• Main Page
  • Related Pages
  • Modules
  • Data Structures
  • Files
  • File List
  • Globals

libavdevice/dv1394.h

Go to the documentation of this file.
00001 /*
00002  * DV input/output over IEEE 1394 on OHCI chips
00003  *   Copyright (C)2001 Daniel Maas <dmaas@dcine.com>
00004  *     receive, proc_fs by Dan Dennedy <dan@dennedy.org>
00005  *
00006  * based on:
00007  *   video1394.h - driver for OHCI 1394 boards
00008  *   Copyright (C)1999,2000 Sebastien Rougeaux <sebastien.rougeaux@anu.edu.au>
00009  *                          Peter Schlaile <udbz@rz.uni-karlsruhe.de>
00010  *
00011  * This file is part of FFmpeg.
00012  *
00013  * FFmpeg is free software; you can redistribute it and/or
00014  * modify it under the terms of the GNU Lesser General Public
00015  * License as published by the Free Software Foundation; either
00016  * version 2.1 of the License, or (at your option) any later version.
00017  *
00018  * FFmpeg is distributed in the hope that it will be useful,
00019  * but WITHOUT ANY WARRANTY; without even the implied warranty of
00020  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
00021  * Lesser General Public License for more details.
00022  *
00023  * You should have received a copy of the GNU Lesser General Public
00024  * License along with FFmpeg; if not, write to the Free Software
00025  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
00026  */
00027 
00028 #ifndef AVDEVICE_DV1394_H
00029 #define AVDEVICE_DV1394_H
00030 
00031 #define DV1394_DEFAULT_CHANNEL 63
00032 #define DV1394_DEFAULT_CARD    0
00033 #define DV1394_RING_FRAMES     20
00034 
00035 #define DV1394_WIDTH  720
00036 #define DV1394_NTSC_HEIGHT 480
00037 #define DV1394_PAL_HEIGHT 576
00038 
00039 /* This is the public user-space interface. Try not to break it. */
00040 
00041 #define DV1394_API_VERSION 0x20011127
00042 
00043 /* ********************
00044    **                **
00045    **   DV1394 API   **
00046    **                **
00047    ********************
00048 
00049    There are two methods of operating the DV1394 DV output device.
00050 
00051    1)
00052 
00053    The simplest is an interface based on write(): simply write
00054    full DV frames of data to the device, and they will be transmitted
00055    as quickly as possible. The FD may be set for non-blocking I/O,
00056    in which case you can use select() or poll() to wait for output
00057    buffer space.
00058 
00059    To set the DV output parameters (e.g. whether you want NTSC or PAL
00060    video), use the DV1394_INIT ioctl, passing in the parameters you
00061    want in a struct dv1394_init.
00062 
00063    Example 1:
00064          To play a raw .DV file:   cat foo.DV > /dev/dv1394
00065          (cat will use write() internally)
00066 
00067    Example 2:
00068            static struct dv1394_init init = {
00069               0x63,        (broadcast channel)
00070               4,           (four-frame ringbuffer)
00071               DV1394_NTSC, (send NTSC video)
00072               0, 0         (default empty packet rate)
00073            }
00074 
00075            ioctl(fd, DV1394_INIT, &init);
00076 
00077            while(1) {
00078                   read( <a raw DV file>, buf, DV1394_NTSC_FRAME_SIZE );
00079                   write( <the dv1394 FD>, buf, DV1394_NTSC_FRAME_SIZE );
00080            }
00081 
00082    2)
00083 
00084    For more control over buffering, and to avoid unnecessary copies
00085    of the DV data, you can use the more sophisticated the mmap() interface.
00086    First, call the DV1394_INIT ioctl to specify your parameters,
00087    including the number of frames in the ringbuffer. Then, calling mmap()
00088    on the dv1394 device will give you direct access to the ringbuffer
00089    from which the DV card reads your frame data.
00090 
00091    The ringbuffer is simply one large, contiguous region of memory
00092    containing two or more frames of packed DV data. Each frame of DV data
00093    is 120000 bytes (NTSC) or 144000 bytes (PAL).
00094 
00095    Fill one or more frames in the ringbuffer, then use the DV1394_SUBMIT_FRAMES
00096    ioctl to begin I/O. You can use either the DV1394_WAIT_FRAMES ioctl
00097    or select()/poll() to wait until the frames are transmitted. Next, you'll
00098    need to call the DV1394_GET_STATUS ioctl to determine which ringbuffer
00099    frames are clear (ready to be filled with new DV data). Finally, use
00100    DV1394_SUBMIT_FRAMES again to send the new data to the DV output.
00101 
00102 
00103    Example: here is what a four-frame ringbuffer might look like
00104             during DV transmission:
00105 
00106 
00107          frame 0   frame 1   frame 2   frame 3
00108 
00109         *--------------------------------------*
00110         | CLEAR   | DV data | DV data | CLEAR  |
00111         *--------------------------------------*
00112                    <ACTIVE>
00113 
00114         transmission goes in this direction --->>>
00115 
00116 
00117    The DV hardware is currently transmitting the data in frame 1.
00118    Once frame 1 is finished, it will automatically transmit frame 2.
00119    (if frame 2 finishes before frame 3 is submitted, the device
00120    will continue to transmit frame 2, and will increase the dropped_frames
00121    counter each time it repeats the transmission).
