Documentation/video4linux/API.html

   1 <HTML><HEAD>
   2 <TITLE>Video4Linux Kernel API Reference v0.1:19990430</TITLE>
   3 </HEAD>
   4 <! Revision History: >
   5 <!   4/30/1999 - Fred Gleason (fredg@wava.com)>
   6 <! Documented extensions for the Radio Data System (RDS) extensions >
   7 <BODY bgcolor="#ffffff">
   8 <H3>Devices</H3>
   9 Video4Linux provides the following sets of device files. These live on the
  10 character device formerly known as "/dev/bttv". /dev/bttv should be a
  11 symlink to /dev/video0 for most people.
  12 <P>
  13 <TABLE>
  14 <TR><TH>Device Name</TH><TH>Minor Range</TH><TH>Function</TH>
  15 <TR><TD>/dev/video</TD><TD>0-63</TD><TD>Video Capture Interface</TD>
  16 <TR><TD>/dev/radio</TD><TD>64-127</TD><TD>AM/FM Radio Devices</TD>
  17 <TR><TD>/dev/vtx</TD><TD>192-223</TD><TD>Teletext Interface Chips</TD>
  18 <TR><TD>/dev/vbi</TD><TD>224-239</TD><TD>Raw VBI Data (Intercast/teletext)</TD>
  19 </TABLE>
  20 <P>
  21 Video4Linux programs open and scan the devices to find what they are looking
  22 for. Capability queries define what each interface supports. The
  23 described API is only defined for video capture cards. The relevant subset
  24 applies to radio cards. Teletext interfaces talk the existing VTX API.
  25 <P>
  26 <H3>Capability Query Ioctl</H3>
  27 The <B>VIDIOCGCAP</B> ioctl call is used to obtain the capability
  28 information for a video device. The <b>struct video_capability</b> object
  29 passed to the ioctl is completed and returned. It contains the following
  30 information
  31 <P>
  32 <TABLE>
  33 <TR><TD><b>name[32]</b><TD>Canonical name for this interface</TD>
  34 <TR><TD><b>type</b><TD>Type of interface</TD>
  35 <TR><TD><b>channels</b><TD>Number of radio/tv channels if appropriate</TD>
  36 <TR><TD><b>audios</b><TD>Number of audio devices if appropriate</TD>
  37 <TR><TD><b>maxwidth</b><TD>Maximum capture width in pixels</TD>
  38 <TR><TD><b>maxheight</b><TD>Maximum capture height in pixels</TD>
  39 <TR><TD><b>minwidth</b><TD>Minimum capture width in pixels</TD>
  40 <TR><TD><b>minheight</b><TD>Minimum capture height in pixels</TD>
  41 </TABLE>
  42 <P>
  43 The type field lists the capability flags for the device. These are
  44 as follows
  45 <P>
  46 <TABLE>
  47 <TR><TH>Name</TH><TH>Description</TH>
  48 <TR><TD><b>VID_TYPE_CAPTURE</b><TD>Can capture to memory</TD>
  49 <TR><TD><b>VID_TYPE_TUNER</b><TD>Has a tuner of some form</TD>
  50 <TR><TD><b>VID_TYPE_TELETEXT</b><TD>Has teletext capability</TD>
  51 <TR><TD><b>VID_TYPE_OVERLAY</b><TD>Can overlay its image onto the frame buffer</TD>
  52 <TR><TD><b>VID_TYPE_CHROMAKEY</b><TD>Overlay is Chromakeyed</TD>
  53 <TR><TD><b>VID_TYPE_CLIPPING</b><TD>Overlay clipping is supported</TD>
  54 <TR><TD><b>VID_TYPE_FRAMERAM</b><TD>Overlay overwrites frame buffer memory</TD>
  55 <TR><TD><b>VID_TYPE_SCALES</b><TD>The hardware supports image scaling</TD>
  56 <TR><TD><b>VID_TYPE_MONOCHROME</b><TD>Image capture is grey scale only</TD>
  57 <TR><TD><b>VID_TYPE_SUBCAPTURE</b><TD>Capture can be of only part of the image</TD>
  58 </TABLE>
  59 <P>
  60 The minimum and maximum sizes listed for a capture device do not imply all
  61 that all height/width ratios or sizes within the range are possible. A
  62 request to set a size will be honoured by the largest available capture
  63 size whose capture is no large than the requested rectangle in either
  64 direction. For example the quickcam has 3 fixed settings.
