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split single line into two line or three lines
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fb.modes(8) Linux frame buffer utils fb.modes(8) 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> 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) 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 extsync {false|true} enable or disable external resync. If enabled the sync timings are not generated by the frame buffer device and must be pro- vided 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 fre- quency 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 specifica- tion differs. Note that this option may not be supported by every frame buffer device 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 dou- blescan 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) local Aug 1996 fb.modes(8)