00122 
00123 
00124    If you called DV1394_GET_STATUS at this instant, you would
00125    receive the following values:
00126 
00127                   n_frames          = 4
00128                   active_frame      = 1
00129                   first_clear_frame = 3
00130                   n_clear_frames    = 2
00131 
00132    At this point, you should write new DV data into frame 3 and optionally
00133    frame 0. Then call DV1394_SUBMIT_FRAMES to inform the device that
00134    it may transmit the new frames.
00135 
00136    ERROR HANDLING
00137 
00138    An error (buffer underflow/overflow or a break in the DV stream due
00139    to a 1394 bus reset) can be detected by checking the dropped_frames
00140    field of struct dv1394_status (obtained through the
00141    DV1394_GET_STATUS ioctl).
00142 
00143    The best way to recover from such an error is to re-initialize
00144    dv1394, either by using the DV1394_INIT ioctl call, or closing the
00145    file descriptor and opening it again. (note that you must unmap all
00146    ringbuffer mappings when closing the file descriptor, or else
00147    dv1394 will still be considered 'in use').
00148 
00149    MAIN LOOP
00150 
00151    For maximum efficiency and robustness against bus errors, you are
00152    advised to model the main loop of your application after the
00153    following pseudo-code example:
00154 
00155    (checks of system call return values omitted for brevity; always
00156    check return values in your code!)
00157 
00158    while( frames left ) {
00159 
00160     struct pollfd *pfd = ...;
00161 
00162     pfd->fd = dv1394_fd;
00163     pfd->revents = 0;
00164     pfd->events = POLLOUT | POLLIN; (OUT for transmit, IN for receive)
00165 
00166     (add other sources of I/O here)
00167 
00168     poll(pfd, 1, -1); (or select(); add a timeout if you want)
00169 
00170     if(pfd->revents) {
00171          struct dv1394_status status;
00172 
00173          ioctl(dv1394_fd, DV1394_GET_STATUS, &status);
00174 
00175          if(status.dropped_frames > 0) {
00176               reset_dv1394();
00177          } else {
00178               for(int i = 0; i < status.n_clear_frames; i++) {
00179                   copy_DV_frame();
00180               }
00181          }
00182     }
00183    }
00184 
00185    where copy_DV_frame() reads or writes on the dv1394 file descriptor
00186    (read/write mode) or copies data to/from the mmap ringbuffer and
00187    then calls ioctl(DV1394_SUBMIT_FRAMES) to notify dv1394 that new
00188    frames are availble (mmap mode).
00189 
00190    reset_dv1394() is called in the event of a buffer
00191    underflow/overflow or a halt in the DV stream (e.g. due to a 1394
00192    bus reset). To guarantee recovery from the error, this function
00193    should close the dv1394 file descriptor (and munmap() all
00194    ringbuffer mappings, if you are using them), then re-open the
00195    dv1394 device (and re-map the ringbuffer).
00196 
00197 */
00198 
00199 
00200 /* maximum number of frames in the ringbuffer */
00201 #define DV1394_MAX_FRAMES 32
00202 
00203 /* number of *full* isochronous packets per DV frame */
00204 #define DV1394_NTSC_PACKETS_PER_FRAME 250
00205 #define DV1394_PAL_PACKETS_PER_FRAME  300
00206 
00207 /* size of one frame's worth of DV data, in bytes */
00208 #define DV1394_NTSC_FRAME_SIZE (480 * DV1394_NTSC_PACKETS_PER_FRAME)
00209 #define DV1394_PAL_FRAME_SIZE  (480 * DV1394_PAL_PACKETS_PER_FRAME)
00210 
00211 
00212 /* ioctl() commands */
00213 
00214 enum {
00215         /* I don't like using 0 as a valid ioctl() */
00216         DV1394_INVALID = 0,
00217 
00218 
00219         /* get the driver ready to transmit video.
