On 12.01.2022 6:37, Louis Ohland wrote:
Well, nobody seems to have read this and extracted the inner meaning.
I looked at your post but didn't have anything to add.
There's nothing new here...
Oddly enough, the Auxiliary Video Extension is gender-fluid. The > on-board VGA can pump VGA onto the AVE for use by an adapter in an AVE
-OR- BVE.
Umm, no, because BVE and planar video are mutually exclusive.
The video extension interconnect on planars w/o on-board video is just a passive bus - a set of lines. Their purpose is defined by the standard
and the adapter cards that adhere to this standard. The revised standard
puts what used to be a planar video to the BVE slot. The function of the
AVE remains the same.
The important part is that it's a replacement. You can't have a planar
video and a BVE extension in the same system because only one device can
act as the "base video" adapter. But you can theoretically have multiple
AVE devices. And this is something that IBM Japan put into practice. The
older PS/55 systems have a planar VGA subsystem which makes them
compatible with the PS/2 line. But for the Japanese market, they needed
another standard video subsystem - the "Display Adapter" board that can
handle Kanji characters in HW. The older AVEC Display Adapters don't
have an onboard VGA but instead, use the planar one... The thing is,
what if the customer wanted to use the 8514/A or some other adapter that
lacks onboard VGA? The Display Adapter board is capable of 1024x768, and
so is the 8514/A, but the modes aren't compatible, and neither is the
software interface. So they added another AVE slot to solve the problem.
Both AVE (VGA-less) adapters have access to the planar VGA, and there
are no conflicts because the AVE adapters are never active at the same
time (different modes, different iface).
If you were to allow multiple BVE adapters (remember they must implement
VGA), or a combination of an on-planar video and a BVE adapter (once
again, both VGA+), you would have a conflict between the two. (it would
be possible to resolve it in software, but for what purpose?)
Even though the video extension interconnect is just a passive bus, it
was necessary to define who is who (VGA vs. 8514/A, BVE vs. AVE...) -
for the reasons I've explained above. This was achieved by offsetting
the video extension by four pins in the case of the new BVE connector
(the four pins are the MME lines that are skipped for the original AVE).
Assuming you could findt a system with planar VGA and a BVE...
You won't.
(the only scenario that comes to mind is a BVE as a backup in case the
planar VGA subsystem fails... but that's kinda stretching it)
The card on the Auxiliary Video Extension CAN pump out VGA signals to
the planar DAC, and the planar DAC can display that video, BUT remember
the VGA is limited...
Yep, or vice-versa - which makes more sense because the AVE adapter will
have more capable RAMDAC in most implementations but will be capable of displaying the VGA modes as well - all that through one connector and
the same monitor.
https://ardent-tool.com/video/Video_Extension.html#Connector
Interesting, think of the Reply on-planar video...
Hmm, not sure what you mean there. Well, yes it's an SVGA with a more
capable RAMDAC, but how are you gonna use it? To allow for higher-spec
modes for some adapter that is limited by its own RAMDAC? That's
probably the only thing that comes to mind...
It's late, it's dark out, and I'm wearing sunglasses...
On 1/11/2022 16:24, Louis Ohland wrote:
https://ardent-tool.com/docs/pdf/15F2219_PS2_XGA_Display_Adapter_A_Technical_Reference_Sep90.pdf
Page 14 physical
With the XGA Display Adapter/A installed in the Base Video extension
slot, and enabled in VGA mode, digital video is supplied to the AVEC.
This allows pixel data, pixel clocks, synchronizing signals, and
blanking signals to be supplied to adapters that previously received
VGA video data from the integrated video subsystem.
XGA /A in BVEC [system WITHOUT on-board VGA] think of a Bermuda or 95.
VGA mode, digital video is supplied to the Aux Video extension.
This allows pixel data, pixel clocks, synchronizing signals, and
blanking signals to be supplied to adapters that previously received VGA
video data from the integrated video subsystem.
Comments: In VGA mode, the video generated by the XGA /A is compatible
with VGA.
Ye, it better be :) Especially since it's a BVE adapter...
When the XGA Display Adapter/A is in Extended Graphics mode, the pixel
data, pixel clock, and blanking signal lines are set to high
impedance, and the synchronizing signals run as set by the Extended
Graphics mode. In this condition the Auxiliary Video extension cannot
display Extended
Graphics video.
Extended Graphics mode, the pixel data, pixel clock, and blanking signal lines are set to high impedance, and the synchronizing signals run as
set by the Extended Graphics mode.
In this condition the Auxiliary Video extension cannot display Extended Graphics video.
Comment: The XGA /A sets the pixel stuff to high impedance. Not sure
about the sync signals being within the freq range supported by the AVEC.
It doesn't matter, it's "off the bus".
In system units without an integrated video subsystem where the XGA
Display Adapter/A is not installed in the Base Video extension slot,
digital video data is not supplied to the Auxiliary Video extension
slot. The XGA Display Adapter/A must be moved to the Base Video
extension slot if this function is required.
Plain language, XGA /A in normal slot, it cannot use Auxiliary Video extension. Wow, how could that be?
Ikr?!
Default VGA
In system units with Integrated video, if a display is attached to the
display connector, it is the default VGA display. Otherwise, the first
XGA Display Adapter/A (in numerical slot order) with a display
attached is the default VGA. All other XGA Display Adapter/A's in the
system unit are configured into Extended Graphics mode.
Here's the interesting stuff.
In systems with on-board video:
Display on planar video = Default VGA monitor
Display on XGA /A, no planar video = Default VGA monitor
All other XGA /A in system are in extended mode [they have to be]
That's really the only way to do it.
Comment: the XGA /A is unable to fit in the AVC.
In system units without integrated video, an XGA Display Adapter/A in
the Base Video extension slot with a display attached is the default
VGA. If a display is not attached under these conditions, or an XGA
Display Adapter/A is not installed in the Base Video extension, then
the first XGA Display Adapter/A in the system with a display attached
is the default VGA. All other XGA Display Adapter/A's in the system
unit are configured into Extended Graphics mode.
In Bermudas or 95s,
XGA /A in BVEC with a monitor is default VGA.
XGA /A not in BVEC, the first XGA /A with monitor is default VGA
All other XGA /As are configured in extended graphics mode
Again, the only logical way to do it. Or am I missing something?
There should be a comment about this somewhere on the Tool, but I'll
czech, as this is something that may be confusing for people that are
new to all this video extension stuff.
If, during the self-test and bring-up routine, an active VGA adapter is
detected that the XGA Display Adapter/A does not recognize, then all XGA
Display Adapter/A's are configured into Extended Graphics mode.
My SWAG at technoslovakian... XGA /A detects a strange VGA, and it
configures itself into extended graphics mode.
Essentially yes, but it will be implemented the other way around. First
look for any VIDEO ROMs and then check if they are XGA compatible. If
not it default to the "unknown VGA" behavior...
I have some of this documented in the T4 firmware, where it's further complicated by the "BIOS-less" IBM SVGA (and also by the on-board XGA-1
in model Model 90).
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