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.\" gsc.4 - manual page for the scanner device driver `gsc'
.\"
.\"
.\" Copyright (c) 1995 Gunther Schadow.  All rights reserved.
.\"
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.\"    must display the following acknowledgement:
.\"	This product includes software developed by Gunther Schadow.
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.\" $FreeBSD: src/share/man/man4/man4.i386/gsc.4,v 1.12.2.7 2001/12/17 11:30:13 ru Exp $
.\"
.Dd January 9, 1995
.Dt GSC 4 i386
.Os
.Sh NAME
.Nm gsc
.Nd a device driver for a handy scanner
.Sh SYNOPSIS
.In machine/gsc.h
.Pp
.Cd Minor number bits: Ar uu d g p ...
.Bl -tag -width "uu " -compact -offset indent
.It Ar uu
unit gsc0 .. gsc3
.It Ar d
selects logging of
.Em debug
messages
.It Ar g
selects
.Em bitmap
vs.
.Em graymap
output
.It Ar p
selects
.Em raw
vs. portable
.Em pnm
output
.El
.Sh DESCRIPTION
The
.Nm
character device driver currently handles only the
Genius GS-4500 handy scanner.
It operates in pure DMA modes, although
the hardware could be set up to work with irq.
I had neither enough
documentation nor experience in writing interrupt driven device
drivers.
.Pp
The device can operate at four different
.Em resolutions :
100, 200,
300 and 400dpi.
It produces a simple bitmap with the most significant
bit at the left side.
The driver can optionally output the famous and
likely simple portable bitmap file format
.Xr pbm 5
by Jef Poskanzer.
Thus the scans can easily processed by any graphic package around
.Xr ( xpaint 1 ,
.Xr xv 1 ,
.Xr xli 1
only to name some of them ...).  In
.Em raw
mode a
bit which is set means a black pixel because the scanner detects black
points on white paper.
On the other hand, because pnm format describes
intensities of electron beams in video screens a set bit in
.Em pbm
mode means a white pixel.
.Pp
The
.Em width
of the output bitmap is fixed as given by the
resolution value.
However, the
.Em height
of the bitmap must be
supplied in
.Em pnm
mode since the driver must know at what time the
.Sq end-of-file
shall be reached.
With this feature you are able to
directly copy the scanner output into a pbm file with
.Xr cat 1 .
Of course you can obtain a similar effect by using
.Xr dd 1
with the driver in
.Em raw
mode.
.Pp
The
.Em graymap
output mode is not yet implemented into the driver.
It is even questionable if external programs would not do this job
better thereby not counting to the size of the kernel.
Even though, I
do not know of tools which produce a graymap from a halftone bitmap.
.Pp
The ioctl requests that are served by
.Nm
are listed below.
There is a utility, called
.Xr sgsc 1 ,
that provides access to these
requests from within shell.
.Bl -tag -width Ds
.It Dv GSC_SRES Vt int
Set the
.Em resolution
value.
If this call is made after the first
read access to the device there will be no effect unless the device is
closed and opened again.
.It Dv GSC_GRES Vt int
Get current resolution in dots per inch (dpi).
.It Dv GSC_SRESSW Vt void
Set resolution value from selector switch.
The driver must be in an
open though untouched state otherwise the request will fail and
.Xr errno 2
is set to
.Er EBUSY .
.It Dv GSC_SWIDTH Vt int
Set the
.Em width
of the bitmap.
Actually, this is an alternative
way of setting the resolution, since any allowed resolution matches
exactly one width.
Allowed are listed in the table below.
.Bl -tag -width resolution -compact -offset indent
.It resolution
width
.It 100 dpi
424 pixels
.It 200 dpi
840 pixels
.It 300 dpi
1264 pixels
.It 400 dpi
1648 pixels
.It ?
1696 pixels
.It ?
2544 pixels
.It ?
3648 pixels
.El
.Pp
Values which are not reported in the above table will cause the ioctl
call to fail with
.Xr errno 2
set to
.Er EINVAL .
.Pp
As you can see, there are width values > 1696.
This does, however, not
mean that you can obtain scanned lines longer than the width of your
scanner or by higher resolutions.
Actually, the resolution is selected
by only by the hardware switch.
Any line that is longer than what is
defined for the actual resolution will be undefined (usually white) on
the right part that is exceeding the standard line.
.It Dv GSC_GWIDTH Vt int
Get current width of the bitmap in pixels.
.It Dv GSC_SHEIGHT Vt int
Set the
.Em height
of the bitmap in
.Em pnm
mode.
