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SunOS 5.5 Ioctl Requests termio(7I)

Comparison of the

different cases of

MIN, TIME

interaction

Some points to note about MIN and TIME:

1. In the following explanations,note that the interactions of MIN and TIME are

not symmetric. For example, when MIN > 0 and TIME =0,TIME has no effect.

However, in the opposite case, where MIN = 0 and TIME > 0, both MIN and

TIME play a role in that MIN is satisﬁed with the receipt of a single character.

2. Also note that in case A (MIN >0,TIME > 0), TIME represents an intercharacter

timer, whereas in case C (MIN =0,TIME > 0), TIME represents a read timer.

These two points highlight the dual purpose of the MIN/TIME feature. Cases A and B,

where MIN > 0, exist to handle burst mode activity (for example, ﬁle transfer programs),

where a program would like to process at least MIN characters at a time. In case A, the

intercharacter timer is activated by a user as a safety measure; in case B, the timer is

turned off.

Cases C and D exist to handle single character, timed transfers. These cases are readily

adaptable to screen-based applications that need to know if a character is present in the

input queue before refreshing the screen. In case C, the read is timed, whereas in case D,

it is not.

Another important note is that MIN is always just a minimum. It does not denote a

record length. For example, if a program does a read of 20 bytes, MIN is 10, and 25 char-

acters are present, then 20 characters will be returned to the user.

Writing characters When one or more characters are written, they are transmitted to the terminal as soon as

previously written characters have ﬁnishedtyping. Input characters are echoed as they

are typed if echoing has been enabled. If a process produces characters more rapidly

than they can be typed, it will be suspended when its output queue exceeds some limit.

When the queue is drained down to some threshold, the program is resumed.

Special Characters Certain characters have special functions on input. These functions and their default

character values are summarized as follows:

INTR (CTRL-C or ASCII ETX) generates a SIGINT signal. SIGINT is sent to all fre-

quent processes associated with the controlling terminal. Normally,

each such process is forced to terminate, but arrangements may be made

either to ignore the signal or to receive a trap to an agreed upon location.

(See signal(5)).

QUIT (CTRL- or ASCII FS) generates a SIGQUIT signal. Its treatment is identi-

cal to the interrupt signal except that, unless a receiving process has

made other arrangements, it will not only be terminated but a core

image ﬁle (called core) will be created in the current working directory.

ERASE (DEL) erases the preceding character. It does not erase beyond the start

of a line, as delimited by a NL, EOF, EOL,orEOL2 character.

WERASE (CTRL-W or ASCII ETX) erases the preceding “word”. It does not erase

beyond the start of a line, as delimited by a NL, EOF, EOL,orEOL2 char-

acter.

KILL (CTRL-U or ASCII NAK) deletes the entire line, as delimited by aNL, EOF,

modiﬁed 30 May 1995 7I-349

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