asc -- device driver for a GI1904-based hand scanner
device asc 1
The asc character device driver currently handles the GI1904-based hand
scanner (e.g. Trust Amiscan Grey). It uses DMA and interrupts. Up to 50
lines of scanned input data are buffered in the driver.
The device can operate at four different resolutions: 100, 200, 300 and
400 dots per inch. It produces a simple bitmap with the most significant
bit at the left side. The driver can optionally output the simple portable
bitmap file format pbm(5); thus the scans can easily processed by
most graphics packages.
The width of the output bitmap is fixed as given by the resolution value.
However, the height of the bitmap must be supplied when in pbm(5) mode,
since the driver must know at what time the `end-of-file' shall be
reached. The default is to produce a square image; i.e., height equals
width. With this feature one is able to directly copy the scanner output
into a pbm(5) file using cat(1). One can obtain a similar effect by
using dd(1) with the driver in raw mode.
The ioctl(2) commands applicable to asc are listed below. The sasc(1)
provides user-level access to these commands.
ASC_GRES (int) Get current resolution in dots per inch (dpi).
ASC_GWIDTH (int) Get current width of the bitmap in pixels.
ASC_SHEIGHT (int) Set the height of the bitmap in pbm(5) 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 the
last open file descriptor is closed.
ASC_GHEIGHT (int) Get the current height of the bitmap.
ASC_SBLEN (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. An ENOMEM error is returned if the
requested length would exceed this limit.
ASC_GBLEN (int) Get the current buffer length in lines.
ASC_SBTIME (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;
the default is 15 seconds. After timeout is reached
the read operation will fail with EBUSY. Note that the
timeout timer starts anew for each buffer to be read and
thus reducing it does not result in faster scans for longer
ASC_GBTIME (int) Get the current buffer timeout.
All ioctl() requests that modify a parameter except ASC_SBTIME do not
have an effect on an ongoing scan process. The user must close the
device and open it again for the new selections to take effect. Consequently,
the selections are not reset when the device is opened or
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()
The ASC_SBTIME value does, however, have an immediate effect on the ongoing
scan. Thus the timeout can, for example, be set to a large value
until the user starts scanning, and then set to a small value to react
(nearly) immediately when the user stops.
Note that the pbm(5) versus raw mode selection is done by the minor number,
not by ioctl() requests. In raw mode, the selected height of the
bitmap will have no effect.
/dev/asc0 device node for raw output
/dev/asc0d device node for raw output, emitting debug messages if the
ASCDEBUG option was given in the kernel configuration file
/dev/asc0p device node for output in pbm(5) file format
/dev/asc0pd device node for pbm(5) and debug mode
Ioctl support is not working yet.
The asc driver was written by Luigi Rizzo.
The asc driver first appeared in FreeBSD 2.1.
FreeBSD 5.2.1 January 19, 1995 FreeBSD 5.2.1 [ Back ]