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1 perry 1 fb.modes
2 !!!fb.modes
3 NAME
4 DESCRIPTION
5 OPTIONS
6 INTERNALS
7 SEE ALSO
8 ----
9 !!NAME
10
11
12 fb.modes - frame buffer modes file
13 !!DESCRIPTION
14
15
16 ''/etc/fb.modes'' contains an unlimited number of video
17 mode descriptions. The general format of a video mode
18 is:
19
20
21 mode
22
23
24 geometry xres''''yres''
25 ''vxres''''vyres''
26 ''depth''''
27 timings ''pixclock''''left''
28 ''right''''upper''
29 ''lower''''hslen''
30 ''vslen''''
31 options__ __value''''
32
33
34 endmode
35 !!OPTIONS
36
37
38 geometry options:
39
40
41 ''xres''
42
43
44 visible horizontal resolution (in pixels)
45
46
47 ''yres''
48
49
50 visible vertical resolution (in pixels)
51
52
53 ''vxres''
54
55
56 virtual horizontal resolution (in pixels)
57
58
59 ''vyres''
60
61
62 virtual vertical resolution (in pixels)
63
64
65 ''depth''
66
67
68 display depth (in bits per pixel)
69
70
71 timing options:
72
73
74 ''pixclock''
75
76
77 length of one pixel (in picoseconds)
78
79
80 ''left''
81
82
83 left margin (in pixels)
84
85
86 ''right''
87
88
89 right margin (in pixels)
90
91
92 ''upper''
93
94
95 upper margin (in pixel lines)
96
97
98 ''lower''
99
100
101 lower margin (in pixel lines)
102
103
104 ''hslen''
105
106
107 horizontal sync length (in pixels)
108
109
110 ''vslen''
111
112
113 vertical sync length (in pixel lines)
114
115
116 other options:
117
118
119 the first value of this options is the default
120
121
122 __hsync__ {''low''|''high''}
123
124
125 the horizontal sync polarity
126
127
128 __vsync__ {''low''|''high''}
129
130
131 the vertical sync polarity
132
133
134 __csync__ {''low''|''high''}
135
136
137 the composite sync polarity
138
139
140 __extsync__ {''false''|''true''}
141
142
143 enable or disable external resync. If enabled the sync
144 timings are not generated by the frame buffer device and
145 must be provided externally instead. Note that this option
146 may not be supported by every frame buffer
147 device
148
149
150 __laced__ {''false''|''true''}
151
152
153 enable or disable interlace. If enabled the display will be
154 split in two frames, each frame contains only even and odd
155 lines respectively. These two frames will be displayed
156 alternating, this way twice the lines can be displayed and
157 the vertical frequency for monitor stays the same, but the
158 visible vertical frequency gets halved
159
160
161 __double__ {''false''|''true''}
162
163
164 enable or disable doublescan. If enabled every line will be
165 displayed twice and this way the horizontal frequency can
166 easily be doubled, so that the same resolution can be
167 displayed on different monitors, even if the horizontal
168 frequency specification differs. Note that this option may
169 not be supported by every frame buffer device
170 !!INTERNALS
171
172
173 Generally a frame buffer display is organized as
174 follows:
175
176
177 +---+---------------+---+---+
178 | | __^__ | | |
179 | | __|__ ''5'' | | |
180 | | __v__ | | |
181 +---#################---+---+
182 | # __^__ # | |
183 | # __|__ # | |
184 | # __|__ # | |
185 | ''1'' # __|__ ''2'' # ''3'' | ''4'' |
186 |____#____#____|____|
187 | # __|__ # | |
188 | # __|__ ''6'' # | |
189 | # __|__ # | |
190 | # __v__ # | |
191 +---#################---+---+
192 | | __^__ | | |
193 | | __|__ ''7'' | | |
194 | | __v__ | | |
195 +---+---------------+---+---+
196 | | __^__ | | |
197 | | __|__ ''8'' | | |
198 | | __v__ | | |
199 +---+---------------+---+---+
200
201
202 ''1'' left margin''
203 2'' xres''
204 3'' right margin''
205 4'' horizontal sync len''
206 5'' upper margin''
207 6'' yres''
208 7'' lower margin''
209 8'' vertical sync len
210
211
212 The area bordered with `#' is the visible display area.
213 Horizontal and vertical frequencies can now easily be
214 calculated, for this the sum of horizontal or vertical
215 values are important
216
217
218 htotal = left + xres + right + hslen
219 vtotal = upper + yres + lower + vslen
220
221
222 The length of one line can now be calculated with
223 pixclock
224
225
226 line = pixclock * htotal
227
228
229 and we have the horizontal frequency
230
231
232 hfreq = 1E12 / line = 1E12 / (pixclock *
233 htotal)
234
235
236 To get the vertical frequency vtotal must eventually
237 adjusted. If the display is laced, vtotal must be halved or
238 if the display is a doublescan one, vtotal must be doubled.
239 Now we can calculate the length of one frame
240
241
242 if (lace) vtotal /= 2
243 if (double) vtotal *= 2
244
245
246 frame = vtotal * line
247
248
249 and we get also the vertical frequency
250
251
252 vfreq = 1E12 / frame = hfreq / vtotal
253 !!SEE ALSO
254
255
256 fbset(8), fbdev(4)
257 ----
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