readme.buz

讲述linux的初始化过程

Iomega Buz Driver for Linux
===========================

by Rainer Johanni <[e-mail]>

Compiling and Loading the Driver
================================

You must run a 2.2.x kernel in order to use this driver.

To compile the driver, just type make.

Besides the files in this directory, the driver needs the
'videodev' and the 'i2c' module from the Linux kernel.
In order to get these modules available, enable module support
for VIDEODEV and BTTV (which implies i2c) in your kernel
configuration. You find these devices in the menu
"Character Devices" in your Kernel Configuration.

Before you load the driver you must have a video device
at major device node 81. If you don't have it yet, do the
following (as root!):

cd /dev
mknod video0 c 81 0
ln -s video0 video

Edit the 'update' script if you want to give the driver
special options and then type (as root)

./update

to insert all the necessary modules into the kernel.

If you want to make full use of the Video for Linux uncompressed
grabbing facilities, you must either

- obtain and install the "big_physarea patch" for your kernel and
  set aside the necessary memory during boot time.
  There seem to be several versions of this patch against
  various kernel versions floating around in the net,
  you may obtain one e.g. from:
  http://www.polyware.nl/~middelin/patch/bigphysarea-2.2.1.tar.gz
  You also have to compile your driver AFTER installing that patch
  in order to get it working

  or

- start your kernel with the mem=xxx option, where xxx is your
  real memory minus the memory needed for the buffers.
  For doing this add an entry in lilo.conf (if you use lilo):
    append "mem=xxxM"
  or add a line in your linux.par file (if you use loadlin):
    mem=xxxM

The second method is by far easier, however it is dangerous
if more than one driver at a time has the idea to use the memory
leftover by setting the mem=xxx parameter below the actual
memory size.

Read also below how to use this memory!



Driver Options
==============

You are able to customize the behavior of the driver by giving
it some options at start time.

default_input, default_norm
---------------------------

As soon as the driver is loaded, the Buz samples video signals
from one of its input ports and displays it on its output.
The driver uses the Composite Input and the video norm PAL for this.
If you want to change this default behavior, set default_input=1
(for S-VHS input) or default_norm=1 for NTSC.

v4l_nbufs, v4l_bufsize
----------------------

In order to make to make full use of the Video for Linux picture
grabbing facilities of the driver (which are needed by many
Video for Linux applications), the driver needs a set of
physically contiguous buffers for grabbing. These parameters
determine how many buffers of which size the driver will
allocate at open (the open will fail if it is unable to do so!).

These values do not affect the MJPEG grabbing facilities of the driver,
they are needed for uncompressed image grabbing only!!!

v4l_nbufs is the number of buffers to allocate, a value of 2 (the default)
should be sufficient in almost all cases. Only special applications
(streaming captures) will need more buffers and then mostly the
MJPEG capturing features of the Buz will be more appropriate.
So leave this parameter at it's default unless you know what you do.

The things for v4l_bufsize are more complicated:
v4l_bufsize is set by default to 128 [KB] which is the maximum
amount of physically contiguous memory Linux is able to allocate
without kernel changes. This is sufficient for grabbing 24 bit color images
up to sizes of approx. 240x180 pixels (240*180*3 = 129600, 128 KB = 131072).

In order to be able to capture bigger images you have either to
- obtain and install the "big_physarea patch" and set aside
  the necessary memory during boot time or
- start your kernel with the mem=xxx option, where xxx is your
  real memory minus the memory needed for the buffers.
In that case, useful settings for v4l_bufsize are
- 1296 [Kb] for grabbing 24 bit images of max size 768*576
- 1728 [Kb] for 32bit images of same size (4*768*576 = 1728 Kb!)
You may reduce these numbers accordingly if you know you are only
grabbing 720 pixels wide images or NTSC images (max height 480).

In some cases it may happen that Linux isn't even able to obtain
the default 128 KB buffers. If you don't need uncompressed image
grabbing at all, set v4l_bufsize to an arbitrary small value (e.g. 4)
in order to be able to open the video device.

vidmem
------

The video mem address of the video card.
The driver has a little database for some videocards
to determine it from there. If your video card is not in there
you have either to give it to the driver as a parameter
or set in in a VIDIOCSFBUF ioctl

The videocard database is contained in the file "videocards.h"
Gernot Ziegler wants to keep an actual version of that file.
If your card is not contained in that file, look at
http://www.lysator.liu.se/~gz/buz/ for an actual version of
"videocards.h".

triton, natoma
--------------

The driver tries to detect if you have a triton or natome chipset
in order to take special measures for these chipsets.
If this detection fails but you are sure you have such a chipset,
set the corresponding variable to 1.
This is a very special option and may go away in the future.



Programming interface
=====================

This driver should be fully compliant to Video for Linux, so all
tools working with Video for Linux should work with (hopefully)
no problems.

A description of the Video for Linux programming interface can be found at:
http://roadrunner.swansea.linux.org.uk/v4lapi.shtml

Besides the Video for Linux interface, the driver has a "proprietary"
interface for accessing the Buz's MJPEG capture and playback facilities.

The ioctls for that interface are as follows:

BUZIOC_G_PARAMS
BUZIOC_S_PARAMS

Get and set the parameters of the buz. The user should always
do a BUZIOC_G_PARAMS (with a struct buz_params) to obtain the default
settings, change what he likes and then make a BUZIOC_S_PARAMS call.
A typical application should at least set the members
input, norm and decimation of the struct buz_params.
For a full description of all members see "buz.h"

BUZIOC_REQBUFS

Before being able to capture/playback, the user has to request
the buffers he is wanting to use. Fill the structure
buz_requestbuffers with the size (recommended: 256*1024) and
the number (recommended 32 up to 256). There are no such restrictions
as for the Video for Linux buffers, you should LEAVE SUFFICIENT
MEMORY for your system however, else strange things will happen ....
On return, the buz_requestbuffers structure contains number and
size of the actually allocated buffers.
You should use these numbers for doing a mmap of the buffers
into the user space.
The BUZIOC_REQBUFS ioctl also makes it happen, that the next mmap
maps the MJPEG buffer instead of the V4L buffers.

BUZIOC_QBUF_CAPT
BUZIOC_QBUF_PLAY

Queue a buffer for capture or playback. The first call also starts
streaming capture. When streaming capture is going on, you may
only queue further buffers or issue syncs until streaming
capture is switched off again with a argument of -1 to
a BUZIOC_QBUF_CAPT/BUZIOC_QBUF_PLAY ioctl.

BUZIOC_SYNC

Issue this ioctl when all buffers are queued. This ioctl will
block until the first buffer becomes free for saving its
data to disk (after BUZIOC_QBUF_CAPT) or for reuse (after BUZIOC_QBUF_PLAY).

BUZIOC_G_STATUS

Get the status of the input lines (video source connected/norm).
This ioctl may be subject to change.





See the examples directory delivered with this driver
for actual coding examples!