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bk(4) [bsd man page]

BK(4)							     Kernel Interfaces Manual							     BK(4)

bk - line discipline for machine-machine communication (obsolete) SYNOPSIS
Not currently supported under 2.11BSD DESCRIPTION
This line discipline provides a replacement for the old and new tty drivers described in tty(4) when high speed output to and especially input from another machine is to be transmitted over a asynchronous communications line. The discipline was designed for use by the Berke- ley network. It may be suitable for uploading of data from microprocessors into the system. If you are going to send data over asynchro- nous communications lines at high speed into the system, you must use this discipline, as the system otherwise may detect high input data rates on terminal lines and disables the lines; in any case the processing of such data when normal terminal mechanisms are involved satu- rates the system. The line discipline is enabled by a sequence: #include <sgtty.h> int ldisc = NETLDISC, fildes; ... ioctl(fildes, TIOCSETD, &ldisc); A typical application program then reads a sequence of lines from the terminal port, checking header and sequencing information on each line and acknowledging receipt of each line to the sender, who then transmits another line of data. Typically several hundred bytes of data and a smaller amount of control information will be received on each handshake. The old standard teletype discipline can be restored by doing: ldisc = OTTYDISC; ioctl(fildes, TIOCSETD, &ldisc); While in networked mode, normal teletype output functions take place. Thus, if an 8 bit output data path is desired, it is necessary to prepare the output line by putting it into RAW mode using ioctl(2). This must be done before changing the discipline with TIOCSETD, as most ioctl(2) calls are disabled while in network line-discipline mode. When in network mode, input processing is very limited to reduce overhead. Currently the input path is only 7 bits wide, with newline the only recognized character, terminating an input record. Each input record must be read and acknowledged before the next input is read as the system refuses to accept any new data when there is a record in the buffer. The buffer is limited in length, but the system guarantees to always be willing to accept input resulting in 512 data characters and then the terminating newline. User level programs should provide sequencing and checksums on the information to guarantee accurate data transfer. SEE ALSO
None. BUGS
The Purdue uploading line discipline, which provides 8 bits and uses timeout's to terminate uploading should be incorporated into the stan- dard system, as it is much more suitable for microprocessor connections. 4th Berkeley Distribution January 27, 1996 BK(4)

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TTY(4)							   BSD Kernel Interfaces Manual 						    TTY(4)