  65 <P>
  66 <H3>Frame Buffer</H3>
  67 Capture cards that drop data directly onto the frame buffer must be told the
  68 base address of the frame buffer, its size and organisation. This is a
  69 privileged ioctl and one that eventually X itself should set.
  70 <P>
  71 The <b>VIDIOCSFBUF</b> ioctl sets the frame buffer parameters for a capture
  72 card. If the card does not do direct writes to the frame buffer then this
  73 ioctl will be unsupported. The <b>VIDIOCGFBUF</b> ioctl returns the
  74 currently used parameters. The structure used in both cases is a
  75 <b>struct video_buffer</b>.
  76 <P>
  77 <TABLE>
  78 <TR><TD><b>void *base</b></TD><TD>Base physical address of the buffer</TD>
  79 <TR><TD><b>int height</b></TD><TD>Height of the frame buffer</TD>
  80 <TR><TD><b>int width</b></TD><TD>Width of the frame buffer</TD>
  81 <TR><TD><b>int depth</b></TD><TD>Depth of the frame buffer</TD>
  82 <TR><TD><b>int bytesperline</b></TD><TD>Number of bytes of memory between the start of two adjacent lines</TD>
  83 </TABLE>
  84 <P>
  85 Note that these values reflect the physical layout of the frame buffer.
  86 The visible area may be smaller. In fact under XFree86 this is commonly the
  87 case. XFree86 DGA can provide the parameters required to set up this ioctl.
  88 Setting the base address to NULL indicates there is no physical frame buffer
  89 access.
  90 <P>
  91 <H3>Capture Windows</H3>
  92 The capture area is described by a <b>struct video_window</b>. This defines
  93 a capture area and the clipping information if relevant. The
  94 <b>VIDIOCGWIN</b> ioctl recovers the current settings and the
  95 <b>VIDIOCSWIN</b> sets new values. A successful call to <b>VIDIOCSWIN</b>
  96 indicates that a suitable set of parameters have been chosen. They do not
  97 indicate that exactly what was requested was granted. The program should
  98 call <b>VIDIOCGWIN</b> to check if the nearest match was suitable. The
  99 <b>struct video_window</b> contains the following fields.
 100 <P>
 101 <TABLE>
 102 <TR><TD><b>x</b><TD>The X co-ordinate specified in X windows format.</TD>
 103 <TR><TD><b>y</b><TD>The Y co-ordinate specified in X windows format.</TD>
 104 <TR><TD><b>width</b><TD>The width of the image capture.</TD>
 105 <TR><TD><b>height</b><TD>The height of the image capture.</TD>
 106 <TR><TD><b>chromakey</b><TD>A host order RGB32 value for the chroma key.</TD>
 107 <TR><TD><b>flags</b><TD>Additional capture flags.</TD>
 108 <TR><TD><b>clips</b><TD>A list of clipping rectangles. <em>(Set only)</em></TD>
 109 <TR><TD><b>clipcount</b><TD>The number of clipping rectangles. <em>(Set only)</em></TD>
 110 </TABLE>
 111 <P>
 112 Clipping rectangles are passed as an array. Each clip consists of the following
 113 fields available to the user.
 114 <P>
 115 <TABLE>
 116 <TR><TD><b>x</b></TD><TD>X co-ordinate of rectangle to skip</TD>
 117 <TR><TD><b>y</b></TD><TD>Y co-ordinate of rectangle to skip</TD>
 118 <TR><TD><b>width</b></TD><TD>Width of rectangle to skip</TD>
 119 <TR><TD><b>height</b></TD><TD>Height of rectangle to skip</TD>
 120 </TABLE>
 121 <P>
 122 Merely setting the window does not enable capturing. Overlay capturing
 123 (i.e. PCI-PCI transfer to the frame buffer of the video card)
 124 is activated by passing the <b>VIDIOCCAPTURE</b> ioctl a value of 1, and
 125 disabled by passing it a value of 0.
