UART - Raspberry Pi Hardware Reference - page 102

Use the tcgetattr(3) function to fetch the current serial device settings:

int tcgetattr(int fd, struct termios *termios_p);

where
fd is the open TTY file descriptor.
termios_p is the struct to be filled with current setting information.

struct termios term;
int rc;

rc = tcgetattr(fd,&term);
if ( rc < 0 ) {
perror("tcgetattr(3)");

tcsetattr(3)
When the termios structure has been defined with the serial parameters you wish to use,
the tcsetattr(3) call is used to set them in the device driver:

int tcsetattr(
int fd,
int optional_actions,
const struct termios *termios_p
);

where
fd is the open TTY file descriptor to change.
optional_actions is one of three actions (listed in the following table).
termios_p is a pointer to the new settings to be applied.
The three choices for optional_actions are as follows:

optional_actions Meaning

TCSANOW The change occurs immediately.

TCSADRAIN Change occurs after all output has been sent.

TCSAFLUSH As TCSADRAIN, but pending input is discarded.