Debug Terminal: Echo Off function

[PropGit]

[EDITED with strikeouts where appropriate. See next post also]
We need to have an Echo Off feature (which is enabled by default; ie: echo is off by default).

This feature is needed because and electronic echo is always caused by the BASIC Stamp because of its circuitry. Anything transmitted to it is echoed back immediately to the sender (even if the BASIC Stamp is not powered).

The app has to purposely look for and remove echos in the Debug Terminal when the Echo Off feature is enabled. When this feature is enabled, any characters transmitted by Debug Terminal Transmit Pane activity should be counted matched (exactly, and in order, of course) and that same leading number of characters in the receive buffer and should be thrown away. In other words, the receive buffer parser must take the extra step to look for the same realize the count of the characters that were just transmitted (in order) and simply remove them from the stream before processing any further characters. One for one, in-order, match.

When the Echo Off feature is disabled, the special preprocessing of the receive buffer is not performed.

The related UI feature is noted in Issue #185.

[PropGit]

@2fast2fourier - I must have mis-remembered how this was implemented.

In my Debug.pas unit, the TransmitterKeyPress method simply increments a counter for every character typed into the Transmit Pane:

    {Send character out the serial port, increment char count and time-stamp it}
    SerialPort[ID].SendData(Key);
    if EchoOffBox.Checked then
      begin {Set flags to filter out echoes}
      inc(TxCharCount);
      LastTxTime := GetTickCount;
      end;

Then, the RemoveEchoedChars method is called from a separate EventThread that monitors the serial port:

  if (TxCharCount > 0) and (GetTickCount < LastTxTime+(ReceiveDelay*ReceiveMultiplier)) then
    begin {Remove echoed characters from receive buffer}
    CharCount := SerialPort[ID].FlushRX(TxCharCount,1);
    TxCharCount := TxCharCount - CharCount;
    ...
    end
  else    {No echoed characters}
    TxCharCount := 0;

And it appears that I made it only remove echoed characters that are received in less than 40 ms typically. The logic here is that the BASIC Stamp wouldn't respond with it's own characters (and the system wouldn't receive it) in that time, so characters received before that limit are likely to be electronic echos caused by the BASIC Stamp's serial circuitry; the very things we want to remove from the receive stream.

Here's how ReceiveDelay and ReceiveMultiplier are defined:

  ReceiveDelay      = 40; {Milliseconds to wait for data byte to be received on serial port (Used to calculate RxDelay)}
  ReceiveMultiplier = 6;  {Multiplier applied to ReceiveDelay to calculate RxDelay based on if the $PORT directive is
                           used or if only one serial port is available.  This for two purposes: 1) To support the
                           Stamper 900MHz devices (which have extra delays in tx/rx and 2) to support emulated Windows
                           within a different OS (which might have extra delays in tx/rx)}

[PropGit]

Verified enhanced.