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Old 07-29-2009, 07:39 PM   #1
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suspend to ram resuming ok with vbe post - what does it mean?

On my Debian 5.0 system whenever I tried to wake up from suspend mode, I use to get blank screen although my machine was alive (I can ssh, etc.). After doing some research I found that executing the command:
vbetool post
right after resuming from suspend gave me back my video. Now upon reading the man vbetool I got this info:
post vbetool will attempt to run BIOS code located at c000:0003. This is the code run by the system BIOS at boot in order to intialise the video hardware. Note that on some machines (especially laptops), not all of this code is present after system boot - as a result, executing this command may result in undefined behaviour. This command must be run from a text console, as it will otherwise interfere with the operation of X.
However I am looking for some more information on this and how does it work so that I can understand clearly as to why I need to issue the command to get back my video.

Does anybody knows a good pointer which explains what does VBE, POST, etc. mean?

Note that I am doing all this from a console mode.
Old 07-30-2009, 12:04 PM   #2
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'POST' stands for 'Power On Self Test' and is commonly used to mean 'kick the device into action, test yourself, come to life'. A fine example of POSTing is when you first turn on the machine, when you get the BIOS POST screen, where the memory is checked, etc..

Some video hardware and/or platforms do not properly kick the video card back into action and/or do not properly restore the video state as it was before you suspended.

VBEtool uses the LRMI (Linux Real Mode Interface) to do a couple assembly calls to the system BIOS interrupt routine, which in turn do an interrupt call to the video hardware, telling it to POST itself and come to life.

VBE stands for 'Video Bios Extention' if I remember correctly. VBEtool's purpose in life is to help these machines get their video sorted out, in such ways as resume/suspend issues, doing DPMS actions, turinig on/off the monitor or backlight, etc.

If you Google the 's2ram' tool and download/install it, you can configure it easily to perform the Video POST operation automatically, so you don't need to run the command blind from the console. Also, have a look into your BIOS on the computer-- some have a selection for whether or not to POST the video card after resume, and this might also work around (solve properly, actually) the issue.


Old 07-30-2009, 12:48 PM   #3
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Thank you for your detailed reply! It is by far a very comprehensive summary that I have come across the internet.

Also, have a look into your BIOS on the computer
Even I thought first that may be I should ask the BIOS guys to look into this. I do have easy access to the BIOS team. However I noticed that following also:

1. On suspending/resuming from console, I need the vbetool post command

2. On suspending/resuming from graphics mode (GNOME), if I Do Crtl+Alt+F1 (output still blank) and then Crtl+Alt+F7, I get my GNOME session back.

Also Windows XP resume just fine after suspend. Now that makes me think whether it is really a BIOS issue or a vga/graphics driver issue?


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