Root/ubb-vga/README

1UBB-VGA - VGA-like output via UBB
2=================================
3
4Sources
5-------
6
7Timing and the idea for the voltage divider is from:
8http://faculty.lasierra.edu/~ehwang/public/mypublications/VGA Monitor Controller.pdf
9
10More timing parameters:
11http://tinyvga.com/vga-timing/640x480@60Hz
12
13For the signal assignment, see ubb-vga.sch
14Also available as a PDF:
15http://projects.qi-hardware.com/schhist/ubb-vga/pdf_ubb-vga.pdf
16http://en.wikipedia.org/wiki/VGA_connector
17
18
19Compatibility
20-------------
21
22Tested with the timing of commit 36861539431445b80e64f03218f352752338de52
23Timings will change in the future and may get better or worse. The
24purpose of this compatibility chart is to indicate what kind of results
25one can expect with different types of monitors.
26
27
28Display Monitor size Age (estimated)
29----------------------- --------------- ---------------
30Xenon XEN-1510T 15", 1024x768 ~9 years
31Samsung LN32R71B (TV) 32", 1360x768 ~5 years
32Samsung 206NW 20", 1680x1050 ~4 years
33LG W2243C 22", 1920x1080 ~1 year
34LG W2243L 22", 1920x1080 a few months
35
36Mode Monitor Image Hor. noise Cleanliness
37                  Stable Pixel FIFO
38--------------- --------------- --------------------------------------------
39640x480 XEN-1510T y y 1 20, 25% very distorted
40        LN32R71B y y 1 20, 25% very distorted
41        206NW y y 2-3 20, 20% very distorted
42        W2243C y y 2-3 20, 25% very distorted
43        W2243L y y 2-3 20, 20% very distorted
44
45640x480/58 XEN-1510T y y 1 large very distorted
46        LN32R71B y n 1 large very distorted
47        206NW y y 2-3 large distorted
48        W2243C y y 2-4 large very distorted
49        W2243L y y 2-3 large very distorted
50
51640x480/61 XEN-1510T y y 1 -/10, 20% very good/distorted (5)
52        206NW y y 2-4 - jittery, sometim. waves
53
54640x480/70 XEN-1510T y (2) 1 10, 25% distorted, flickery
55        LN32R71B n - "not supported mode"
56        206NW y (2) 3-8 - very jittery
57        W2243C n - "out of range"
58        W2243L n - "out of range"
59
60800x600/54 XEN-1510T n -
61        LN32R71B n - "not supported mode"
62        206NW y n (only flashes)
63        W2243C n - (screen stays dark)
64        W2243L n - (screen stays dark)
65
66800x600/56 XEN-1510T y (3) 1-2 - good
67        LN32R71B n - "not supported mode"
68        206NW y (1) 1-3 - jittery
69        W2243C y y 3-4 20, 50% unusable
70        W2243L y y 3-4 - very jittery with waves
71
72800x600/72 XEN-1510T y y 1-3 - good, slight flicker
73        LN32R71B y (4) 1 - image very good (4)
74        206NW y y 2-6 - jittery with bounces
75        W2243C n - (DMA lockup)
76        W2243L (not tried)
77
781024x768 XEN-1510T y y 1-2 good
79        LN32R71B n - "not supported mode"
80        206NW (not tried)
81        W2243C n - "out of range"
82        W2243L n - "out of range"
83
841024x768/53 XEN-1510T n - (screen stays dark)
85        LN32R71B n - "not supported mode"
86        206NW n - (screen stays dark)
87        W2243C n - (screen stays dark)
88        W2243L n - (screen stays dark)
89
901024x768/50 XEN-1510T y y 1-2 - good
91        LN32R71B n - "not supported mode"
92        206NW y y 2-4 - jittery
93        W2243C y y 3-5 - moves a lot
94        W2243L y y 3-5 - moves a lot
95
96Results:
97
98  Image does it show an image, yes/no ?
99  Stable is the image shown all the time or does the monitor
100        "catch" it only sometimes ?
101  Hor. noise horizontal jitter/vibration; distance in pixels
102    Pixel small pixel deviation, looking like analog noise
103    FIFO shift of a line or part of it by a large number of pixels
104
105For qualitative assessment, "jittery" means that the image is visible
106unstable but doesn't look too bad from a distance. "Bounces"/"waves"
107are deviations that appear in groups. "distorted" means that artefacts
108are visible. "good" means that the image has only small pixel jitter.
109
110Merely "jittery", "bounces", or "distorted" mean that the test image
111and the parameters it shows can be recognized. More severe problems
112mean that the test image looks clearly troubled. "Unusable" means
113that the screen content cannot be recognized.
114
115(1) Auto-sync places the image way too high. Can be corrected manually.
116(2) Image it stable but monitor shows a complaint (occasionally)
117(3) Auto-sync places the image too far to the left. Can be corrected
118    manually.
119(4) Places the image too far to the left. Cannot be sufficiently
120    corrected.
121(5) about 70% of all session have a clean stable image. The remaining
122    30% suffer significant FIFO noise.
123
124
125To do
126-----
127
128- use timer half interrupt and WAIT to synchronize (less bus traffic and
129  hopefully better granularity)
130- recover from DMA lockup
131- use color cube map (5x5x5 bits)
132- read/write raw frame buffer
133- consider prefetching first word of each line, to make DRAM controller
134  open the row and reduce DMA startup latency
135- add option to not disable the LCD (works with some modes if reducing
136  the LCD controller's burst size)
137- find out why 640x480 has so much FIFO noise
138- fix modes 800x600/54 and 800x600/72, broken by the timer change
139

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