On Dec 19, 2007 3:41 PM, A.Krishnan <ridgetwo@xxxxxxxxxxxxx> wrote:
> 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
Damn, I haven't worked on serial ports in 10+ years. Brings back memories.
Historically the issue with serial ports is the handshaking. You
don't say what your doing, but you almost always need the UART to be
managing the handshaking without the kernel being involved. If you
are expecting the kernel to always respond to every interrupt before
the data overflows the UARTs buffer, your going to be unhappy
eventually. (unless your writing a realtime app, etc.)
And of course you need the 2 UARTs set to the same handshaking mode
(Xon/Xoff or hardware).
If you go with hardware, then you have to ensure you have the correct
pins connected on the serial connector. To verify that I always used
a serial breakout box with little lights. Used to be available for
$10 or $20 each for cheap ones. $100 or so for a good one.
Personally, I used to start with Xon/Xoff (cntrl-s/cntrl-q) because
it was the easiest to get working. Then, I would move to using
hardware handshaking because it was more reliable. (RTS/CTS etc.
iirc)
Greg
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