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fb.modes - frame buffer modes file

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 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

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 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
 

SEE ALSO

fbset(8), fbdev(4)
2003-08-07 2.1