fb.modes(8)						     Linux frame buffer utils						       fb.modes(8)

NAME

       fb.modes - frame buffer modes file

DESCRIPTION

       /etc/fb.modes contains an unlimited number of video mode descriptions. The general format of a video mode is:

       mode
	      geometry <xres> <yres> <vxres> <vyres> <depth>
	      timings <pixclock> <left> <right> <upper> <lower> <hslen> <vslen>
	      options <value>
       endmode

OPTIONS

       geometry options:

	      xres   visible horizontal resolution (in pixels)

	      yres   visible vertical resolution (in pixels)

	      vxres  virtual horizontal resolution (in pixels)

	      vyres  virtual vertical resolution (in pixels)

	      depth  display depth (in bits per pixel)

       timing options:

	      pixclock
		     length of one pixel (in picoseconds)

	      left   left margin (in pixels)

	      right  right margin (in pixels)

	      upper  upper margin (in pixel lines)

	      lower  lower margin (in pixel lines)

	      hslen  horizontal sync length (in pixels)

	      vslen  vertical sync length (in pixel lines)

       other options:
	      the first value of this options is the default

	      hsync {low|high}
		     the horizontal sync polarity

	      vsync {low|high}
		     the vertical sync polarity

	      csync {low|high}
		     the composite sync polarity

	      extsync {false|true}
		     enable  or disable external resync. If enabled the sync timings are not generated by the frame buffer device and must be pro-
		     vided externally instead. Note that this option may not be supported by every frame buffer device

	      laced {false|true}
		     enable or disable interlace. If enabled the display will be split in two frames, each frame contains only even and odd  lines
		     respectively. These two frames will be displayed alternating, this way twice the lines can be displayed and the vertical fre-
		     quency for monitor stays the same, but the visible vertical frequency gets halved

	      double {false|true}
		     enable or disable doublescan. If enabled every line will be displayed twice and this way the horizontal frequency can  easily
		     be  doubled,  so that the same resolution can be displayed on different monitors, even if the horizontal frequency specifica-
		     tion differs. Note that this option may not be supported by every frame buffer device

INTERNALS

       Generally a frame buffer display is organized as follows:

							      +---+---------------+---+---+
							      |   |	  ^	  |   |   |
							      |   |	  | 5	  |   |   |
							      |   |	  v	  |   |   |
							      +---#################---+---+
							      |   #	  ^	  #   |   |
							      |   #	  |	  #   |   |
							      |   #	  |	  #   |   |
							      | 1 #	  |   2   # 3 | 4 |
							      |<->#<------+------>#<->|<->|
							      |   #	  |	  #   |   |
							      |   #	  | 6	  #   |   |
							      |   #	  |	  #   |   |
							      |   #	  v	  #   |   |
							      +---#################---+---+
							      |   |	  ^	  |   |   |
							      |   |	  | 7	  |   |   |
							      |   |	  v	  |   |   |
							      +---+---------------+---+---+
							      |   |	  ^	  |   |   |
							      |   |	  | 8	  |   |   |
							      |   |	  v	  |   |   |
							      +---+---------------+---+---+

	      1  left margin
	      2  xres
	      3  right margin
	      4  horizontal sync len
	      5  upper margin
	      6  yres
	      7  lower margin
	      8  vertical sync len

       The area bordered with `#' is the visible display area. Horizontal and vertical frequencies can now easily be calculated, for this the  sum
       of horizontal or vertical values are important

	      htotal = left + xres + right + hslen
	      vtotal = upper + yres + lower + vslen

       The length of one line can now be calculated with pixclock

	      line = pixclock * htotal

       and we have the horizontal frequency

	      hfreq = 1E12 / line = 1E12 / (pixclock * htotal)

       To  get	the vertical frequency vtotal must eventually adjusted. If the display is laced, vtotal must be halved or if the display is a dou-
       blescan one, vtotal must be doubled. Now we can calculate the length of one frame

	      if (lace)   vtotal /= 2
	      if (double) vtotal *= 2

	      frame = vtotal * line

       and we get also the vertical frequency

	      vfreq = 1E12 / frame = hfreq / vtotal

SEE ALSO

       fbset(8), fbdev(4)

local								     Aug 1996							       fb.modes(8)