 126 <P>
 127 Some capture devices can capture a subfield of the image they actually see.
 128 This is indicated when VIDEO_TYPE_SUBCAPTURE is defined.
 129 The video_capture describes the time and special subfields to capture.
 130 The video_capture structure contains the following fields.
 131 <P>
 132 <TABLE>
 133 <TR><TD><b>x</b></TD><TD>X co-ordinate of source rectangle to grab</TD>
 134 <TR><TD><b>y</b></TD><TD>Y co-ordinate of source rectangle to grab</TD>
 135 <TR><TD><b>width</b></TD><TD>Width of source rectangle to grab</TD>
 136 <TR><TD><b>height</b></TD><TD>Height of source rectangle to grab</TD>
 137 <TR><TD><b>decimation</b></TD><TD>Decimation to apply</TD>
 138 <TR><TD><b>flags</b></TD><TD>Flag settings for grabbing</TD>
 139 </TABLE>
 140 The available flags are
 141 <P>
 142 <TABLE>
 143 <TR><TH>Name</TH><TH>Description</TH>
 144 <TR><TD><b>VIDEO_CAPTURE_ODD</b><TD>Capture only odd frames</TD>
 145 <TR><TD><b>VIDEO_CAPTURE_EVEN</b><TD>Capture only even frames</TD>
 146 </TABLE>
 147 <P>
 148 <H3>Video Sources</H3>
 149 Each video4linux video or audio device captures from one or more
 150 source <b>channels</b>. Each channel can be queries with the
 151 <b>VDIOCGCHAN</b> ioctl call. Before invoking this function the caller
 152 must set the channel field to the channel that is being queried. On return
 153 the <b>struct video_channel</b> is filled in with information about the
 154 nature of the channel itself.
 155 <P>
 156 The <b>VIDIOCSCHAN</b> ioctl takes an integer argument and switches the
 157 capture to this input. It is not defined whether parameters such as colour
 158 settings or tuning are maintained across a channel switch. The caller should
 159 maintain settings as desired for each channel. (This is reasonable as
 160 different video inputs may have different properties).
 161 <P>
 162 The <b>struct video_channel</b> consists of the following
 163 <P>
 164 <TABLE>
 165 <TR><TD><b>channel</b></TD><TD>The channel number</TD>
 166 <TR><TD><b>name</b></TD><TD>The input name - preferably reflecting the label
 167 on the card input itself</TD>
 168 <TR><TD><b>tuners</b></TD><TD>Number of tuners for this input</TD>
 169 <TR><TD><b>flags</b></TD><TD>Properties the tuner has</TD>
 170 <TR><TD><b>type</b></TD><TD>Input type (if known)</TD>
 171 <TR><TD><b>norm</b><TD>The norm for this channel</TD>
 172 </TABLE>
 173 <P>
 174 The flags defined are
 175 <P>
 176 <TABLE>
 177 <TR><TD><b>VIDEO_VC_TUNER</b><TD>Channel has tuners.</TD>
 178 <TR><TD><b>VIDEO_VC_AUDIO</b><TD>Channel has audio.</TD>
 179 <TR><TD><b>VIDEO_VC_NORM</b><TD>Channel has norm setting.</TD>
 180 </TABLE>
 181 <P>
 182 The types defined are
 183 <P>
 184 <TABLE>
 185 <TR><TD><b>VIDEO_TYPE_TV</b><TD>The input is a TV input.</TD>
 186 <TR><TD><b>VIDEO_TYPE_CAMERA</b><TD>The input is a camera.</TD>
 187 </TABLE>
 188 <P>
 189 <H3>Image Properties</H3>
 190 The image properties of the picture can be queried with the <b>VIDIOCGPICT</b>
 191 ioctl which fills in a <b>struct video_picture</b>. The <b>VIDIOCSPICT</b>
 192 ioctl allows values to be changed. All values except for the palette type
 193 are scaled between 0-65535.
