Here's what happens when you unleash comprobe1() for com4 on a system
with a video chipset that emulates an IBM 8514A (e.g. Mach8, Mach32):

comprobe1() writes a zero to the IIR at 0x2ea.  In the 8514A, the
register at 0x2ea is called the DAC Mask register.  Its contents are
ANDed with all pixel data before it goes to the RAMDAC.  If its
contents are zero, then only zeros are written to the DAC, and you get
a blank screen.

This is Bad News.  COM4 has to go for the generic kernels.  Flipping a
DIP switch or reconnecting your modem is a lot easier than buying a
new video card (or a terminal).

(Information on 8514 taken from VGADOC3.ZIP, written by Finn
Thoegersen.)
-- 
Mike Long                                         Mike.Long@Analog.com
VLSI Design Engineer                              voice: (617)461-4030
Analog Devices, SPD Div.                            FAX: (617)461-3010
Norwood, MA 02062                            *this = !opinion(Analog);

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