UBB-VGA - VGA-like output via UBB
=================================
Sources
-------
Timing and the idea for the voltage divider is from:
http://faculty.lasierra.edu/~ehwang/public/mypublications/VGA Monitor Controller.pdf
More timing parameters:
http://tinyvga.com/vga-timing/640x480@60Hz
For the signal assignment, see ubb-vga.sch
Also available as a PDF:
http://projects.qi-hardware.com/schhist/ubb-vga/pdf_ubb-vga.pdf
http://en.wikipedia.org/wiki/VGA_connector
Compatibility
-------------
Tested with the timing of commit 36861539431445b80e64f03218f352752338de52
Timings will change in the future and may get better or worse. The
purpose of this compatibility chart is to indicate what kind of results
one can expect with different types of monitors.
Display Monitor size Age (estimated)
----------------------- --------------- ---------------
Xenon XEN-1510T 15", 1024x768 ~9 years
Samsung LN32R71B (TV) 32", 1360x768 ~5 years
Samsung 206NW 20", 1680x1050 ~4 years
LG W2243C 22", 1920x1080 ~1 year
LG W2243L 22", 1920x1080 a few months
Mode Monitor Image Hor. noise Cleanliness
Stable Pixel FIFO
--------------- --------------- --------------------------------------------
640x480 XEN-1510T y y 1 20, 25% very distorted
LN32R71B y y 1 20, 25% very distorted
206NW y y 2-3 20, 20% very distorted
W2243C y y 2-3 20, 25% very distorted
W2243L y y 2-3 20, 20% very distorted
640x480/58 XEN-1510T y y 1 large very distorted
LN32R71B y n 1 large very distorted
206NW y y 2-3 large distorted
W2243C y y 2-4 large very distorted
W2243L y y 2-3 large very distorted
640x480/61 XEN-1510T y y 1 -/10, 20% very good/distorted (5)
206NW y y 2-4 - jittery, sometim. waves
640x480/70 XEN-1510T y (2) 1 10, 25% distorted, flickery
LN32R71B n - "not supported mode"
206NW y (2) 3-8 - very jittery
W2243C n - "out of range"
W2243L n - "out of range"
800x600/54 XEN-1510T n -
LN32R71B n - "not supported mode"
206NW y n (only flashes)
W2243C n - (screen stays dark)
W2243L n - (screen stays dark)
800x600/56 XEN-1510T y (3) 1-2 - good
LN32R71B n - "not supported mode"
206NW y (1) 1-3 - jittery
W2243C y y 3-4 20, 50% unusable
W2243L y y 3-4 - very jittery with waves
800x600/72 XEN-1510T y y 1-3 - good, slight flicker
LN32R71B y (4) 1 - image very good (4)
206NW y y 2-6 - jittery with bounces
W2243C n - (DMA lockup)
W2243L (not tried)
1024x768 XEN-1510T y y 1-2 good
LN32R71B n - "not supported mode"
206NW (not tried)
W2243C n - "out of range"
W2243L n - "out of range"
1024x768/53 XEN-1510T n - (screen stays dark)
LN32R71B n - "not supported mode"
206NW n - (screen stays dark)
W2243C n - (screen stays dark)
W2243L n - (screen stays dark)
1024x768/50 XEN-1510T y y 1-2 - good
LN32R71B n - "not supported mode"
206NW y y 2-4 - jittery
W2243C y y 3-5 - moves a lot
W2243L y y 3-5 - moves a lot
Results:
Image does it show an image, yes/no ?
Stable is the image shown all the time or does the monitor
"catch" it only sometimes ?
Hor. noise horizontal jitter/vibration; distance in pixels
Pixel small pixel deviation, looking like analog noise
FIFO shift of a line or part of it by a large number of pixels
For qualitative assessment, "jittery" means that the image is visible
unstable but doesn't look too bad from a distance. "Bounces"/"waves"
are deviations that appear in groups. "distorted" means that artefacts
are visible. "good" means that the image has only small pixel jitter.
Merely "jittery", "bounces", or "distorted" mean that the test image
and the parameters it shows can be recognized. More severe problems
mean that the test image looks clearly troubled. "Unusable" means
that the screen content cannot be recognized.
(1) Auto-sync places the image way too high. Can be corrected manually.
(2) Image it stable but monitor shows a complaint (occasionally)
(3) Auto-sync places the image too far to the left. Can be corrected
manually.
(4) Places the image too far to the left. Cannot be sufficiently
corrected.
(5) about 70% of all session have a clean stable image. The remaining
30% suffer significant FIFO noise.
To do
-----
- use timer half interrupt and WAIT to synchronize (less bus traffic and
hopefully better granularity)
- recover from DMA lockup
- use color cube map (5x5x5 bits)
- read/write raw frame buffer
- consider prefetching first word of each line, to make DRAM controller
open the row and reduce DMA startup latency
- add option to not disable the LCD (works with some modes if reducing
the LCD controller's burst size)
- find out why 640x480 has so much FIFO noise
- fix modes 800x600/54 and 800x600/72, broken by the timer change
9942f62cb8