managing termios for ser ports
 

I am trying to follow an example for simple serial port IO. ttyS0 for example.

I have a problem with the termios values particularly c_cflag and or cfsetispeed / cfsetospeed.

For the funtion cfsetispeed for example, it refers to a value like B38400, which they say is defined as 38400, or, #define B38400 38400. But using the other method to set termios.c_cflag it's supposed to be an OR of varios controls, like ( CS8 | B38400 | CLOCAL | CREAD ) for instance. Here obvious B38400 = 38400 is obviously not compatible to this flag setting. The bits would conflict with others.

In my termbits.h it says the following
#define B38400 00000017 !!!!
NOTE it does NOT say
#define B38400 0x00000017

If I use cfsetispeed (with B38400) c_cflag is not changed ( using 38400 or 0x00000017 or B_38400 ).

I cannot make the serial port work, even though the "open" returns a good fd.

What is going on??

DavidHB

B38400 not defined as 38400. It's 'something' that reflects the baudrate 38400. The value is 15 which matches your termbits.h (00000017 is an octal value, so 1*8 + 7 = 15). You can print the value with a simple printf.

I've posted an init routine that I usually use in this thread

Wim,

Thanks for the clarification. It hadn't occured to me that it was octal, and some other references that I had seen indicated that B38400 defined directly to 38400(??) so I was left with a confusion. Hex ( or Octal ) made more sense to me. I'm not at my office today, but when I get back I'll take another look.

Thanks for the in depth response.

Dave