger?.Trace("{0} poll message: {1}", GetType().Name, nextMessage);
Logger?.Trace("{0} poll response: {1}", GetType().Name, pollResponse);
// The response was invalid or incomplete
if (!pollResponse.IsValid)
{
// Request retransmission (by not modifying the ACK and payload)
_apexState.LastMessage = nextMessage;
// Update counter for responsive check
if (pollResponse.IsEmptyResponse)
{
_apexState.NonResponsiveCount++;
}
// If there is a protocol violation and strict mode is enabled,
// report the problem and request a retransmit
if (pollResponse.HasProtocolViolation && Config.StrictMode)
{
Logger?.Error("{0} Invalid message: {1}", GetType().Name, deviceData.ToHexString());
Logger?.Error("{0} Problems: {1}", GetType().Name,
string.Join(Environment.NewLine, pollResponse.AllPacketIssues));
return(null);
}
// Target is responsive, this is just a bad message
if (!IsUnresponsive)
{
return(null);
}
// Target is unresponsive, check if client needs to be notified
if (!_apexState.NotifiedLostConnection)
{
LostConnection();
_apexState.NotifiedLostConnection = true;
}
Logger?.Trace("{0} Device is not responding", GetType().Name);
return(null);
}
// If ACK does not match, then device is requesting a retransmit
if (nextMessage.Ack != pollResponse.Ack)
{
// Request retransmission
_apexState.LastMessage = nextMessage;
return(null);
}
// Update state with successful polling notification
_apexState.RegisterSuccessfulPoll();
return(pollResponse);
}
