scope.1

在linux下多媒体开发实例linux下多媒体开发

.\" This file Copyright (C) 1994-95 Jeff Tranter
.\" ([e-mail])
.\" It may be distributed under the GNU Public License, version 2, or
.\" any higher version.  See section COPYING of the GNU Public license
.\" for conditions under which this file may be redistributed.
.TH SCOPE 1 "6 Oct 1995" "Linux" "User Commands"
.SH NAME
scope \- Software Oscilloscope
.SH SYNOPSIS

scope -r<rate> -m<mode> -c<colour> -d<dma divisor> -t<trigger> -p -l
-g -v -i<file> -j<joystick-device>

.SH DESCRIPTION

.B Scope
is a simple software emulation of an oscilloscope. It graphically
displays voltage as a function of time. The input is via a sound
card using the kernel sound device /dev/dsp.

The svgalib library is used to implement a real-time waveform
display.

.PP
.SH "COMMAND\-LINE OPTIONS"
.TP 0.5i
.B -r <rate>
Specify the sampling rate in samples per second. The upper and lower
limits depend on the sound card you have; the default is
8000.

.TP 0.5i
.B -m <mode>
Sets the graphics to use. The modes are listed in the svgalib header
file "vga.h". The default mode is 4 -- 640x480 with 16 colours. If
you select a graphics mode with a vertical resolution of less than 255
you may not be able to display the entire waveform. Don't use graphics
modes that are not supported by your monitor.

.TP 0.5i
.B -c <colour>
Sets the trace colour. The colours available depend on the graphics
mode selected. The default is 2 -- green (just like a real
oscilloscope).

.TP 0.5i
.B -d <dma divisor>
Sets the divisor for DMA buffer size. Valid numbers are 1, 2, or 4.
The kernel sound driver will divide it's DMA buffer by this factor.
The default value of 4 usually gives the fastest display rate.

.TP 0.5i
.B -t <trigger>
Sets the trigger level. The scope will wait until it receives a signal
greater than this level. It should be in the range 0 .. 255. The
default is to run without waiting for a trigger. Note that the top of
the display is 0, the bottom is 255, and the midpoint is 128.

You cannot quit using "Q" while waiting for a trigger (use Control-C
instead). You cannot change the trigger level unless it was enabled
from the command line.

.TP 0.5i
.B -p (point mode)
.TP 0.5i
.B -l (line mode)
These options are mutually exclusive. In point mode (-p) the graph is
shown as individual data points. In line mode (-l) the points are
joined using lines. Line mode gives a better display, but is somewhat
slower than point mode. The default is line mode.

.TP 0.5i
.B -g
Enables a graticule (a frame around the waveform). This slows down the
display a little bit. If trigger is enabled, a small tick mark is
shown on the graticule corresponding to the trigger level.

.TP 0.5i
.B -v
Runs
.B scope
in verbose mode. Extra information is displayed on standard
output.

.TP 0.5i
.B -i <file>
Instructs
.B scope
to read data from a file rather than /dev/dsp. The input must be a
series of raw, unsigned, 8-bit, linear sound data bytes. A utility
such as
.B Sox
can be used to convert sound files to this format. The sampling rate
and DMA divisor options are meaningless if the option is used. If you
want, you can plot non-sound data from a file such as /vmlinux.

.TP 0.5i
.B -j <joystick-device>
Instructs
.B scope
to read data from a joystick device rather than /dev/dsp. Only the
vertical axis is used and the values are scaled by an arbitrary value.

.PP
.SH "RUN\-TIME CONTROLS"
.PP

While the program is running, it accepts the following single key commands:

.PP
q/Q - quit the program
.PP
R/r - increase/decrease sampling rate 10%
.PP
T/t - increase/decrease trigger level 10 units
.PP
l/p - go to line/point mode
.PP
C/c - increment/decrement colour used
.PP
G/g - enable/disable graticule
.PP
<space> - pause the display until another key is pressed
.PP
D/d - write screen dump in X bitmap format to file scope.xbm

.SH EXAMPLES
.TP 0.5i
.B scope -r 44000 -l -v

This runs
.B scope
at a 44kHz sampling rate, in line mode, with verbose output.

.SH PORTABILITY
.B Scope
was written specifically for Linux, and uses the Linux sound driver
and svgalib plotting routines. Obviously you need a sound card, VGA
graphics, and the Linux kernel sound drivers.

.SH BUGS/LIMITATIONS
.PP

This should be considered ALPHA software.  It was basically written
for fun rather than as a useful tool. It has a few known bugs, and it
really needs a better user interface. Unfortunately, adding anything
to the display (controls, etc...) would slow it down considerably.

Because it uses svgalib,
.B scope
must be run as root or setuid to root.

The display will probably not be able to keep up at higher sampling
rates, depending on your sound card, graphics card, and processor
speed. No floating point math is used, so a math coprocessor doesn't
make any difference.

You have to use an external mixer program to select the input source
device, level, etc... (if you use a microphone the default should
work).

When displaying data from a file,
.B Scope
does not know what the sampling rate is. The data is graphed as fast
as possible. If this is too fast, you need to upgrade to a slower
computer.

I can think of a bunch of enhancements that might be fun to add: 16
bit and stereo sampling, single shot mode, envelope mode, spectrum
analyzer (FFT) mode, graphical controls (mouse), graticule, and
storage mode (with waveform save/load), but it would probably run too
slowly.

.SH AUTHOR
.B Scope
was written by Jeff Tranter ([e-mail]) and is released
under the conditions of the GNU General Public License.  See the file
COPYING and notes in the source code for details.