This is actually
a limit on the amount of lines scannable after the first read
operation.
When the limit is reached read will return 0. However, the
device is turned off only when a close is performed (either
explicitly or implicitly on exit of the calling process).
.It Dv GSC_GHEIGHT Vt int
Get the current height of the bitmap.
.It Dv GSC_SBLEN Vt int
Set the length of the buffer used internally to do the DMA transfer.
The buffer length is supplied in lines of the bitmap.
Since the buffer
size limit is (currently) 0x3000 bytes the maximum number of lines
allowed will vary with the width of each line.
This upper limit is
checked before it overwrites the current value and passes an
.Er ENOMEM
in the
.Xr errno 2
variable.
However, since the bitmap width can change
after a buffer length was selected a read request may fail with
.Er ENOMEM
if the buffer length turns out too high.
It is generally wise to
choose long buffers rather than go save in order to obtain better
output.
.It Dv GSC_GBLEN Vt int
Get the current buffer length in lines.
.It Dv GSC_SBTIME Vt int
Set the timeout for the completion of reading one buffer.
Since a
handy scanner is a human/computer interface timeout values are usually
higher than those of a flat scanner.
Default is 15 seconds.
After
timeout is reached the read operation will fail with
.Er EBUSY .
Note that
the timeout timer starts anew for each buffer to be read and thus does
not cause you to scan faster for longer images.
BLEN/BTIME is similar
as MIN/TIME in
.Xr termios 4 .
.It Dv GSC_GBTIME Vt int
Get the current buffer timeout.
.El
.Pp
All ioctl requests that modify a parameter except
.Dv GSC_SBTIME
do not
have an effect on an ongoing scan process, i.e. after the first read
request that follows open.
You must close the device and open it again
for the new selections to take effect.
Consequently, the selections
are not reset when you close or open the device.
.Pp
Similarly, requests that read a value do not report the value that is
used for the ongoing scan process.
The values needed during the scan
process are saved when it starts and thus are not accessed by ioctl
requests.
.Pp
The BTIME value does, however, have an immediate effect on the ongoing
scan.
Thus the timeout can for example be set to long until the user
starts scanning.  It can then be set to a short amount to react
(nearly) immediately when the user stops.
Note that the user should be
left time to at least fill one buffer without having to haste.
.Pp
Note that the
.Em pbm
versus
.Em raw
mode selection is done by the
minor number not by ioctl requests.
In
.Em raw
mode the selected
height of the bitmap will have no effect.
.Sh FILES
.Bl -tag -width /dev/gsc0pd
.It Pa /dev/gsc0
device node for
.Em raw
output, has minor number 0.
.It Pa /dev/gsc0d
device node for
.Em raw
output emitting
.Em debug
messages if the
GSCDEBUG option was given at compile time, has minor number 32.
.It Pa /dev/gsc0p
device node for output in
.Em pbm
file format, has minor number 8.
.It Pa /dev/gsc0pd
device node for
.Em pbm
and
.Em debug
mode, has minor number 40.
.El
.Sh EXAMPLES
.Bd -literal -offset indent
dd if=/dev/gsc0 of=rawfile bs=(width/8) count=(height)

cat /dev/gsc0p > pbmfile
.Ed
.Sh DIAGNOSTICS
.Bl -tag -width Cd
.It GSCDEBUG
When you define this name as an `option' in the kernel configuration
you can get debug output if you access the driver with a minor number
whose debug bit (i.e. bit 5 out of 7) is set.
.El
.Sh SEE ALSO
.Xr cat 1 ,
.Xr dd 1 ,
.Xr pbmtopgm 1 Pq Pa pkgsrc/graphics/netpbm ,
.Xr sgsc 1 ,
.Xr close 2 ,
.Xr intro 2 ,
.Xr ioctl 2 ,
.Xr open 2 ,
.Xr read 2 ,
.Xr termios 4 ,
.Xr pbm 5 Pq Pa pkgsrc/graphics/netpbm ,
.Xr pnm 5 Pq Pa pkgsrc/graphics/netpbm
.Sh AUTHORS
.An Gunther Schadow Aq gusw@fub46.zedat.fu-berlin.de
.Sh BUGS
Even though the scanner device has a little switch by which you should
be able to select one of the four resolution modes, I could not yet
determine how to read its status.
Unless this is not fixed the driver
depends on the value passed by means of
.Xr ioctl 2
which need not match
what is selected by the hardware.