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
timings <pixclock> <left> <right> <upper> <lower> <hslen> <vslen>
options <value>
OPTIONS
geometry options:
timing options:
other options:
- 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 provided 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 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
INTERNALS
Generally a frame buffer display is organized as follows:
+---+---------------+---+---+
| | ^ | | |
| | | 5 | | |
| | v | | |
+---#################---+---+
| # ^ # | |
| # | # | |
| # | # | |
| 1 # |2 #
3 | 4 |
|<->#<------+------>#<->|<->|
| # | # | |
| # | 6 # | |
| # | # | |
| # v # | |
+---#################---+---+
| | ^ | | |
| | | 7 | | |
| | v | | |
+---+---------------+---+---+
| | ^ | | |
| | | 8 | | |
| | v | | |
+---+---------------+---+---+
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
line = pixclock * htotal
hfreq = 1E12 / line = 1E12 / (pixclock * htotal)
if (lace) vtotal /= 2
if (double) vtotal *= 2
frame = vtotal * line
vfreq = 1E12 / frame = hfreq / vtotal
SEE ALSO
Aug 1996 | local |