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Delphi D4: using pointers to transfer data from COMM queue to circular queue

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I have an application that uses a serial port component to read and write 
data through a USB serial port at 57.6 kb. Originally I used the SerialNG 
component and with some tweaking I was able to get it to work reliably. But 
it has problems with Win10, so I changed the code to use ComDrv32, which 
works when used in a simple TTY demo.

The SerialNG component uses clusters or packets which can be set to a range 
of values. I am communicating with a USB device set up as a CDC serial 
emulator using Microchip PIC18F2550. It is basically a data acquisition unit 
that samples at 2400 samples/sec with a 10 bit ADC. I am splitting the data 
into two 5 bit values in 8 bit data characters, and I'm using the remaining 
three to identify the data as a MSB or LSB  (using one evem/odd bit), and a 
two bit value to determine if the data has been received in proper sequence.

Here is the function that receives the data from the serial port component:

===============================================================
procedure TfmCommLib.CommPortDriver1ReceiveData(Sender: TObject;
  DataPtr: Pointer; DataSize: Cardinal);
var
          RecdPtr: PChar;
          CSize, NCSize : Integer;
          n: Integer;
begin
  RecdPtr := PChar(DataPtr);
  RxDcount := DataSize;
  if RxDcount > MaxRxDcount then
    MaxRxDcount := RxDcount;
  if CommBufferPtr + DataSize >= MAXCOMM then begin
     move( DataPtr^, CommBuffer[CommBufferPtr], MAXCOMM-CommBufferPtr );
     n := DataSize - (MAXCOMM-CommBufferPtr);
     RecdPtr := RecdPtr+n;
     DataPtr := RecdPtr;
     CommBufferPtr := 0;
     move( DataPtr^, CommBuffer[CommBufferPtr], n );
     end
  else begin
       move( DataPtr^, CommBuffer[CommBufferPtr], DataSize );
       CommBufferPtr := CommBufferPtr + DataSize; end;
  CommCharCount := CommCharCount + DataSize;
  if(CommCharCount > MAXCOMM) then
       CommCharCount := MAXCOMM+1;
  end;
========================================================

It works, but I get errors after running for about 20 seconds. That 
corresponds to the point where the CommBuffer will overflow the MAXCOMM 
value of 100,000 (4800*20). My previous code for SerialNG used a cluster 
size of 2 and a loop to transfer the received data to the buffer one byte at 
a time. When I tried that, it seemed to work poorly. So I used a variation 
of the method from the ComDrv32 TTY demo using move( DataPtr^, 
CommBuffer[CommBufferPtr], DataSize ); But you can see that I had to split 
the transfer when near the end of the queue.

I had to use a separate PChar pointer RecdPtr, and I also had to use an 
integer for the pointer arithmetic. Apparently Delphi does not allow RecdPtr 
:= RecdPtr + (DataSize - (MAXCOMM-CommBufferPtr) ); RecdPtr + n is OK. I'm 
not sure if I could just advance the DataPtr in the same way, since it is 
declared as a generic Pointer type.

I can't very well use the Delphi debugger to see what's happening, as the 
data is received continuously and there is no handshaking.

TIA for any suggestions.

Paul 

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Delphi D4: using pointers to transfer data from COMM queue to circular queue "P E Schoen" <paul@pstech-inc.com> - 2016-08-19 02:19 -0400
  Re: Delphi D4: using pointers to transfer data from COMM queue to circular queue "P E Schoen" <paul@pstech-inc.com> - 2016-08-19 03:58 -0400
    Re: Delphi D4: using pointers to transfer data from COMM queue to circular queue "P E Schoen" <paul@pstech-inc.com> - 2016-08-19 04:42 -0400
      Re: Delphi D4: using pointers to transfer data from COMM queue to circular queue Hans-Peter Diettrich <DrDiettrich1@aol.com> - 2016-08-19 12:34 +0200
    Re: Delphi D4: using pointers to transfer data from COMM queue to circular queue Hans-Peter Diettrich <DrDiettrich1@aol.com> - 2016-08-19 12:30 +0200
      Re: Delphi D4: using pointers to transfer data from COMM queue to circular queue "P E Schoen" <paul@pstech-inc.com> - 2016-08-19 20:54 -0400
        Re: Delphi D4: using pointers to transfer data from COMM queue to circular queue Hans-Peter Diettrich <DrDiettrich1@aol.com> - 2016-08-20 12:43 +0200
          Re: Delphi D4: using pointers to transfer data from COMM queue to circular queue "P E Schoen" <paul@pstech-inc.com> - 2016-08-20 19:15 -0400
            Re: Delphi D4: using pointers to transfer data from COMM queue to circular queue Hans-Peter Diettrich <DrDiettrich1@aol.com> - 2016-08-21 12:50 +0200
              Re: Delphi D4: using pointers to transfer data from COMM queue to circular queue "P E Schoen" <paul@pstech-inc.com> - 2016-08-22 07:12 -0400
  Re: Delphi D4: using pointers to transfer data from COMM queue to circular queue Hans-Peter Diettrich <DrDiettrich1@aol.com> - 2016-08-19 12:27 +0200

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