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