Ubuntu Manpage: tack - terminfo action checker

NAME

       tack - terminfo action checker

SYNOPSIS

       tack [-itV] [term]

DESCRIPTION

       The tack program has three purposes: (1) to help you build a new terminfo entry describing
       an unknown terminal, (2) to test the correctness of an existing entry, and (3) to  develop
       the  correct  pad  timings  needed  to  ensure  that screen updates do not fall behind the
       incoming data stream.

       Tack presents a series of screen-painting and interactive tests in ways which are intended
       to make any mismatches between the terminfo entry and reality visually obvious.  Tack also
       provides tools that can help in understanding how the terminal operates.

   OPTIONS
       -i     Usually tack will send the reset and init strings to the terminal when the  program
              starts up.  The -i option will inhibit the terminal initialization.

       -t     Tell  tack  to  override  the terminfo settings for basic terminal functions.  When
              this option is set tack will translate (cr) to \r, (cud1) to \n, (ind) to \n, (nel)
              to \r\n, (cub1) to \b, (bel) to \007, (ff) to \f and (ht) to \t.

       -V     Display the version information and exit.

       term   Terminfo  terminal  name  to  be tested.  If not present then the $TERM environment
              variable will be used.

OVERVIEW

Since tack is designed to test terminfo entries it is not possible to rely on the
correctness of the terminfo data base. Because of this the menuing system used with tack
is vary primitive. When a menu is printed it will scroll the entire screen. To
compensate for this verbose menu system tack permits menu selection type ahead. If you
already know what action you would like tack to perform then you can enter that value
immediately and avoid the menu display. When in doubt the question mark (?) is a good
character to type. A carriage return will execute the default action. These default
actions are designed to run all the standard tests.

When tack first comes up it will display some basic information about the terminal. Take
some time to verify this information. If it is wrong many of the subsequent tests will
fail. The most important item is the screen size. If the screen size is wrong there is
no point in proceeding. (home) and (clear) are also critical to the success of subsequent
tests. The values of (cr) (ind) (cub1) and (ht) may effect the tests if they are defined
incorrectly. If they are undefined tack will set them to reasonable defaults. The last
two entries on the display are the enquire and acknowledge strings. These strings are
taken from the user strings (u9) and (u8).

By now you must be wondering why the terminfo names are enclosed in parenthesis. This has
no profound meaning other than it makes them stand out. The tack program uses this
convention any time it displays a terminfo name. Remember tack is designed to rely on as
little of the terminfo entry as possible.

CREATING NEW ENTRIES

       Tack  has  a  number  of  tools  that  are  designed  to help gather information about the
       terminal.  Although these functions are not dependent on terminal type, you  may  wish  to
       execute tack with options -it.  This will turn off initialization and default the standard
       entries.

       These tools may be reached from the main menu by selecting the “tools” entry.

       Echo tool:  All data typed from the keyboard will be echoed back to the terminal.  Control
       characters  are  not translated to the up arrow format but are sent as control characters.
       This allows you to test an escape sequence and see what it actually does.   You  may  also
       elect  to  enable  hex  output  on echo tool this will echo the characters in hexadecimal.
       Once the test is running you may enter  the  “lines”  or  “columns”  keywords  which  will
       display  a  pattern  that  will  help  you determine your screen size.  A complete list of
       keywords will be displayed when the test starts.  Type “help” to  redisplay  the  list  of
       available commands.

       Reply  tool:  This tool acts much like the echo tool, but control characters that are sent
       from the terminal more than one character after a carriage return will be expanded to  the
       up arrow format.  For example on a standard ANSI terminal you may type:

                 CR ESC [ c

       and the response will be echoed as something like:

                 ^[ [ ? 6 c

       ANSI sgr display:  This test assumes you have an ANSI terminal.  It goes through attribute
       numbers 0 to 79, displaying each in turn and using that SGR  number  to  write  the  text.
       This  shows  you  which  of the SGR modes are actually implemented by the terminal.  Note:
       some terminals (such as Tektronix color) use the private use  characters  to  augment  the
       functionality  of  the  SGR command.  These private use characters may be interjected into
       the escape sequence by typing the character ( <, =, >, ? ) after the original display  has
       been shown.

