fb.modes(8) Linux frame buffer utils fb.modes(8)NAMEfb.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 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 dis‐
played alternating, this way twice the lines can be dis‐
played 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
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 doubles‐
can 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 ALSOfbset(8), fbdev(4)local Aug 1996 fb.modes(8)
