fb.modes(5)                                                  Linux frame buffer utils                                                  fb.modes(5)

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>
              rgba <red,green,blue,alpha>
       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)

       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  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

              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

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)

2.1                                                                 2003-08-07                                                         fb.modes(5)