UM0851 datasheet(101/245 Pages) STMICROELECTRONICS

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UM0851

Communication device drivers

Doc ID 16604 Rev 2

101/245

"/dev/ttyS0" or

"/dev/ttyS1" in case of SPEAr 600

The flags argument is an int that specifies how the file is to be opened;

the main values are

O_RDONLY open for reading only

O_WRONLY open for writing only

O_RDWR open for both reading and writing

The perms argument is always zero for the uses of open. */

fd = open(name, flags, perms);

Configure

The serial interface is used for changing parameters such as baud rate, character size, and

so on. The first thing you need to do is to include the file <termios.h>.

Here we use the ioclt() system calls. It takes three arguments:

IOCTL() system call

/* The fd argument specifies the serial port file descriptor

The request argument is a constant defined in the <termios.h> header file and

is typically one of the constants listed in Table 4.

The 3rd argument depends upon the particular control request, but it shall be

either an integer or a pointer to a device-specific data structure. */

int ioctl(int fd, int request, ... /*arg*/ );

Setting the baud rate

The cfsetospeed() and cfsetispeed() functions are provided to set the baud rate in the

termios structure regardless of the underlying operating system interface. These are user

level functions which do not implement any system calls.

/* TCGETS and struct termios fill all the current termios parameters like

baudrate etc.*/

ioctl (fd, TCGETS, &termios);

Table 32.

IOCTL requests for serial ports

Request

Description

TCGETS

Gets the current serial port settings.

TCSETS

Sets the serial port settings immediately.

TCSETSF

Sets the serial port settings after flushing the input and output

buffers.

TCSETSW

Sets the serial port settings after allowing the input and output

buffers to drain/empty.

TCSBRK

Sends a break for the given time.

TCXONC

Controls software flow control.

TCFLSH

Flushes the input and/or output queue.

TIOCMGET

Returns the state of the "MODEM" bits.

TIOCMSET

Sets the state of the "MODEM" bits.

FIONREAD

Returns the number of bytes in the input buffer.

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