[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
Re: Using XFree86 With a Television
On Sun, 4 Apr 1999, Isaac Aaron wrote:
>Hi, dear ILUG members:
>
>I'm having difficulties in configuring Linux to use the TV out
>correctly.
The exact calculations require some knowledge of TV signals. I can help
you there. I have played with this before, using a SVGA->RCA adapter that
I'd built (for B/W only). It is also possible to use a SVGA->SCART adapter
for the same purpose (with color, but not over the air).
There is a set of XF86Config settings that describe exactly the settings
you want. Do a search on the net.
As a general rule of thumb, If Fpix is the clock, then Htotal = Fpix / 16525
(all in Hz). Also Tsync (the H sync pulse) should be exactly 5.6 usec (as
exactly as possible). The frame freq. MUST be 50 Hz. It is not practical
to use Fpix larger than 6 MHz, unless you oversample (if you don't know
what the hell I'm talking about, you need to do some serious reading on
TV signals and D/A techniques). The H/V ratio in TV is exactly 4:3, so you
can't have square pixels. There are also other interesting problems, like
interlacing, and what it does to moving aliased sprites at corners (top &
bottom).
Incidentally, 6MHz allows less than 640 pixels Horiz. Beyond that, the
bandwidth of the TV video amplifier will make your pixels illegible. You
need a good monitor to display more, and then the limited resolution of
the screen mask of a normal TV will be your limit.
Short answer: Buy a good large monitor or overhead projector ($ many K).
hope this helps ;)
Peter