 194 <P>
 195 The <b>struct video_picture</b> consists of the following fields
 196 <P>
 197 <TABLE>
 198 <TR><TD><b>brightness</b><TD>Picture brightness</TD>
 199 <TR><TD><b>hue</b><TD>Picture hue (colour only)</TD>
 200 <TR><TD><b>colour</b><TD>Picture colour (colour only)</TD>
 201 <TR><TD><b>contrast</b><TD>Picture contrast</TD>
 202 <TR><TD><b>whiteness</b><TD>The whiteness (greyscale only)</TD>
 203 <TR><TD><b>depth</b><TD>The capture depth (may need to match the frame buffer depth)</TD>
 204 <TR><TD><b>palette</b><TD>Reports the palette that should be used for this image</TD>
 205 </TABLE>
 206 <P>
 207 The following palettes are defined
 208 <P>
 209 <TABLE>
 210 <TR><TD><b>VIDEO_PALETTE_GREY</b><TD>Linear intensity grey scale (255 is brightest).</TD>
 211 <TR><TD><b>VIDEO_PALETTE_HI240</b><TD>The BT848 8bit colour cube.</TD>
 212 <TR><TD><b>VIDEO_PALETTE_RGB565</b><TD>RGB565 packed into 16 bit words.</TD>
 213 <TR><TD><b>VIDEO_PALETTE_RGB555</b><TD>RGV555 packed into 16 bit words, top bit undefined.</TD>
 214 <TR><TD><b>VIDEO_PALETTE_RGB24</b><TD>RGB888 packed into 24bit words.</TD>
 215 <TR><TD><b>VIDEO_PALETTE_RGB32</b><TD>RGB888 packed into the low 3 bytes of 32bit words. The top 8bits are undefined.</TD>
 216 <TR><TD><b>VIDEO_PALETTE_YUV422</b><TD>Video style YUV422 - 8bits packed 4bits Y 2bits U 2bits V</TD>
 217 <TR><TD><b>VIDEO_PALETTE_YUYV</b><TD>Describe me</TD>
 218 <TR><TD><b>VIDEO_PALETTE_UYVY</b><TD>Describe me</TD>
 219 <TR><TD><b>VIDEO_PALETTE_YUV420</b><TD>YUV420 capture</TD>
 220 <TR><TD><b>VIDEO_PALETTE_YUV411</b><TD>YUV411 capture</TD>
 221 <TR><TD><b>VIDEO_PALETTE_RAW</b><TD>RAW capture (BT848)</TD>
 222 <TR><TD><b>VIDEO_PALETTE_YUV422P</b><TD>YUV 4:2:2 Planar</TD>
 223 <TR><TD><b>VIDEO_PALETTE_YUV411P</b><TD>YUV 4:1:1 Planar</TD>
 224 </TABLE>
 225 <P>
 226 <H3>Tuning</H3>
 227 Each video input channel can have one or more tuners associated with it. Many
 228 devices will not have tuners. TV cards and radio cards will have one or more
 229 tuners attached.
 230 <P>
 231 Tuners are described by a <b>struct video_tuner</b> which can be obtained by
 232 the <b>VIDIOCGTUNER</b> ioctl. Fill in the tuner number in the structure
 233 then pass the structure to the ioctl to have the data filled in. The
 234 tuner can be switched using <b>VIDIOCSTUNER</b> which takes an integer argument
 235 giving the tuner to use. A struct tuner has the following fields
 236 <P>
 237 <TABLE>
 238 <TR><TD><b>tuner</b><TD>Number of the tuner</TD>
 239 <TR><TD><b>name</b><TD>Canonical name for this tuner (eg FM/AM/TV)</TD>
 240 <TR><TD><b>rangelow</b><TD>Lowest tunable frequency</TD>
 241 <TR><TD><b>rangehigh</b><TD>Highest tunable frequency</TD>
 242 <TR><TD><b>flags</b><TD>Flags describing the tuner</TD>
 243 <TR><TD><b>mode</b><TD>The video signal mode if relevant</TD>
 244 <TR><TD><b>signal</b><TD>Signal strength if known - between 0-65535</TD>
 245 </TABLE>
 246 <P>
 247 The following flags exist
 248 <P>
 249 <TABLE>
 250 <TR><TD><b>VIDEO_TUNER_PAL</b><TD>PAL tuning is supported</TD>
 251 <TR><TD><b>VIDEO_TUNER_NTSC</b><TD>NTSC tuning is supported</TD>
 252 <TR><TD><b>VIDEO_TUNER_SECAM</b><TD>SECAM tuning is supported</TD>
 253 <TR><TD><b>VIDEO_TUNER_LOW</b><TD>Frequency is in a lower range</TD>
 254 <TR><TD><b>VIDEO_TUNER_NORM</b><TD>The norm for this tuner is settable</TD>
 255 <TR><TD><b>VIDEO_TUNER_STEREO_ON</b><TD>The tuner is seeing stereo audio</TD>
 256 <TR><TD><b>VIDEO_TUNER_RDS_ON</b><TD>The tuner is seeing a RDS datastream</TD>
 257 <TR><TD><b>VIDEO_TUNER_MBS_ON</b><TD>The tuner is seeing a MBS datastream</TD>
 258 </TABLE>
 259 <P>
 260 The following modes are defined
 261 <P>
 262 <TABLE>
 263 <TR><TD><b>VIDEO_MODE_PAL</b><TD>The tuner is in PAL mode</TD>
 264 <TR><TD><b>VIDEO_MODE_NTSC</b><TD>The tuner is in NTSC mode</TD>
 265 <TR><TD><b>VIDEO_MODE_SECAM</b><TD>The tuner is in SECAM mode</TD>
 266 <TR><TD><b>VIDEO_MODE_AUTO</b><TD>The tuner auto switches, or mode does not apply</TD>
 267 </TABLE>
 268 <P>
 269 Tuning frequencies are an unsigned 32bit value in 1/16th MHz or if the
 270 <b>VIDEO_TUNER_LOW</b> flag is set they are in 1/16th KHz. The current
 271 frequency is obtained as an unsigned long via the <b>VIDIOCGFREQ</b> ioctl and
 272 set by the <b>VIDIOCSFREQ</b> ioctl.
