HackingVGAforFun

VGA

Video Graphics Adapter

pinouts

VGA pinouts

build a fake monitor

• Terminate the color lines with 75ohms
• Attach a 24C02 serial eeprom to the specified pins (24c04 - 24c16 is possible to )
• if no eeprom is at hand, connect ID3 to GND

Modesetting

xrandr

To do so use xrandr:

xrandr --newmode "MODE1"   64.00  1400 1400 1401 1401 700 700 702 702 -hsync -vsync
xrandr --addmode VGA-0 "MODE1"
xrandr --output VGA-0 --mode "MODE1" --right-of LVDS

note: VGA-0 may not apply, it could be VGA1 or VGA too, depending on the driver.
note: the last command assumes LVDS to be your primary active connector, change depending on your system.

alternative arandr

Xorg.conf

Add a ModeLine to your Xorg.conf.

Section "Monitor"
       Identifier      "SyncMaster"
       Option          "VGA-0"
       HorizSync       30-96
       VertRefresh     50-160
       ModeLine        "MODE1" 64.00  1400 1400 1401 1401 700 700 702 702
EndSection

edid in eeprom

EDID I used EDID 1.3
Windows

• it accepts:
  • standart timings
  • established timings
• it looks like Windows XP doesn't like "prefered timings"

Linux

• The kernel module drm handels all the display stuff
• it accepts:
  • established timings
  • standart timings
  • prefered timings

flash a new edid

• Load the kernelmodule i2c-dev
• Get i2c-tools
• build the i2c-tools
• Become root: Sudo -s
• Add the tools folder to the PATH: PATH=$PATH:< ... >/i2c-tools/tools
• Run i2cdump to find the correct BUSID (device at 0x50 and 0x51)
• Flash new EDID with write-edid.sh
• Note the input file is plain/text with hexvalues, spaces and newlines only

create custom edid

• use Phoenix EDID Designer to create custom EDIDs

Note

• the tool outputs .dat-files, that need to be editet by hand, it contains invalid symbols
• you can use the export function to generate .raw files and use hexdump to convert them to plain/text hex

hack the kernel module drm for custom edid

This is neccessary if you specify hsync < 1 or vsync < 1 in your edid

• install linux-source
• install linux-kernel-headers
• modify the Makefile

all:
	$(MAKE) -C $(KDIR) M=$(PWD) modules
	cp drm.ko /lib/modules/`uname -r`/kernel/drivers/gpu/drm
	cp drm_kms_helper.ko /lib/modules/`uname -r`/kernel/drivers/gpu/drm
	chmod 755 /lib/modules/`uname -r`/kernel/drivers/gpu/drm
	update-initramfs -u

• patch drm_edid.c , it doesn't accept vsync_width OR hsync_width to be 0

Results

Mesa 9.0

Label	EDID Value	Description
AMD RV710	Vsync = 0	no graphics
AMD RV710	Vsync = 1	random graphics
AMD RV710	Htotal = Hactive	no graphics
AMD RV710	Hsync = 0	normal graphics
AMD RV710	Vtotal = Vactive + 2	random graphics

Links

• http://www.nathandumont.com/node/241