VGA to DVI conversion (HP Microserver Gen8)…

AllanGreen

New Member


Messages: 5

Hi, I've looked around the web without any luck, but I have my fingers crossed! I have been running a NAS4Free server on FreeBSD 11.1 for some time now without any problems. Finally I've got round to tidy up my cabling with a DVI KVM switch and (as Gen8 users will know) have only a VGA output from it. I've now invested in two different VGA to DVI converters, and neither works, though the VGA signal on its own is fine when I take it direct to the monitor. I've plugged the converters into a laptop and they work fine under windows. I've also tried taking the DVI signal direct to the monitor without the kvm and that doesn't work either! Anyone got any ideas? I am completely befuddled... Thanks for reading!
 

rsronin

Member

Reaction score: 60
Messages: 75

AllanGreen, I agree with VladiBG, buy a low profile video card. I have this on both a N40L and N54L. When the N54l was my main machine it even had a low profile Radeon HD7750 without problems. Now they are both happy with a fanless low profile NVidia card. For suggestions.
 

aragats

Daemon

Reaction score: 438
Messages: 1,064

I've plugged the converters into a laptop and they work fine under windows.
Do you have different video modes in FreeBSD and MS Windows?
If you're in console mode (no graphics), most likely, the video mode is different. If so, that means your VGA-DVI converters do not support certain modes.
You may try changing FreeBSD video mode.
 
OP
OP
A

AllanGreen

New Member


Messages: 5

Hi everyone, thanks so much for all your replies. Yes, the use of a DVI card had occurred to me but unfortunately the Gen8 only has one expansion card slot and I'm already using it for a decent 4-port disk controller. I do like the idea of changing the video mode. I'll report back once I've tried that. I never imagined there was any control of default video mode but now I think about it I imagine there must be! Will let you all know! Allan.
 
OP
OP
A

AllanGreen

New Member


Messages: 5

Oh, and just in case it is of any relevance, I have discovered that I have exactly the same problem when I try to use the vga output of my esxi server. On that machine however I have a few spare slots and I have a PCI card waiting to be fitted.... However the console mode on whatever Linux derivative is used by esxi may not be so easy to fix... :)
 

olli@

Well-Known Member
Developer

Reaction score: 229
Messages: 262

Note that DVI is not the same as DVI.

DVI can have analog signals (DVI-A), digital signals (DVI-D), or both (DVI-I). Your VGA-to-DVI converter is probably generating analog signals only (because VGA is always analog). Maybe your KVM and/or monitor support digital DVI only. In this case you have to use a converter that includes an analog-to-digital conversion (A/D). I'm not sure if these even exist. Another workaround would be to use two converters: VGA-to-HDMI plus HDMI-to-DVI: Because HDMI is digital only, that converter must always include analog-to-digital conversion. I haven't tried something like that myself, though, so no guarantees …

See the Wikipedia article on DVI for more information.
 
OP
OP
A

AllanGreen

New Member


Messages: 5

Thank you Olli. Both my converters are active (or at least they require external power!) so I'm assuming that they include the necessary ADCs. It is interesting that everything worked when fed with the vga output of a Windows laptop, and I'm using DVI-D (dual link) cables (which do not include the C1 - C4 analogue signals). They both arrived without any detailed technical information (of course). One came from CPC, the other from Amazon. If the video mode gets me nowhere I'll open them up and see if there is any chipset data I can discover :)
 
OP
OP
A

AllanGreen

New Member


Messages: 5

Solution! Aragats was correct. The console was operating in text mode, which does not seem to suit the VGA/DVI converters. Following the vidcontrol instructions in the FreeBSD handbook, I issued (while temporarily connected with a VGA cable!)

vidcontrol MODE_272

(this is a 16 colour 600x800 mode) and suddenly everything worked. I've also modified the rc.conf to include this line:

allscreens_flags="MODE_272"

but I daren't restart the file server pending user logout, so this has yet to be tested.

One other thing to bear in mind... the converter I'm using uses 5v from an otherwise unused USB port. I haven't checked this properly yet but as part of my initial experimentation I turned on the 5V supply to ALL the usb sockets (not knowing which one is which!) with usbconfig.

usbconfig -u 0 -a N power_on

where N is the port ID, so I set 2,3, and 4 on... Maybe this was not required...

Thank you all for your time and patience, good to know this resource exists!
 
Top