Serial USB problem

Question

Hi all !

Newbie needs some help with serial port.

In my C# application I read data that are send from AVR chip to USB port.

I've defined my message structure like this (byte by byte in hex):

1. C3 -> start of message

2. xx -> address field

3. xx -> address field

4. xx -> data field

5. 3C -> end of message.

This is general structure of my messages, I mean the most important are START and END sequences to help me to process what is between them.

Messages are 30 bytes max. 

I use :

string indata;

indata = port.ReadExisting();

Problem is that from time to time I receive only half of my message and sometimes "empty string".

Received messages on PC are:

1. 3c 15 88 3 45 c3   OK

2. 3c 15 88 3 45 c3   OK

3. 3c 15 88 3 45 c3    OK

4. 88 3 45 c3 NOT OK

5. 3c 15 88 3 45 c3     OK

6. 3 NOT OK

7. 3c 15 88 3 45 c3     OK

8. 3 45 c3  NOT OK

9. (nothing) NOT OK

10.3c 15 88 3 45 c3     OK

.

.

.

How many bytes can USB port receive at ones? You know what I mean.

Maybe I overloaded this buffer?

Port parameters are OK, (baudrate,....)

Any idea?

Thank You and regards !