Re: [Discuss-gnuradio] VGA-based DVB-T modulator

[John Gilmore]

> Does anyone here know if the VGA cards prevent you from controlling
> the DAC durinng the blanking intervals?  Are the blanking intervals
> implemented in hardware or in software?

Generally, video cards stop squirting bits during the blanking intervals,
which are implemented in software.  This lets the adjacent rows of the
frame buffer be next to each other in the memory that the video hardware
is scanning its way through.

However, the timing of the blanking intervals can be controlled with a
fair bit of detail.  These are those terrible X config "modeline"
values that can blow up your monitor if you set them wrongly.  There
will be *some* blanking interval, but it can perhaps be very short and
can perhaps occur at an interval that won't often affect your signal.

It would be great if video hardware had a mode that turned off this
foolishness and just kept scanning out a section of RAM, raw.  This
would even improve refresh rates on things like LCDs that don't have
to move an electron beam back across the screen during the "horizontal
retrace" time.  But few video chips probably do.

        John