UNIX Terminals. Terminology. Serial Ports. Serial connection. Terminal Types. Terminal Types

Transcription

1 Terminology UNIX Terminals bps Bits per second, the rate at which data is transmitted baud The number of electrical state transitions that may be made in a period of time DTE Data Terminal Equipment your computer DCE Data communication Equipment modem RS-232 The common EIA standard for serial communication. There are also RS-423, RS-422, RS-485 Serial Ports Is an asynchronous port which transmit one bit of data at a time Are bi-directional Most of them obey some variant of the RS-232 standard Signal voltage is +/- 15V DC +/- 5V is the common value Serial ports relay on a special controller chip, the Universal Asynchronous Receiver Transmitter (UART) IT takes the parallel output of the computer and transform it into serial form of transmission. Speed usually is up to 115 Kbps Cable length is typically 50 feet maximum Serial connection Usually the serial connection are DB25 and DB9: Dumb Terminals Terminal Types Are specialized pieces of hardware that let you connect to computers over serial lines Called dumb because they have only enough computational power to display, send and receive text Digital Equipment Corporation s VT-100 (one of the most famous ones) Terminal Types Pcs acting as Terminals Any PC can act as a dumb terminal using a terminal emulation software. On FreeBSD tip(1) can be used On LINUX minicom(1) X11 Terminals Doesn t connect over serial line but use pseudo terminals Can display any X application 1

2 Terminal Modes - Cannonical Terminal input is processed as lines The terminal driver return one line per read request A line is delimited by a newline \n character end-of-file (EOF) character end-of-line (EOL) character Erase and kill processing occur when either of two special characters ERASE and KILL are received Terminal Mode - Noncanonical Input bytes are not assembled into lines Erase and kill processing does not occur The canonical mode is the default This can be seen when we use the read built in command of the shell Programs that manipulate the entire screen use non-canonical mode Input and Output queues There is an implied link between the input queue and the output queue when echo is enabled In most UNIX systems when the input queue is full the bell character is echoed Special Characters INTR Generate SIGINT signal which is sent to all processes in the foreground process group for which the terminal is the controlling terminal Quit Generate SIGQUIT ERASE In canonical mode erase the last character in the current line Special Characters (cont) KILL In canonical mode deletes the entire line EOF In canonical mode cause all the bytes waiting to be read to be passed immediately to the process without waiting to new line NL In canonical mode this is the line delimiter EOL An additional line delimiter Special Characters (cont) SUSP Generate SIGSTP signal to be sent to all the processes in the foreground STOP Special character on both input and output Can be used to temporary suspend output START The opposite of STOP CR \r from the C standard 2

3 Programming Interface All the terminal device characteristics that can be viewed/changed are in the termios structure (termios.h) struct termios { tcflag_t c_iflag; /* input flags */ tcflag_t c_oflag; /* output flags */ tcflag_t c_cflag; /* control flags */ tcflag_t c_lflag; /* local flags */ cc_t c_cc[nccs]; /* control chars */ speed_t c_ispeed; /* input speed */ speed_t c_ospeed; /* output speed */ ; Programming interface Input flags control the input of characters be the terminal device drive Output flags control the driver output (perform output processing, map new line to CR/LF..) Control flags effects the RS232 serial lines (ignore modem status line, one or two stop bits per character..) Local Flags effects the interface between the driver and the user (echo on or off, visually erase characters, enable terminal generated signals..) #define MAX_PASS_LEN 8 /* max #chars for user can enter */ Programming Interface tcgetattr fetch attributes (termios structure) tcsetattr set attributes (termios structure) cfgetispeed get input speed cfgetospeed get output speed cfsetispeed set input speed cfsetospeed set output speed tcdrain wait for all output to be transmitted tcflow suspend transmit or receive tcflush flush pending input and/or output tcsendbreak send BREAK character tcgetpgrp get foreground process group ID tcsetpgrp set foreground process group ID char *getpass(const char *prompt) { static char buf[max_pass_len + 1]; /* null byte at end */ char *ptr; sigset_t sig, sigsave; struct termios term, termsave; FILE *fp; int c; if ((fp = fopen(ctermid(null), "r+")) == NULL) return NULL; setbuf(fp, NULL); sigemptyset(&sig); sigaddset(&sig, SIGINT); sigaddset(&sig, SIGTSTP); sigprocmask(sig_block, &sig, &sigsave); tcgetattr(fileno(fp), &termsave); term = termsave; term.c_lflag &= ~(ECHO ECHOE ECHOK ECHONL); tcsetattr(fileno(fp), TCSAFLUSH, &term); fputs(prompt, fp); ptr = buf; while( (c = getc(fp))!= EOF && c!= '\n') { if(ptr < &buf[max_pass_len]) *ptr++ = c; *ptr = 0; putc('\n', fp); tcsetattr(fileno(fp), TCSAFLUSH, &termsave); sigprocmask(sig_setmask, &sigsave, NULL); fclose(fp); int main(int argc, char **argv) { char *pass_ptr; pass_ptr = getpass("enter Password:"); if(pass_ptr) printf("got password %s\n", pass_ptr); return 0; return (buf); Pseudo Terminals Pseudo Terminals A pseudo terminal is a pair of character devices master and slave The slave device provides to a process an interface identical to that of a terminal But this time there is no hardware device behind the device driver Instead another process is manipulating it through the master half of the pseudo terminal User Process Read/Write Functions Pseudo Terminal Master User Process Read/Write Functions Terminal Line Discipline Pseudo Terminal Slave 3

