1fb.modes(8) Linux frame buffer utils fb.modes(8)
2
6 fb.modes - frame buffer modes file
7
9 /etc/fb.modes contains an unlimited number of video mode descriptions.
10 The general format of a video mode is:
11 mode
13 geometry <xres> <yres> <vxres> <vyres> <depth>
14 timings <pixclock> <left> <right> <upper> <lower> <hslen>
15 <vslen>
16 options <value>
17 endmode
18
20 geometry options:
21 xres visible horizontal resolution (in pixels)
23 yres visible vertical resolution (in pixels)
25 vxres virtual horizontal resolution (in pixels)
27 vyres virtual vertical resolution (in pixels)
29 depth display depth (in bits per pixel)
31 timing options:
33 pixclock
35 length of one pixel (in picoseconds)
36 left left margin (in pixels)
38 right right margin (in pixels)
40 upper upper margin (in pixel lines)
42 lower lower margin (in pixel lines)
44 hslen horizontal sync length (in pixels)
46 vslen vertical sync length (in pixel lines)
48 other options:
50 the first value of this options is the default
51 hsync {low|high}
53 the horizontal sync polarity
54 vsync {low|high}
56 the vertical sync polarity
57 csync {low|high}
59 the composite sync polarity
60 extsync {false|true}
62 enable or disable external resync. If enabled the sync
63 timings are not generated by the frame buffer device and
64 must be provided externally instead. Note that this
65 option may not be supported by every frame buffer device
66 laced {false|true}
68 enable or disable interlace. If enabled the display will
69 be split in two frames, each frame contains only even and
70 odd lines respectively. These two frames will be dis‐
71 played alternating, this way twice the lines can be dis‐
72 played and the vertical frequency for monitor stays the
73 same, but the visible vertical frequency gets halved
74 double {false|true}
76 enable or disable doublescan. If enabled every line will
77 be displayed twice and this way the horizontal frequency
78 can easily be doubled, so that the same resolution can be
79 displayed on different monitors, even if the horizontal
80 frequency specification differs. Note that this option
81 may not be supported by every frame buffer device
82
84 Generally a frame buffer display is organized as follows:
85 +---+---------------+---+---+
87 | | ^ | | |
88 | | | 5 | | |
89 | | v | | |
90 +---#################---+---+
91 | # ^ # | |
92 | # | # | |
93 | # | # | |
94 | 1 # | 2 # 3 | 4 |
95 |<->#<------+------>#<->|<->|
96 | # | # | |
97 | # | 6 # | |
98 | # | # | |
99 | # v # | |
100 +---#################---+---+
101 | | ^ | | |
102 | | | 7 | | |
103 | | v | | |
104 +---+---------------+---+---+
105 | | ^ | | |
106 | | | 8 | | |
107 | | v | | |
108 +---+---------------+---+---+
109 1 left margin
111 2 xres
112 3 right margin
113 4 horizontal sync len
114 5 upper margin
115 6 yres
116 7 lower margin
117 8 vertical sync len
118 The area bordered with `#' is the visible display area. Horizontal and
120 vertical frequencies can now easily be calculated, for this the sum of
121 horizontal or vertical values are important
122 htotal = left + xres + right + hslen
124 vtotal = upper + yres + lower + vslen
125 The length of one line can now be calculated with pixclock
127 line = pixclock * htotal
129 and we have the horizontal frequency
131 hfreq = 1E12 / line = 1E12 / (pixclock * htotal)
133 To get the vertical frequency vtotal must eventually adjusted. If the
135 display is laced, vtotal must be halved or if the display is a doubles‐
136 can one, vtotal must be doubled. Now we can calculate the length of one
137 frame
138 if (lace) vtotal /= 2
140 if (double) vtotal *= 2
141 frame = vtotal * line
143 and we get also the vertical frequency
145 vfreq = 1E12 / frame = hfreq / vtotal
147
150 fbset(8), fbdev(4)
151local Aug 1996 fb.modes(8)