hi,

i am working with a company that has the VGA,LCD project http://opencores.org/project,vga_lcd
embedded in a commercial SoC. the following resolutions and bpp have been successfully demonstrated:

800x600 @ 32bpp 60hz
640x480 @ 32bpp 60hz
1024x768 @ 16bpp 53hz
1024x768 @ 8bpp 60hz
1280x768 @ 8bpp 60hz
1440x900 @ 8bpp 60hz but with completely wrong sync offsets resulting in either the first few rows disappearing off-screen, or the top-left pixel actually being in the bottom-right corner.

now, the reason why we had to drop to 53hz on 1024x768 @ 16bpp is because there is a problem somewhere with the wishbone 2 bus simply not being fast enough to supply memory access quickly enough. at 15bpp 60hz there are continous IRQ errors coming in, requiring resets, resulting in the LCD monitor dropping in and out. at 8bpp these errors go away as the memory rate required is, obviously, halved.

in exploring the 1440x900 resolutions, the experience of endeavouring to map the timings listed here:
http://tinyvga.com/vga-timing/1440x900@60Hz to actual VGA/LCD parameters was, again, a reminder of the extreme difficulty (2 days) in finding a working mapping for the 1024x768 timings, and that difficulty is something i do not really wish to replicate.

whilst experimenting to find the 1024x768 parameters i found that *in no way* do the names of the standard conventions for timings (as listed in the above web page) match the names of the VGA/LCD memory-mapped parameters. the actual parameters placed into the driver were very far removed from anything resembling what could be seen on the above web page.

so my question is: could someone who understands the VGA/LCD core kindly provide an algorithmic 100% reproducible equation where one might expect to take standard timings for VGA screens and create, with 100% reliability, the values needed to be put into the VGA/LCD core?

many thanks.

l.

Not a complete answer to your question, but if it's any help, this is
how I calculated the parameters in the Linux kernel driver:
https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/tree/drivers/video/fbdev/ocfb.c#n125

And the values used there comes from this table:
https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/tree/drivers/video/fbdev/core/modedb.c#n36