fb.modes - frame buffer modes file


   /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>
          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 length/offset)

          green  green color bitfields (in length or length/offset)

          blue   blue color bitfields (in length or length/offset)

          alpha  alpha color bitfields (in length or length/offset)

   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

          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  provided  externally  instead.  Note  that  this
                 option may not be supported by every frame buffer device

          sync <number>
                 custom sync flags (frame buffer driver dependent)

          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 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 colors


   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
   doublescan 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


   fbset(8), fbdev(4)


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