fb.modes - Online Linux Manual PageSection : 5
Updated : 2003-08-07
Source : 2.1
Note : Linux frame buffer utils
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 .RI geometry <xres> <yres> <vxres> <vyres> <depth>
timings <pixclock> <left> <right> <upper> <lower> <hslen> <vslen>
options <value>
rgba <red,green,blue,alpha>
endmode

OPTIONSgeometry 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

INTERNALSGenerally a frame buffer display is organized as follows: +−−−+−−−−−−−−−−−−−−−+−−−+−−−+
|   |       ^       |   |   |
|   |       | 5     |   |   |
|   |       v       |   |   |
+−−−#################−−−+−−−+
|   #       ^       #   |   |
|   #       |       #   |   |
|   #       |       #   |   |
| 1 # | 2 # 3 | 4 |
|<>#<−−−−−−+−−−−−−>#<>|<>|
|   #       |       #   |   |
|   #       | 6     #   |   |
|   #       |       #   |   |
|   #       v       #   |   |
+−−−#################−−−+−−−+
|   |       ^       |   |   |
|   |       | 7     |   |   |
|   |       v       |   |   |
+−−−+−−−−−−−−−−−−−−−+−−−+−−−+
|   |       ^       |   |   |
|   |       | 8     |   |   |
|   |       v       |   |   |
+−−−+−−−−−−−−−−−−−−−+−−−+−−−+ .ad n 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 ALSOfbset(8),"fbdev(4)

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