Hi all,

I have a program which recvs a character from the serial port and based on that does some other operations. I have a sniffer which keeps looking at the serial port and something strange is happening. Although the device attached to the serial port sends the correct characters, my program stores it in a messed up state. Not sure whats happening. For Eg::

The device sends::
00 01 A0 5F

My app stores::
00 01 20 5F

I am storing the incoming characters in a que of 'unsigned chars' . Not sure where I am losing the bits. Any clue on what might have happened?

Another example is as below

The device sends:
08 01 FF F8

My app stores::
00 01 7F 78


Some kind of bit manipulation happening when I am storing them? Is unsigned char the proper way to store raw hex bytes coming out of the serial port. When I send the commands to the serail port things are going fine, because the response of "00 01 A0 5F" is got when I send "A0 5F 00 00 01" and this is going out properly. And these are sent by stpring them in unisgned char buffer and sending them.

What kind of storage type might have messed
A0 to 20
or
FF to 7F
or
F8 to 78

Take a look at the termios functions, the serial port can be configured to transmit 5,6,7,8 bits per byte.

randy:
thanks for the response. I had tried all those. If given any lesser than 8 bits, the complete stream is messy.

After meddling around for a bit I found out what the issue was.

For people who might face such issue, here is the solution. You can thank me when you face this problem.

there is an attribute to the serial port(infact any terminal) called "istrip". You need to disable this. istrip strips the higher bit in an incoming stream and hence I was loosing out bits.

you can use stty -istrip -F /dev/ttySx where x is your serial port number.


tata for now
KD

If that is the case, then why is the first byte 0x08, stored as 0x00? Was the first byte actually 0x80? Maybe you also lost a bit on transmission for that run.

elyk,

well that kinda puzzled me 4 a while too. but since the issue got resolved i just bundled my doubts and threw it in the pacific.
rest assured, if u r facing such an issue, "istrip" will resove it.

The termios functions can also turn on/off the istrip flag. This is how the stty function does it.