File: fb.modes.5

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.TH fb.modes 8 "Aug 1996" local "Linux frame buffer utils"
.SH NAME
fb.modes \- frame buffer modes file
.SH DESCRIPTION
.I /etc/fb.modes
contains an unlimited number of video mode descriptions. The general format
of a video mode is:
.sp
mode
.RI \" name \"
.RS
geometry
.RI < xres >
.RI < yres >
.RI < vxres >
.RI < vyres >
.RI < depth >
.br
timings
.RI < pixclock >
.RI < left >
.RI < right >
.RI < upper >
.RI < lower >
.RI < hslen >
.RI < vslen >
.br
.B options
.RI < value >
.RE
endmode
.SH OPTIONS
geometry options:
.RS
.TP
.I xres
visible horizontal resolution (in pixels)
.TP
.I yres
visible vertical resolution (in pixels)
.TP
.I vxres
virtual horizontal resolution (in pixels)
.TP
.I vyres
virtual vertical resolution (in pixels)
.TP
.I depth
display depth (in bits per pixel)
.RE
.PP
timing options:
.RS
.TP
.I pixclock
length of one pixel (in picoseconds)
.TP
.I left
left margin (in pixels)
.TP
.I right
right margin (in pixels)
.TP
.I upper
upper margin (in pixel lines)
.TP
.I lower
lower margin (in pixel lines)
.TP
.I hslen
horizontal sync length (in pixels)
.TP
.I vslen
vertical sync length (in pixel lines)
.RE
.PP
other options:
.RS
the first value of this options is the default
.TP
.IR \fBhsync "\ {" low | high }
the horizontal sync polarity
.TP
.IR \fBvsync "\ {" low | high }
the vertical sync polarity
.TP
.IR \fBcsync "\ {" low | high }
the composite sync polarity
.TP
.IR \fBextsync "\ {" 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
.TP
.IR \fBlaced "\ {" 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
.TP
.IR \fBdouble "\ {" 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
.RE
.SH INTERNALS
Generally a frame buffer display is organized as follows:
.sp
.ad c
+\-\-\-+\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-+\-\-\-+\-\-\-+
.br
.RB "|\ \ \ |\ \ \ \ \ \ \ " ^ "\ \ \ \ \ \ \ |\ \ \ |\ \ \ |"
.br
.RB "|\ \ \ |\ \ \ \ \ \ \ " | "\ " \fI5 "\ \ \ \ \ |\ \ \ |\ \ \ |"
.br
.RB "|\ \ \ |\ \ \ \ \ \ \ " v "\ \ \ \ \ \ \ |\ \ \ |\ \ \ |"
.br
+\-\-\-#################\-\-\-+\-\-\-+
.br
.RB "|\ \ \ #\ \ \ \ \ \ \ " ^ "\ \ \ \ \ \ \ #\ \ \ |\ \ \ |"
.br
.RB "|\ \ \ #\ \ \ \ \ \ \ " | "\ \ \ \ \ \ \ #\ \ \ |\ \ \ |"
.br
.RB "|\ \ \ #\ \ \ \ \ \ \ " | "\ \ \ \ \ \ \ #\ \ \ |\ \ \ |"
.br
.RI "| " 1 " #       " \fB| "   " 2 "   # " 3 " | " 4 " |"
.br
.RB "|" "<\->" "#" "<\-\-\-\-\-\-+\-\-\-\-\-\->" "#" "<\->" "|" "<\->" "|"
.br
.RB "|\ \ \ #\ \ \ \ \ \ \ " | "\ \ \ \ \ \ \ #\ \ \ |\ \ \ |"
.br
.RB "|\ \ \ #\ \ \ \ \ \ \ " | "\ " \fI6 "\ \ \ \ \ #\ \ \ |\ \ \ |"
.br
.RB "|\ \ \ #\ \ \ \ \ \ \ " | "\ \ \ \ \ \ \ #\ \ \ |\ \ \ |"
.br
.RB "|\ \ \ #\ \ \ \ \ \ \ " v "\ \ \ \ \ \ \ #\ \ \ |\ \ \ |"
.br
+\-\-\-#################\-\-\-+\-\-\-+
.br
.RB "|\ \ \ |\ \ \ \ \ \ \ " ^ "\ \ \ \ \ \ \ |\ \ \ |\ \ \ |"
.br
.RB "|\ \ \ |\ \ \ \ \ \ \ " | "\ " \fI7 "\ \ \ \ \ |\ \ \ |\ \ \ |"
.br
.RB "|\ \ \ |\ \ \ \ \ \ \ " v "\ \ \ \ \ \ \ |\ \ \ |\ \ \ |"
.br
+\-\-\-+\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-+\-\-\-+\-\-\-+
.br
.RB "|\ \ \ |\ \ \ \ \ \ \ " ^ "\ \ \ \ \ \ \ |\ \ \ |\ \ \ |"
.br
.RB "|\ \ \ |\ \ \ \ \ \ \ " | "\ " \fI8 "\ \ \ \ \ |\ \ \ |\ \ \ |"
.br
.RB "|\ \ \ |\ \ \ \ \ \ \ " v "\ \ \ \ \ \ \ |\ \ \ |\ \ \ |"
.br
+\-\-\-+\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-+\-\-\-+\-\-\-+
.sp
.ad n
.RS
.I 1
\t left margin
.br
.I 2
\t xres
.br
.I 3
\t right margin
.br
.I 4
\t horizontal sync len
.br
.I 5
\t upper margin
.br
.I 6
\t yres
.br
.I 7
\t lower margin
.br
.I 8
\t vertical sync len
.RE
.sp
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
.RS
.sp
htotal\ =\ left\ +\ xres\ +\ right\ +\ hslen
.br
vtotal\ =\ upper\ +\ yres\ +\ lower\ +\ vslen
.sp
.RE
The length of one line can now be calculated with pixclock
.RS
.sp
line\ =\ pixclock\ *\ htotal
.sp
.RE
and we have the horizontal frequency
.RS
.sp
hfreq\ =\ 1E12\ /\ line\ =\ 1E12\ /\ (pixclock\ *\ htotal)
.sp
.RE
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
.RS
.sp
if\ (lace)\ \ \ vtotal\ /=\ 2
.br
if\ (double)\ vtotal\ *=\ 2
.sp
frame\ =\ vtotal\ *\ line
.sp
.RE
and we get also the vertical frequency
.RS
.sp
vfreq\ =\ 1E12\ /\ frame\ =\ hfreq\ /\ vtotal
.sp
.RE
.SH SEE ALSO
.BR fbset "(8), " fbdev (4)