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:
+---+---------------+---+---+
+---#################---+---+
| 1 # \fB| 2 # 3 | 4 |
+---#################---+---+
+---+---------------+---+---+
+---+---------------+---+---+
1 t left margin
2 t xres
3 t right margin
4 t horizontal sync len
5 t upper margin
6 t yres
7 t lower margin
8 t 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
