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