serial port problem - help needed to debug

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Hello,

  I am using two computers. The serial i/o chip is 16550A based. It is
an old hardware and could not find more details. The two serial ports
(ttyS0) are connected by a null-modem cable. I am sending a simple
string (This is the tester) from one end to another end. I am running
2.6.9 kernel. With 9600 baudrate the receiving end I get either
  This is the test
or
  This is the test
  er

  If I use a baudrate of 19200 or 38400, I get the following string:
   T<00>his is
I interpreted this as a data corruption.  So I used 9600 baudrate at
both ends. I put a printk debug statement in 8250.c program ( procedure:
static void receive_chars(struct uart_8250_port *up, unsigned int
*status) )  The printk is after the following line:
                   do {
                ch = serial_inp(up, UART_RX);

Analysis of the received character did not reveal any missing of
characters.  I don't exactly know the flow of the serial driver
functions and hence not exactly knowing the next step in debugging.  So
I would like to get some guidance/direction/suggestions from others.
Also, I would like to have references for a HowTo/architecture of Linux
serial driver. Please let me know your input. Any help is appreciated to
solve this problem.

A. Krishnan



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