it's much easier to do it in programmable logic than with a microcontroller. Using the processor, ala Don Lancaster's "cheap video" approach is tempting, but useless if it can't do it all, and very precisely. At the 38 Khz VGA Hsync rate, 10 ns is not sufficient resolution unless you fiddle extensively with all the other parameters.

The usual approach is to build a timing loop based on an MCU clock that's derived from the "dot clock" that generates the edges on the VSync, then places the VBlank, HSync, HBlank, sync serrations (if needed) and loads the DAC at the precisly correct time. If it can't do that then it's not going to work out very well.

Lancaster did his "cheap video" with a 1 Mhz 6502, but didn't have to produce analog levels aside from what was produced by the rather simple video combiner, consisting of resistors and a transistor, and he used a shift register to generate the dots. VGA with variable pixel intensity doesn't allow that.

Once you go to some sort of programmable logic, you are better off, IMHO, omitting the MCU from the timing/pixel generation chain. Let the processor focus on what's going to be displayed, rather than on the mechanics of displaying it.

RE