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113 lines
4.0 KiB
Plaintext
113 lines
4.0 KiB
Plaintext
UBB-VGA - VGA-like output via UBB
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=================================
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Sources
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-------
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Timing and the idea for the voltage divider is from:
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http://faculty.lasierra.edu/~ehwang/public/mypublications/VGA Monitor Controller.pdf
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More timing parameters:
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http://tinyvga.com/vga-timing/640x480@60Hz
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For the signal assignment, see ubb-vga.sch
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Also available as a PDF:
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http://projects.qi-hardware.com/schhist/ubb-vga/pdf_ubb-vga.pdf
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http://en.wikipedia.org/wiki/VGA_connector
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Compatibility
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-------------
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Tested with the timing of commit 36861539431445b80e64f03218f352752338de52
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Timings will change in the future and may get better or worse. The
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purpose of this compatibility chart is to indicate what kind of results
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one can expect with different types of monitors.
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Display Monitor size Age (estimated)
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----------------------- --------------- ---------------
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Xenon XEN-1510T 15", 1024x768 ~9 years
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Samsung 206NW 20", 1680x1050 ~4 years
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LG W2243C 22", 1920x1080 ~1 year
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LG W2243L 22", 1920x1080 a few months
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Mode Monitor Image Hor. noise Cleanliness
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Stable Pixel FIFO
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--------------- --------------- --------------------------------------------
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640x480 XEN-1510T y y 1 20, 25% very distorted
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206NW y y 2-3 20, 20% very distorted
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W2243C y y 2-3 20, 25% very distorted
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W2243L y y 2-3 20, 20% very distorted
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640x480/58 XEN-1510T y y 1 large very distorted
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206NW y y 2-3 large distorted
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W2243C y y 2-4 large very distorted
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W2243L y y 2-3 large very distorted
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640x480/70 XEN-1510T y (2) 1 10, 25% distorted, flickery
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206NW y (2) 3-8 - very jittery
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W2243C n - "out of range"
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W2243L n - "out of range"
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800x600/54 XEN-1510T n -
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206NW y n (only flashes)
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W2243C n - (screen stays dark)
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W2243L n - (screen stays dark)
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800x600/56 XEN-1510T y (3) 1-2 - good
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206NW y (1) 1-3 - jittery
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W2243C y y 3-4 20, 50% unusable
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W2243L y y 304 - very jittery with waves
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800x600/72 XEN-1510T y y 1-3 - good, slight flicker
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206NW y y 2-6 - jittery with bounces
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W2243C n - (DMA lockup)
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W2243L (not tried)
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1024x768 XEN-1510T y y 1-2 good
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206NW (not tried)
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W2243C n - "out of range"
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W2243L n - "out of range"
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1024x768/53 XEN-1510T n - (screen stays dark)
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206NW n - (screen stays dark)
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W2243C n - (screen stays dark)
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W2243L n - (screen stays dark)
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1024x768/50 XEN-1510T y y 1-2 - good
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206NW y y 2-4 - jittery
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W2243C y y 3-5 - moves a lot
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W2243L y y 3-5 - moves a lot
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Results:
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Image does it show an image, yes/no ?
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Stable is the image shown all the time or does the monitor
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"catch" it only sometimes ?
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Hor. noise horizontal jitter/vibration; distance in pixels
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Pixel small pixel deviation, looking like analog noise
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FIFO shift of a line or part of it by a large number of pixels
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For qualitative assessment, "jittery" means that the image is visible
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unstable but doesn't look too bad from a distance. "Bounces"/"waves"
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are deviations that appear in groups. "distorted" means that artefacts
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are visible. "good" means that the image has only small pixel jitter.
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Merely "jittery", "bounces", or "distorted" mean that the test image
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and the parameters it shows can be recognized. More severe problems
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mean that the test image looks clearly troubled. "Unusable" means
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that the screen content cannot be recognized.
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(1) Auto-sync places the image way too high. Can be corrected manually.
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(2) Image it stable but monitor shows a complaint (occasionally)
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(3) Auto-sync places the image too far to the left. Can be corrected
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manually.
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To do
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-----
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- use timer half interrupt and WAIT to synchronize (less bus traffic and
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hopefully better granularity)
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- recover from DMA lockup
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- use color cube map (5x5x5 bits)
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- read/write raw frame buffer
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- consider prefetching first word of each line, to make DRAM controller
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open the row and reduce DMA startup latency
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- add option to not disable the LCD (works with some modes if reducing
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the LCD controller's burst size)
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- find out why 640x480 has so much FIFO noise
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- fix modes 800x600/54 and 800x600/72, broken by the timer change
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