UART - Raspberry Pi Hardware Reference - page 109

cfsetispeed(3)
The cfsetispeed(3) function permits a portable way to establish an input baud rate in
the termios structure:
int cfsetispeed(struct termios * termios_p, speed_t speed);
where
termios_p is the pointer to the TTY configuration structure to be modified.
speed is the input baud rate to apply.
Note that this function only updates the termios data structure and has no direct
effect on the device being used.
struct termios term;
int rc;
rc = cfsetispeed(&term,115200);
if ( rc < 0 ) {
perror("cfsetispeed(3)");
cfsetospeed(3)
The cfsetospeed(3) function sets the output baud rate in the termios structure:
int cfsetospeed(struct termios * termios_p, speed_t speed);
where
termios_p is the pointer to the TTY configuration structure being modified.
speed is the output baud rate to apply.
Note that this function only updates the termios data structure with no direct effect
on the device being used.
struct termios term;
int rc;
rc = cfsetospeed(&term,9600);
if ( rc < 0 ) {
perror("cfsetospeed(3)");