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

              geometry <xres> <yres> <vxres> <vyres> <depth>
              timings <pixclock> <left> <right>  <upper>  <lower>
              <hslen> <vslen>
              options <value>
              rgba <red,green,blue,alpha>


       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:

                     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)

       rgba options (only valid with truecolor):

              red    red    color   bitfields   (in   length   or

              green  green  color   bitfields   (in   length   or

              blue   blue   color   bitfields   (in   length   or
                     the composite sync polarity

              gsync {low|high}
                     the sync on green polarity

              bcast {false|true}
                     enable   or   disable  broadcast  modes.  If
                     enabled the frame buffer generates the exact
                     timings  fot  several  broadcast modes (e.g.
                     PAL or NTSC). Note that this option may  not
                     be supported by every frame buffer

              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 dis­
                     played alternating, this way twice the lines
                     can  be displayed and the vertical frequency
                     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 specification  differs.
                     Note  that  this option may not be supported
                     by every frame buffer device

              nostd <number>
                     select nonstandard video mode

              accel {false|true}
                     enable or disable hardware text acceleration

              grayscale {false|true}
                     enable or disable graylevels instead of col­


       Generally a frame buffer display is organized as follows:
                     |   #       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 cal­
       culated, 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 doublescan one, vtotal must be dou­
       bled. 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



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