 273 <P>
 274 <H3>Audio</H3>
 275 TV and Radio devices have one or more audio inputs that may be selected.
 276 The audio properties are queried by passing a <b>struct video_audio</b> to <b>VIDIOCGAUDIO</b> ioctl. The
 277 <b>VIDIOCSAUDIO</b> ioctl sets audio properties.
 278 <P>
 279 The structure contains the following fields
 280 <P>
 281 <TABLE>
 282 <TR><TD><b>audio</b><TD>The channel number</TD>
 283 <TR><TD><b>volume</b><TD>The volume level</TD>
 284 <TR><TD><b>bass</b><TD>The bass level</TD>
 285 <TR><TD><b>treble</b><TD>The treble level</TD>
 286 <TR><TD><b>flags</b><TD>Flags describing the audio channel</TD>
 287 <TR><TD><b>name</b><TD>Canonical name for the audio input</TD>
 288 <TR><TD><b>mode</b><TD>The mode the audio input is in</TD>
 289 <TR><TD><b>balance</b><TD>The left/right balance</TD>
 290 <TR><TD><b>step</b><TD>Actual step used by the hardware</TD>
 291 </TABLE>
 292 <P>
 293 The following flags are defined
 294 <P>
 295 <TABLE>
 296 <TR><TD><b>VIDEO_AUDIO_MUTE</b><TD>The audio is muted</TD>
 297 <TR><TD><b>VIDEO_AUDIO_MUTABLE</b><TD>Audio muting is supported</TD>
 298 <TR><TD><b>VIDEO_AUDIO_VOLUME</b><TD>The volume is controllable</TD>
 299 <TR><TD><b>VIDEO_AUDIO_BASS</b><TD>The bass is controllable</TD>
 300 <TR><TD><b>VIDEO_AUDIO_TREBLE</b><TD>The treble is controllable</TD>
 301 <TR><TD><b>VIDEO_AUDIO_BALANCE</b><TD>The balance is controllable</TD>
 302 </TABLE>
 303 <P>
 304 The following decoding modes are defined
 305 <P>
 306 <TABLE>
 307 <TR><TD><b>VIDEO_SOUND_MONO</b><TD>Mono signal</TD>
 308 <TR><TD><b>VIDEO_SOUND_STEREO</b><TD>Stereo signal (NICAM for TV)</TD>
 309 <TR><TD><b>VIDEO_SOUND_LANG1</b><TD>European TV alternate language 1</TD>
 310 <TR><TD><b>VIDEO_SOUND_LANG2</b><TD>European TV alternate language 2</TD>
 311 </TABLE>
 312 <P>
 313 <H3>Reading Images</H3>
 314 Each call to the <b>read</b> syscall returns the next available image
 315 from the device. It is up to the caller to set format and size (using
 316 the VIDIOCSPICT and VIDIOCSWIN ioctls) and then to pass a suitable
 317 size buffer and length to the function. Not all devices will support
 318 read operations.