00220            pass a struct dv1394_init* as the parameter (see below),
00221            or NULL to get default parameters */
00222         DV1394_INIT,
00223 
00224 
00225         /* stop transmitting video and free the ringbuffer */
00226         DV1394_SHUTDOWN,
00227 
00228 
00229         /* submit N new frames to be transmitted, where
00230            the index of the first new frame is first_clear_buffer,
00231            and the index of the last new frame is
00232            (first_clear_buffer + N) % n_frames */
00233         DV1394_SUBMIT_FRAMES,
00234 
00235 
00236         /* block until N buffers are clear (pass N as the parameter)
00237            Because we re-transmit the last frame on underrun, there
00238            will at most be n_frames - 1 clear frames at any time */
00239         DV1394_WAIT_FRAMES,
00240 
00241         /* capture new frames that have been received, where
00242            the index of the first new frame is first_clear_buffer,
00243            and the index of the last new frame is
00244            (first_clear_buffer + N) % n_frames */
00245         DV1394_RECEIVE_FRAMES,
00246 
00247 
00248         DV1394_START_RECEIVE,
00249 
00250 
00251         /* pass a struct dv1394_status* as the parameter (see below) */
00252         DV1394_GET_STATUS,
00253 };
00254 
00255 
00256 
00257 enum pal_or_ntsc {
00258         DV1394_NTSC = 0,
00259         DV1394_PAL
00260 };
00261 
00262 
00263 
00264 
00265 /* this is the argument to DV1394_INIT */
00266 struct dv1394_init {
00267         /* DV1394_API_VERSION */
00268         unsigned int api_version;
00269 
00270         /* isochronous transmission channel to use */
00271         unsigned int channel;
00272 
00273         /* number of frames in the ringbuffer. Must be at least 2
00274            and at most DV1394_MAX_FRAMES. */
00275         unsigned int n_frames;
00276 
00277         /* send/receive PAL or NTSC video format */
00278         enum pal_or_ntsc format;
00279 
00280         /* the following are used only for transmission */
00281 
00282         /* set these to zero unless you want a
00283            non-default empty packet rate (see below) */
00284         unsigned long cip_n;
00285         unsigned long cip_d;
00286 
00287         /* set this to zero unless you want a
00288            non-default SYT cycle offset (default = 3 cycles) */
00289         unsigned int syt_offset;
00290 };
00291 
00292 /* NOTE: you may only allocate the DV frame ringbuffer once each time
00293    you open the dv1394 device. DV1394_INIT will fail if you call it a
00294    second time with different 'n_frames' or 'format' arguments (which
00295    would imply a different size for the ringbuffer). If you need a
00296    different buffer size, simply close and re-open the device, then
00297    initialize it with your new settings. */
00298 
00299 /* Q: What are cip_n and cip_d? */
00300 
00301 /*
00302   A: DV video streams do not utilize 100% of the potential bandwidth offered
00303   by IEEE 1394 (FireWire). To achieve the correct rate of data transmission,
00304   DV devices must periodically insert empty packets into the 1394 data stream.
00305   Typically there is one empty packet per 14-16 data-carrying packets.
00306 
00307   Some DV devices will accept a wide range of empty packet rates, while others
00308   require a precise rate. If the dv1394 driver produces empty packets at
00309   a rate that your device does not accept, you may see ugly patterns on the
00310   DV output, or even no output at all.
00311 
00312   The default empty packet insertion rate seems to work for many people; if
00313   your DV output is stable, you can simply ignore this discussion. However,
00314   we have exposed the empty packet rate as a parameter to support devices that
00315   do not work with the default rate.
00316 
00317   The decision to insert an empty packet is made with a numerator/denominator
00318   algorithm. Empty packets are produced at an average rate of CIP_N / CIP_D.
00319   You can alter the empty packet rate by passing non-zero values for cip_n
00320   and cip_d to the INIT ioctl.
00321 
00322  */
00323 
00324 
00325 
00326 struct dv1394_status {
00327         /* this embedded init struct returns the current dv1394
00328            parameters in use */
00329         struct dv1394_init init;
00330 
00331         /* the ringbuffer frame that is currently being
00332            displayed. (-1 if the device is not transmitting anything) */
00333         int active_frame;
00334 
00335         /* index of the first buffer (ahead of active_frame) that
00336            is ready to be filled with data */
00337         unsigned int first_clear_frame;
00338 
00339         /* how many buffers, including first_clear_buffer, are
00340            ready to be filled with data */
00341         unsigned int n_clear_frames;
00342 
00343         /* how many times the DV stream has underflowed, overflowed,
00344            or otherwise encountered an error, since the previous call
00345            to DV1394_GET_STATUS */
00346         unsigned int dropped_frames;
00347 
00348         /* N.B. The dropped_frames counter is only a lower bound on the actual
00349            number of dropped frames, with the special case that if dropped_frames
00350            is zero, then it is guaranteed that NO frames have been dropped
00351            since the last call to DV1394_GET_STATUS.
00352         */
00353 };
00354 
00355 
00356 #endif /* AVDEVICE_DV1394_H */

Generated on Fri Sep 16 2011 17:17:47 for FFmpeg by  doxygen 1.7.1