       ANSI status reports:  This test queries the terminal in standard ANSI/VT-100 fashion.  The
       results of this test may help determine what options are supported by your terminal.

       ANSI character sets:  This test displays the character sets  available  on  a  ANSI/VT-100
       style  terminal.   Character  sets  on  a  real  VT-100  terminal are usually defined with
       smacs=\E(0 and rmacs=\E(B.  The first character after the escape defines  the  font  bank.
       The  second  character defines the character set.  This test allows you to view any of the
       possible combinations.  Private use character sets are defined by  the  digits.   Standard
       character sets are located in the alphabetic range.

VERIFYING AN EXISTING ENTRY

You can verify the correctness of an entry with the “begin testing” function. This entry
is the default action and will be chosen if you hit carriage return (or enter). This will
bring up a secondary menu that allows you to select more specific tests.

The general philosophy of the program is, for each capability, to send an appropriate test
pattern to the terminal then send a description of what the user should expect.
Occasionally (as when checking function-key capabilities) the program will ask you to
enter input for it to check.

If the test fails then you have the option of dynamically changing the terminfo entry and
re-running the test. This is done with the “edit terminfo” menu item. The edit submenu
allows you to change the offending terminfo entry and immediately retest the capability.
The edit menu lets you do other things with the terminfo, such as; display the entire
terminfo entry, display which caps have been tested and display which caps cannot be
tested. This menu also allows you to write the newly modified terminfo to disc. If you
have made any modifications to the terminfo tack will ask you if you want to save the file
to disc before it exits. The filename will be the same as the terminal name. After the
program exits you can run the tic(1M) compiler on the new terminfo to install it in the
terminfo data base.

CORRECTING PAD TIMINGS

Theory of Overruns and Padding
Some terminals require significant amounts of time (that is, more than one transmitted-
character interval) to do screen updates that change large portions of the screen, such as
screen clears, line insertions, line deletions, and scrolls (including scrolls triggered
by line feeds or a write to the lowest, right-hand-most cell of the screen).

If the computer continues to send characters to the terminal while one of these time-
consuming operations is going on, the screen may be garbled. Since the length of a
character transmission time varies inversely with transmission speed in cps, entries which
function at lower speeds may break at higher speeds.

Similar problems result if the host machine is simply sending characters at a sustained
rate faster than the terminal can buffer and process them. In either case, when the
terminal cannot process them and cannot tell the host to stop soon enough, it will just
drop them. The dropped characters could be text, escape sequences or the escape character
itself, causing some really strange-looking displays. This kind of glitch is called an
overrun.

In terminfo entries, you can attach a pad time to each string capability that is a number
of milliseconds to delay after sending it. This will give the terminal time to catch up
and avoid overruns.

If you are running a software terminal emulator, or you are on an X pseudo-tty, or your
terminal is on an RS-232C line which correctly handles RTS/CTS hardware flow control, then
pads are not strictly necessary. However, some display packages (such as ncurses(3X)) use
the pad counts to calculate the fastest way to implement certain functions. For example:
scrolling the screen may be faster than deleting the top line.

One common way to avoid overruns is with XON/XOFF handshaking. But even this handshake
may have problems at high baud rates. This is a result of the way XON/XOFF works. The
terminal tells the host to stop with an XOFF. When the host gets this character, it stops
sending. However, there is a small amount of time between the stop request and the actual
stop. During this window, the terminal must continue to accept characters even though it
has told the host to stop. If the terminal sends the stop request too late, then its
internal buffer will overflow. If it sends the stop character too early, then the
terminal is not getting the most efficient use out of its internal buffers. In a real
application at high baud rates, a terminal could get a dozen or more characters before the
host gets around to suspending transmission. Connecting the terminal over a network will
make the problem much worse.

