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Subject:  Re: [9front] strange behaviour of igfx and vesa
Date: Thu, 23 Jun 2016 15:43:38 +0900
From: kokamoto@hera.eonet.ne.jp
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I checked out all the output from vesa driver, and found
no missed registeres in igfx.c not including treatments of
sotware flag registers.

Then, I turned the direction to find chip differences from the
programming manual.   My chip belongs to DevBW, and
a working one to DevCL.   I found DebBW difference in
registers of [6200][6204][6110][70030][70034][72180],
the last three are not used in G45 in igfx.c.
The [6200][6204] are not important, because we are getting
the right values from those usage.
Then, the [6110] register, adps register, is the cause, I suppose.

In page 93, the manual says, in the case of DevBW, to enable 
the Analog display port, we must do a series of operations 
in the right order like:
1) set bit #31 to 1, and [11:10] to "11"
2) wait for VSYNC
3) clear [11:10] to "00"

Yes, I see large wait loop for Vsync in vesa drivers output.
like:
wport ff00 00070024 	# pipe A display status
rport ff04 00000000 	#	default value(no event)
wport ff04 00000002 	#	set to detect Vertical Blank Interrupt
wport ff00 00070024 	# pipe A display status
rport ff04 00000000 	#	done above set
		.....
wport ff00 00070024 	# pipe A display status
rport ff04 00000000 	#	no event (default)
rport 0061 00 	# PIT_CTL2
wport 0061 01 	# PIT_CTL2
wport 0043 b6 	# PIT_MODE
wport 0042 50 	# PIT_CNTR2
wport 0042 05 	# PIT_CNTR2
wport 0043 80 	# PIT_MODE
rport 0042 33 	# PIT_CNTR2
rport 0042 04 	# PIT_CNTR2
wport 0043 80 	# PIT_MODE
rport 0042 e3 	# PIT_CNTR2
rport 0042 00 	# PIT_CNTR2
wport 0043 80 	# PIT_MODE
rport 0042 cb 	# PIT_CNTR2
rport 0042 02 	# PIT_CNTR2
wport 0061 00 	# PIT_CTL2
		...
		...
wport ff00 00070024 	# pipe A display status
rport ff04 00000207 	#	State = Vsync occured, Start of VSYNC occured, VBLANK occured, Overlay Reg updated

However, there are output from/to many software flag registers
in this interval, I have been abondoned to deal with it, because
I have to investigate assembly codes. (sigh)

However, I got realized that the above 1) to 3) procedures
are not done in igfx.c.   Therefore, I think this is our
problem.  It may cause some large code rewriting.
How do you think?

Kenji