 319 <P>
 320 A second way to handle image capture is via the mmap interface if supported.
 321 To use the mmap interface a user first sets the desired image size and depth
 322 properties. Next the VIDIOCGMBUF ioctl is issued. This reports the size
 323 of buffer to mmap and the offset within the buffer for each frame. The
 324 number of frames supported is device dependent and may only be one.
 325 <P>
 326 The video_mbuf structure contains the following fields
 327 <P>
 328 <TABLE>
 329 <TR><TD><b>size</b><TD>The number of bytes to map</TD>
 330 <TR><TD><b>frames</b><TD>The number of frames</TD>
 331 <TR><TD><b>offsets</b><TD>The offset of each frame</TD>
 332 </TABLE>
 333 <P>
 334 Once the mmap has been made the VIDIOCMCAPTURE ioctl starts the
 335 capture to a frame using the format and image size specified in the
 336 video_mmap (which should match or be below the initial query size).
 337 When the VIDIOCMCAPTURE ioctl returns the frame is <em>not</em>
 338 captured yet, the driver just instructed the hardware to start the
 339 capture.  The application has to use the VIDIOCSYNC ioctl to wait
 340 until the capture of a frame is finished.  VIDIOCSYNC takes the frame
 341 number you want to wait for as argument.
 342 <p>
 343 It is allowed to call VIDIOCMCAPTURE multiple times (with different
 344 frame numbers in video_mmap->frame of course) and thus have multiple
 345 outstanding capture requests.  A simple way do to double-buffering
 346 using this feature looks like this:
 347 <pre>
 348 /* setup everything */
 349 VIDIOCMCAPTURE(0)
 350 while (whatever) {
 351    VIDIOCMCAPTURE(1)
 352    VIDIOCSYNC(0)
 353    /* process frame 0 while the hardware captures frame 1 */
 354    VIDIOCMCAPTURE(0)
 355    VIDIOCSYNC(1)
 356    /* process frame 1 while the hardware captures frame 0 */
 357 }
 358 </pre>
 359 Note that you are <em>not</em> limited to only two frames.  The API
 360 allows up to 32 frames, the VIDIOCGMBUF ioctl returns the number of
 361 frames the driver granted.  Thus it is possible to build deeper queues
 362 to avoid loosing frames on load peaks.
 363 <p>
 364 While capturing to memory the driver will make a "best effort" attempt
 365 to capture to screen as well if requested. This normally means all
 366 frames that "miss" memory mapped capture will go to the display.
 367 <P>
 368 A final ioctl exists to allow a device to obtain related devices if a
 369 driver has multiple components (for example video0 may not be associated
 370 with vbi0 which would cause an intercast display program to make a bad
 371 mistake). The VIDIOCGUNIT ioctl reports the unit numbers of the associated
 372 devices if any exist. The video_unit structure has the following fields.
 373 <P>
 374 <TABLE>
 375 <TR><TD><b>video</b><TD>Video capture device</TD>
 376 <TR><TD><b>vbi</b><TD>VBI capture device</TD>
 377 <TR><TD><b>radio</b><TD>Radio device</TD>
 378 <TR><TD><b>audio</b><TD>Audio mixer</TD>
 379 <TR><TD><b>teletext</b><TD>Teletext device</TD>
 380 </TABLE>
 381 <P>
 382 <H3>RDS Datastreams</H3>
 383 For radio devices that support it, it is possible to receive Radio Data
 384 System (RDS) data by means of a read() on the device.  The data is packed in
 385 groups of three, as follows:
 386 <TABLE>
 387 <TR><TD>First Octet</TD><TD>Least Significant Byte of RDS Block</TD></TR>
 388 <TR><TD>Second Octet</TD><TD>Most Significant Byte of RDS Block
 389 <TR><TD>Third Octet</TD><TD>Bit 7:</TD><TD>Error bit.  Indicates that
 390 an uncorrectable error occurred during reception of this block.</TD></TR>
 391 <TR><TD>&nbsp;</TD><TD>Bit 6:</TD><TD>Corrected bit.  Indicates that
 392 an error was corrected for this data block.</TD></TR>
 393 <TR><TD>&nbsp;</TD><TD>Bits 5-3:</TD><TD>Received Offset.  Indicates the
 394 offset received by the sync system.</TD></TR>
 395 <TR><TD>&nbsp;</TD><TD>Bits 2-0:</TD><TD>Offset Name.  Indicates the
 396 offset applied to this data.</TD></TR>
 397 </TABLE>
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