ubb-vga/README: moved old content away and added new compatibility test results

- README.old: moved old content here
- README: updated and extended compatibility chart

ubb-vga/README.old

@@ -0,0 +1,83 @@
+UBB-VGA - VGA-like output via UBB
+=================================
+
+*** THIS IS THE README FOR AN OLDER VERSION OF THE HARDWARE AND THE DRIVER ***
+
+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
+
+
+Signal	8:10	VGA
+-------	-------	---
+R	DAT2	1
+VSYNC	DAT3	14
+HSYNC	CMD	13
+G	DAT0	2
+B	DAT1	3
+GND	GND	5
+
+http://en.wikipedia.org/wiki/VGA_connector
+
+
+Timing
+------
+
+Since the Ingenic CPUs take about 8.5 PCLK cycles for a GPIO set or clear,
+and we can only set or clear a set of signals in GPIO operation, but not
+set some and clear others, we cannot have a real 320 horizontal pixels.
+
+Instead, set and clear operations alternate. This means that the best-case
+resolution is equivalent to 320 pixels (if the original pixel boundaries
+coincide with the set/clear phases), but it can be as low as 160 pixels if
+the boundaries don't match.
+
+Furthermore, timing is still a bit too tight. We therefore use a pixel
+clock that's about 10% slower than the original. Luckily, most monitors
+don't mind.
+
+
+Single/double mode
+------------------
+
+In single mode, only one set/clear can be performed per pixel. They are
+arranges such that the first pixel can only turn on channels, the
+following pixel can only turn off channels, and so on.
+
+In double mode, a set and a clear is performed per pixel. This changes
+the timing such that it differs substantially from VGA, but some
+monitors can still synchronize with this.
+
+The resulting signals for various bit patterns are shown in mapping.fig
+Each group shows the input pixels, and signal for single mode, and the
+signal for double mode. "S" indicates a point where the channel can be
+turned on, "C" indicates a point where it can be turned off.
+
+Note that there are probably other mapping algorithms that would yield
+better results. The mapping is not a very performance-critical part of
+ubb-vga. Improvements are welcome.
+
+
+Compatibility
+-------------
+
+ubb-vga in single mode has been tested with the following monitors:
+
+Display			Monitor size	Quality
+-----------------------	---------------	----------------------------------
+Xenon XEN-1510T		15", 1024x768	good
+Samsung 206NW		20", 1680x1050	poor (horizontal instability)
+LG W2243C		22", 1920x1080	acceptable (slight instability)
+LG W2243L		22", 1920x1080	acceptable (slight instability)
+
+In double mode:
+
+Display			Pixels missing	Quality
+			left/right
+-----------------------	---------------	------------------
+Xenon XEN-1510T		5 / 25		good