RE: [oc] Interested in developing CRT controller core

["Joe Zott" <jaz@itvc.com>]

I have done some work with CRT controllers to be used in video applications.

As a start I think the key design features and challenges are:
* Screen resolution (range)
* Sync frequency (range)
* Pixel format (need for look up tables etc.)
* Variability/scalability of design (need to support multiple clock
frequencies)
* Memory bandwidth requirements
* Intelligence (or just a dumb image plane)
* Compatibility with other designs / device driver model
* External interface (VGA only?)
* Internal interface (PCI for both control and memory?)

The range of applications to be supported and the environment where you want
to support them defines the specification. Any suggestions about the
environments that people want support for?

For my interests I propose that we limit ourselves to something relatively
modest. As an example of the design challenge the relatively modest point
requirement to support:
* 1024 x 768 screen resolution
* 60 Hz resolution
* 15 bit per pixel format with LUT to bring output up to 24 bits RGB

Leads to:
47 MHz pixel rate
378 MHz analog bandwidth (hint: only at the high end do you see
1024x768x60x8 performance - perhaps a 6bit DAC is more reasonable)
94 MB/s video memory bandwidth (for display only - need additional bandwidth
for screen updates) - how wide do we make it?
1.6 MB video memory
32Kx24 LUT memory @ 20 ns (for display only)

Increasing screen resolution and pixel color depth increases the resource
demands. Adding intelligence (2D / 3D functions) especially at these higher
display performance levels is very demanding.

I propose:
* 640x480, 800x600, 1024x768 screen resolution
* 60Hz, 72Hz, 75Hz, 85Hz sync frequency
* 256 color, 15bit, 16bit, 24bit, 32bit pixel formats
* We don't support the higher end of this (resolution/frequency/pixel depth)
* CRT controller has dedicated display memory
* Design is dumb, assume that processor could be dedicated if intelligence
is needed

Joe