4 Pseudo Terminal script example Serial Console Many OS have the ability to boot the system with only a dumb terminal on a serial port as a console Useful for Installing machines which has not keyboards or screen attached Debugging kernels and device drivers Terminal servers can be used to manage/debug many pc s connected only to a serial line /etc/ttys Holds information that is used by various routines to initialize and control the use of terminal special files This information can be read using the getttyent(3) routine There is one line per special device file Field 1: Name of terminal special file Field 2: Command to execute for the line Field 3: Type of terminal connected, normally the name is found in /etc/termcap Field 4: Flags A flag value of on or off specify that init should (shouldn t) execute the command given in the second field A flag value of secure allows users with uid 0 to login on this line /etc/tty Example Root login on console at 1200 baud console "/usr/libexec/getty std.1200" vt100 on secure Virtual Terminal ttyv1 "/usr/libexec/getty Pc" cons25 on secure Serial Terminal ttyd0 "/usr/libexec/getty std.9600" dialup off secure Dialup at 1200 baud, no root logins ttyd0 "/usr/libexec/getty d1200" dialup on group=dialup # /etc/termcap Terminal capability data base The termcap file is a database file describing terminals Terminals are described by giving a set of capabilities that they have Describing how operations are performed Example: (the kermit terminal) kermit standard kermit:\ :bs:cd=\ej:ce=\ek:cl=\ee:cm=\ey%+ %+ :co#80:ho=\eh:li#24:nd=\ec:up=\ea:\ :ku=^k:kd=^j:kl=^h:kr=^l:kh=^^:ma=^hh\012j^kk^ll^^h:\ :is=k0 Standard Kermit \n: Termcap Example bs uses ^H to move left cd clear to end of screen ce clear to end of line cl clear screen and home cursure cm move to row #1 and culumns #2 co number of columns in a line ho home cursor li number of lines on screen or page nd move right one space 4

5 tty returns user terminal name On an xterm: ttyp9>>tty /dev/ttyp9 On a virtual terminal: ttyv1 On a serial line: ttyd0 stty set an option for a terminal stty set or reports on terminal characteristics for the device that is its standard input stty 9600 even tabs stty intr ^C kill ^U erase ^H -tabs When stdin is a file: ttyp9>>tty < typescript not a tty stty a ttypa>>stty -a speed 9600 baud; 24 rows; 80 columns; lflags: icanon isig iexten echo echoe -echok echoke -echonl echoctl -echoprt -altwerase -noflsh -tostop -flusho pendin -nokerninfo -extproc iflags: -istrip icrnl -inlcr -igncr ixon -ixoff ixany imaxbel -ignbrk brkint -inpck -ignpar -parmrk oflags: opost onlcr -ocrnl -oxtabs -onocr -onlret cflags: cread cs8 -parenb -parodd hupcl -clocal -cstopb -crtscts -dsrflow -dtrflow -mdmbuf cchars: discard = ^O; dsusp = ^Y; eof = ^D; eol = <undef>; eol2 = <undef>; erase = ^?; erase2 = ^H; intr = ^C; kill = ^U; lnext = ^V; min = 1; quit = ^\; reprint = ^R; start = ^Q; status = ^T; stop = ^S; susp = ^Z; time = 0; werase = ^W; tset, reset terminal initialization First tset determine the type of the terminal you are using When invoked as reset tset sets/unset the follwing: turn on coked and echo mode turn off cbreak and raw mode turn on newline translation mode set all special characters to their default values Options: -e ch -i ch -k ch -S set the erase character to ch set the interrupt character to ch set the kill character to ch print the terminal type and termcap entry to stdout tset -S ttyp9>>tset -S Erase is backspace. xterm xterm vs100:li#65:kh=\eoh:@7=\eof:kb=^h:kd=^?:k1=\eop:k2=\eoq:k3=\eor:k4= \EOS:km:is=\E>\E[?1;3;4;5l\E[?7;8h\E[1;65r\E[65;1H:rs=\E>\E[?1;3;4;5l\E[?7;8h:k I=\E[2~:kN=\E[6~:kP=\E[5~:k6=\E[17~:k7=\E[18~:k8=\E[19~:k9=\E[20~:k;=\E[21~:k5= \E[15~:ve=\E[?25h:vi=\E[?25l:k0@:im@:ei@:F1=\E[23~:F2=\E[24~:ic=\E[@:IC=\E[%d@: ec=\e[%dx:al=\e[l:dl=\e[m:mi:dc=\e[p:al=\e[%dl:dl=\e[%dm:dc=\e[%dp:do=\e[b:cl=\ E[H\E[J:sf=\ED:as=\E(0:ae=\E(B:cm=\E[%i%d;%dH:nd=\E[C:up=\E[A:nw=\EE:ce=\E[K:cd =\E[J:so=\E[7m:se=\E[m:us=\E[4m:ue=\E[m:md=\E[1m:mr=\E[7m:mb=\E[5m:me=\E[m:sr=\ EM:sc=\E7:rc=\E8:cs=\E[%i%d;%dr:UP=\E[%dA:DO=\E[%dB:RI=\E[%dC:LE=\E[%dD:ct=\E[3 g:st=\eh:co#80:le=^h:bs:am:if=/usr/share/tabset/vt100:ho=\e[h:ac=llmmkkjjuuttvv wwqqxxnnpprr\140\140aa:ks=\e[?1h\e=:ke=\e[?1l\e>:ku=\eoa:kd=\eob:kr=\eoc:kl=\eo D:@8=\EOM:K1=\EOq:K2=\EOr:K3=\EOs:K4=\EOp:K5=\EOn:pt:vt#3:xn:ta=^I:ms:bl=^G:cr= ^M:eo:it#8:ut:RA=\E[?7l:SA=\E[?7h:ttyp9>> 5