tty -- general terminal interface SYNOPSIS
#include <sys/ioctl.h> DESCRIPTION
This section describes the interface to the terminal drivers in the system. Terminal Special Files Each hardware terminal port on the system usually has a terminal special device file associated with it in the directory ``/dev/'' (for exam- ple, ``/dev/tty03''). When a user logs into the system on one of these hardware terminal ports, the system has already opened the associated device and prepared the line for normal interactive use (see getty(8) .) There is also a special case of a terminal file that connects not to a hardware terminal port, but to another program on the other side. These special terminal devices are called ptys and provide the mechanism necessary to give users the same interface to the system when logging in over a network (using rlogin(1), or telnet(1) for example). Even in these cases the details of how the terminal file was opened and set up is already handled by special software in the system. Thus, users do not normally need to worry about the details of how these lines are opened or used. Also, these lines are often used for dialing out of a system (through an out-calling modem), but again the system provides programs that hide the details of accessing these terminal special files (see tip(1) ). When an interactive user logs in, the system prepares the line to behave in a certain way (called a line discipline), the particular details of which is described in stty(1) at the command level, and in termios(4) at the programming level. A user may be concerned with changing settings associated with his particular login terminal and should refer to the preceding man pages for the common cases. The remainder of this man page is concerned with describing details of using and controlling terminal devices at a low level, such as that possibly required by a program wishing to provide features similar to those provided by the system. Line disciplines A terminal file is used like any other file in the system in that it can be opened, read, and written to using standard system calls. For each existing terminal file, there is a software processing module called a line discipline is associated with it. The line discipline essentially glues the low level device driver code with the high level generic interface routines (such as read(2) and write(2) ), and is responsible for implementing the semantics associated with the device. When a terminal file is first opened by a program, the default line discipline called the termios line discipline is associated with the file. This is the primary line discipline that is used in most cases and provides the semantics that users normally associate with a terminal. When the termios line discipline is in effect, the terminal file behaves and is operated according to the rules described in termios(4). Please refer to that man page for a full description of the terminal semantics. The operations described here generally represent features common across all line disciplines, however some of these calls may not make sense in conjunction with a line discipline other than termios, and some may not be supported by the underlying hardware (or lack thereof, as in the case of ptys). Terminal File Operations All of the following operations are invoked using the ioctl(2) system call. Refer to that man page for a description of the request and argp parameters. In addition to the ioctl requests defined here, the specific line discipline in effect will define other requests specific to it (actually termios(4) defines them as function calls, not ioctl requests.) The following section lists the available ioctl requests. The name of the request, a description of its purpose, and the typed argp parameter (if any) are listed. For example, the first entry says TIOCSETD int *ldisc and would be called on the terminal associated with file descriptor zero by the following code fragment: int ldisc; ldisc = TTYDISC; ioctl(0, TIOCSETD, &ldisc); Terminal File Request Descriptions TIOCSETD int *ldisc Change to the new line discipline pointed to by ldisc. The available line disciplines are listed in ~ <sys/ttycom.h> and cur- rently are: TTYDISC Termios interactive line discipline. TABLDISC Tablet line discipline. SLIPDISC Serial IP line discipline. PPPDISC PPP line discipline. TIOCGETD int *ldisc Return the current line discipline in the integer pointed to by ldisc. TIOCSBRK void Set the terminal hardware into BREAK condition. TIOCCBRK void Clear the terminal hardware BREAK condition. TIOCSDTR void Assert data terminal ready (DTR). TIOCCDTR void Clear data terminal ready (DTR). TIOCGPGRP int *tpgrp Return the current process group the terminal is associated with in the integer pointed to by tpgrp. This is the underlying call that implements the termios(4) tcgetattr() call. TIOCSPGRP int *tpgrp Associate the terminal with the process group (as an integer) pointed to by tpgrp. This is the underlying call that implements the termios(4) tcsetattr() call. TIOCGETA struct termios *term Place the current value of the termios state associated with the device in the termios structure pointed to by term. This is the underlying call that implements the termios(4) tcgetattr() call. TIOCSETA struct termios *term Set the termios state associated with the device immediately. This is the underlying call that implements the termios(4) tcsetattr() call with the TCSANOW option. TIOCSETAW struct termios *term First wait for any output to complete, then set the termios state associated with the device. This is the underlying call that implements the termios(4) tcsetattr() call with the TCSADRAIN option. TIOCSETAF struct termios *term First wait for any output to complete, clear any pending input, then set the termios state associated with the device. This is the underlying call that implements the termios(4) tcsetattr() call with the TCSAFLUSH option. TIOCOUTQ int *num Place the current number of characters in the output queue in the integer pointed to by num. TIOCSTI char *cp Simulate typed input. Pretend as if the terminal received the character pointed to by cp. TIOCNOTTY void This call is obsolete but left for compatibility. In the past, when a process that didn't have a controlling terminal (see The Controlling Terminal in termios(4)) first opened a terminal device, it acquired that terminal as its controlling terminal. For some programs this was a hazard as they didn't want a controlling terminal in the first place, and this provided a mechanism to disassociate the controlling terminal from the calling process. It must be called by opening the file /dev/tty and calling TIOCNOTTY on that file descriptor. The current system does not allocate a controlling terminal to a process on an open() call: there is a specific ioctl called TIOSCTTY to make a terminal the controlling terminal. In addition, a program can fork() and call the setsid() system call which will place the process into its own session - which has the effect of disassociating it from the controlling terminal. This is the new and preferred method for programs to lose their controlling terminal. TIOCSTOP void Stop output on the terminal (like typing ^S at the keyboard). TIOCSTART void Start output on the terminal (like typing ^Q at the keyboard). TIOCSCTTY void Make the terminal the controlling terminal for the process (the process must not currently have a controlling terminal). TIOCDRAIN void Wait until all output is drained. TIOCEXCL void Set exclusive use on the terminal. No further opens are permitted except by root. Of course, this means that programs that are run by root (or setuid) will not obey the exclusive setting - which limits the usefulness of this feature. TIOCNXCL void Clear exclusive use of the terminal. Further opens are permitted. TIOCFLUSH int *what If the value of the int pointed to by what contains the FREAD bit as defined in ~ <sys/file.h>, then all characters in the input queue are cleared. If it contains the FWRITE bit, then all characters in the output queue are cleared. If the value of the integer is zero, then it behaves as if both the FREAD and FWRITE bits were set (i.e. clears both queues). TIOCGWINSZ struct winsize *ws Put the window size information associated with the terminal in the winsize structure pointed to by ws. The window size struc- ture contains the number of rows and columns (and pixels if appropriate) of the devices attached to the terminal. It is set by user software and is the means by which most full-screen oriented programs determine the screen size. The winsize structure is defined in ~ <sys/ioctl.h>. TIOCSWINSZ struct winsize *ws Set the window size associated with the terminal to be the value in the winsize structure pointed to by ws (see above). TIOCCONS int *on If on points to a non-zero integer, redirect kernel console output (kernel printf's) to this terminal. If on points to a zero integer, redirect kernel console output back to the normal console. This is usually used on workstations to redirect kernel mes- sages to a particular window. TIOCMSET int *state The integer pointed to by state contains bits that correspond to modem state. Following is a list of defined variables and the modem state they represent: TIOCM_LE Line Enable. TIOCM_DTR Data Terminal Ready. TIOCM_RTS Request To Send. TIOCM_ST Secondary Transmit. TIOCM_SR Secondary Receive. TIOCM_CTS Clear To Send. TIOCM_CAR Carrier Detect. TIOCM_CD Carrier Detect (synonym). TIOCM_RNG Ring Indication. TIOCM_RI Ring Indication (synonym). TIOCM_DSR Data Set Ready. This call sets the terminal modem state to that represented by state. Not all terminals may support this. TIOCMGET int *state Return the current state of the terminal modem lines as represented above in the integer pointed to by state. TIOCMBIS int *state The bits in the integer pointed to by state represent modem state as described above, however the state is OR-ed in with the cur- rent state. TIOCMBIC int *state The bits in the integer pointed to by state represent modem state as described above, however each bit which is on in state is cleared in the terminal. SEE ALSO
stty(1), ioctl(2), pty(4), termios(4), getty(8) 4th Berkeley Distribution August 14, 1992 4th Berkeley Distribution
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