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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 don't 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's 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 informa-
tion 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 sub-
sequent 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 ack-
nowledge 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 termi-
nal 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 termi-
nal. 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 imple-
mented by the terminal. Note: some terminals (such as Tek-
tronix color) use the private use characters to augment the
functionality of the SGR command. These private use charac-
ters 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 capabil-
ity, 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 sub-
menu 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 send-
ing characters at a sustained rate faster than the terminal
can buffer and process them. In either case, when the ter-
minal cannot process them and can't 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 calcu-
late 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 handshak-
ing. 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 charac-
ter too early, then the terminal is not getting the most
efficient use out of its internal buffers. In a real appli-
cation 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 termi-
nal 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 ter-
minals 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 charac-
ter 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 fol-
lowing:
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 effec-
tive baud rate of the terminal. The effective baud rate
determines the number of characters per second that the ter-
minal 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 per-
turb 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 multi-
plier, which is used if the pad prefix includes `*'. In
curses use, it is often the first parameter of the capabil-
ity (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 propor-
tion to the multiplier than the multiplier is required. If
the multiplier has little or no effect on the suggested pad-
ding 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 writ-
ten 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 dis-
abled 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.
SEE ALSO
terminfo(5), ncurses(3X), tic(1m), infocmp(1m). You should
also have the documentation supplied by the terminal
manufacturer.
BUGS
If the screen size is incorrect, many of the tests will
fail.
AUTHOR
Concept, design, and original implementation by Daniel
Weaver <danw@znyx.com>. Portions of the code and documenta-
tion are by Eric S. Raymond <esr@snark.thyrsus.com>.
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