(RTS/CTS handshaking does not have this problem because the UARTs are signal-connected and
the "stop flow" is done at the lowest level, without software intervention).

Timing your terminal
In order to get accurate timings from your terminal tack needs to know when the terminal
has finished processing all the characters that were sent. This requires a different type
of handshaking than the XON/XOFF that is supported by most terminals. Tack needs to send
a request to the terminal and wait for its reply. Many terminals will respond with an ACK
when they receive an ENQ. This is the preferred method since the sequence is short.
ANSI/VT-100 style terminals can mimic this handshake with the escape sequence that
requests “primary device attributes”.

ESC [ c

The terminal will respond with a sequence like:

ESC [ ? 1 ; 0 c

Tack assumes that (u9) is the enquire sequence and that (u8) is the acknowledge string. A
VT-100 style terminal could set u9=\E[c and u8=\E[?1;0c. Acknowledge strings fall into
two categories. 1) Strings with a unique terminating character and, 2) strings of fixed
length. The acknowledge string for the VT-100 is of the first type since it always ends
with the letter “c”. Some Tektronics terminals have fixed length acknowledge strings.
Tack supports both types of strings by scanning for the terminating character until the
length of the expected acknowledge string has arrived. (u8) should be set to some typical
acknowledge that will be returned when (u9) is sent.

Tack will test this sequence before running any of the pad tests or the function key
tests. Tack will ask you the following:

Hit lower case g to start testing...

After it sends this message it will send the enquire string. It will then read characters
from the terminal until it sees the letter g.

Testing and Repairing Pad Timings
The pad timings in distributed terminfo entries are often incorrect. One major motivation
for this program is to make it relatively easy to tune these timings.

You can verify and edit the pad timings for a terminal with the “test string capabilities”
function (this is also part of the “normal test sequence” function).

The key to determining pad times is to find out the effective baud rate of the terminal.
The effective baud rate determines the number of characters per second that the terminal
can accept without either handshaking or losing data. This rate is frequently less than
the nominal cps rate on the RS-232 line.

Tack uses the effective baud rate to judge the duration of the test and how much a
particular escape sequence will perturb the terminal.

Each pad test has two associated variables that can be tweaked to help verify the
correctness of the pad timings. One is the pad test length. The other is the pad
multiplier, which is used if the pad prefix includes “*”. In curses use, it is often the
first parameter of the capability (if there is one). For a capability like (dch) or (il)
this will be the number of character positions or lines affected, respectively.

Tack will run the pad tests and display the results to the terminal. On capabilities that
have multipliers tack will not tell you if the pad needs the multiplier or not. You must
make this decision yourself by rerunning the test with a different multiplier. If the
padding changes in proportion to the multiplier than the multiplier is required. If the
multiplier has little or no effect on the suggested padding then the multiplier is not
needed. Some capabilities will take several runs to get a good feel for the correct
values. You may wish to make the test longer to get more accurate results. System load
will also effect the results (a heavily loaded system will not stress the terminal as
much, possibly leading to pad timings that are too short).

NOTE

       The tests done at the beginning of the program are assumed to  be  correct  later  in  the
       code.   In  particular,  tack  displays  the  number of lines and columns indicated in the
       terminfo entry as part of its initial output.  If these values are wrong a large number of
       tests will fail or give incorrect results.

FILES

       tack.log    If logging is enabled then all characters written to the terminal will also be
                   written to the log file.  This gives you the ability to see how the tests were
                   performed.  This feature is disabled by default.

       term        If you make changes to the terminfo entry tack will save the new terminfo to a
                   file.  The file will have the same name as the terminal name.

BUGS

       If the screen size is incorrect, many of the tests will fail.

AUTHOR

       Concept,  design,  and  original  implementation  by  Daniel Weaver <dan.weaver@znyx.com>.
       Portions of the code and documentation are by Eric S. Raymond <esr@snark.thyrsus.com>.

                                                                                          tack(1)