Hi, according to
the trick to boot without monitor attached and then stay in BIOS
modes (e.g. using VESA modes, not Linux lowlevel drivers) to stay
in TV-out mode is quite common. For Voodoo3, some i2c bus is mentioned
which configures the port.

A full explanation for Linux can be found here:
You use lm_sensors-2.5.5 and i2c-2.5.5 or newer...
The kernel needs i2c "i2c support", "i2c bit banging" and "i2c devices",
and you need the usual 3dfx stuff (agpart, DRI, 3dfx banshee/Voodoo3+).

You also need a mode which a TV can understand, e.g.:
ModeLine "640x480PAL"   29.50       640  675  678  944  480  530  535  625
ModeLine "800x600PAL"   36.00       800  818  820  960  600  653  655  750
Some DOS tools should be able to process those, but I guess once you
enabled TV mode, the BIOS will take care to use TV compatible refresh rates.

The sensors-detect tool will find the i2c-voodoo3 thing and possibly the
PiiX of your motherboard, for which you can add driver modules. It would
also detect the i2c chips w83781d and generic eeprom... For Voodoo, only
i2c-core, i2c-algo-bit and i2c-voodoo3 are needed...
You also enable a bt869 module for the TV modulator...
But you have to enable something in the chip, e.g.
/proc/sys/dev/sensors/bt869-i2c-0-44 which involves test screen,
bit per pixel, ntsc/pal, resolution and status stuff...
For some reason, turning colorbars (test screen) on and off seems to get
the chip into sane state... Summary:

  # /sbin/modprobe -v i2c-voodoo3
  # /sbin/modprobe -v bt869
  # echo 800 600 > /proc/sys/dev/sensors/bt869*/res
  # echo 0 > /proc/sys/dev/sensors/bt869*/ntsc
  # cat /proc/sys/dev/sensors/bt869*/colorbars

(reading colorbars status seems to be enough...)

To get anything useful out of this DOS wise, you will have to find
some i2c editing or diagnostics tool. You might even need some BT869
driver. But hey, you are an experienced DOS and google user I assume ;-).

Hopefully some people on this list have experience with BT869 or i2c and
can send some more hints.


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