.TH TIMEPIC 1
.SH NAME
timepic \- troff preprocessor for drawing timing diagrams
.SH SYNOPSIS
.B timepic
[
.I files
]
.SH DESCRIPTION
.I Timepic
is a 
.IR pic (1)
and
.IR troff (1)
preprocessor for drawing timing diagrams.
.I Timepic
code is contained between
.B .TPS
and
.B .TPE
lines:
.IP
.EX
\&.TPS \f2width\fP \f2row-height\fP
\f2statement-list\fP
\&.TPE
.EE
.PP
There are two types of
.I timepic
statements: variable definitions and signal definitions.
Variables are defined with the syntax
.IP
.EX
\f2var\fP = \f2expr\fP;
.EE
.PP
where 
.I expr
is an arithmetic expression involving floating-point constants and previously defined variables.
Currently only basic arithmetic (\fB+\fR, \fB-\fR, \fB*\fR and \fB/\fR) is supported.
Signals are defined with the syntax
.IP
.EX
\f2name\fP \f2events\fP ;
.EE
.PP
where
.I name
is a name that must be quoted unless it's a valid symbol.
\f2Events\fR is a list consisting of the following things:
.TP
\(bu
The current time can be set using an arithmetic expression, that may be followed by a symbol interpreted as a unit.
For instance if you defined 
.B "μs = 1000;"
then 
.B 1μs
and
.B "(x+2)*3μs"
are both valid time expressions.
Note that
.B x+2μs
is interpreted as 
.B (x+2)μs
which may or may not be intended behaviour.
.IP
A time expression can be preceded by \fP+\fR to mark it as relative to the previous time.
The first time is zero.
.IP
A time expression can be followed by a symbol name in square brackets.
The symbol is then defined with the time.
.TP
\(bu
An expression of the form \fP:\fIname\fR creates an `event' at the current time, changing the value of the signal to \fIname\fR.
\fIname\fR can be a symbol (which is not evaluated), a numerical constant or a string in single quotes.
The values
.BR 0 ,
.BR 1 ,
.BR x
and
.B z
have special meaning, unless they are quoted.
.TP
\(bu
A pipe symbol
.B |
draws a vertical dashed line at the next event.
.TP
\(bu
An expression of the form
.IB expr { events }
evaluates the expression, rounded to the nearest integer, and then repeats the events the specified number of times.
It is illegal if the expression evaluates to a negative number.
It is also illegal to use absolute times in the events list.
It is however legal to nest this construct.
.SH EXAMPLES
.IP
.EX
\&.TPS 6 0.4
c=5;
clk +5{:1 +.5c:0 +.5c};
data :x 2.3c:DQ 4c|:x;
valid :0 2.3c:1 4c:0;
ready :0 3.6c:1 4c:0;
\&.TPE
.EE
.SH FILES
.B /sys/src/cmd/timepic.c
.SH "SEE ALSO"
.IR troff (1),
.IR pic (1)
.SH BUGS
Yes.