HackingVGAforFun

HackingVGAforFun

This site describes how to fool around with the VGA Controller.

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

To set a custom mode either use xrandr or xorg.conf or selfbuild eeprom VGA adapter.

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

monitor edid

Add a 24C02 EEPROM to a VGA connector. This EEPROM contains the EDID.

I used EDID 1.3
Windows Xp

• accepts
  • standart timings
  • established timings
• regrets
  • prefered timings

Windows Vista and newer

• accepts
  • standart timings
  • established timings
• regrets
  • TODO

Linux

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

hack the kernel module drm for custom edid

This is only neccesarry for custom EDIDs inside the "monitors" EEPROM. Using either the Xorg.conf method or the xrandr method doesn't need modification to the drm kernel module. It is only neccessary if you specify hsync < 1 or vsync < 1 in your EDID.

• on debian
  • install linux-source
  • install linux-kernel-headers
  • append to the drm Makefile and run make

all:
	$(MAKE) -C $(KDIR) M=$(PWD) modules
	cp *.ko /lib/modules/`uname -r`/kernel/drivers/gpu/drm
	cp nouveau/*.ko /lib/modules/`uname -r`/kernel/drivers/gpu/drm/nouveau
	cp radeon/*.ko /lib/modules/`uname -r`/kernel/drivers/gpu/drm/radeon
	cp via/*.ko /lib/modules/`uname -r`/kernel/drivers/gpu/drm/via
	cp gma500/*.ko /lib/modules/`uname -r`/kernel/drivers/gpu/drm/gma500
	cp i915/*.ko /lib/modules/`uname -r`/kernel/drivers/gpu/drm/i915
	chmod 755 /lib/modules/`uname -r`/kernel/drivers/gpu/drm
	update-initramfs -u

• on fedora
  • install kernel-sources
  • append to the drm Makefile and run make

KDIR    := /lib/modules/$(shell uname -r)/build
all:
	$(MAKE) -C $(KDIR) M=$(PWD) modules
	cp *.ko /lib/modules/`uname -r`/kernel/drivers/gpu/drm
	cp nouveau/*.ko /lib/modules/`uname -r`/kernel/drivers/gpu/drm/nouveau
	cp radeon/*.ko /lib/modules/`uname -r`/kernel/drivers/gpu/drm/radeon
	cp via/*.ko /lib/modules/`uname -r`/kernel/drivers/gpu/drm/via
	cp gma500/*.ko /lib/modules/`uname -r`/kernel/drivers/gpu/drm/gma500
	cp i915/*.ko /lib/modules/`uname -r`/kernel/drivers/gpu/drm/i915
	chmod 755 /lib/modules/`uname -r`/kernel/drivers/gpu/drm
	dracut -f /boot/initramfs-currentimage

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

how to flash a new edid into monitor eeprom

• remove fglrx or fglrx-legacy, make sure mesa is running !
• 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

how to build custom edid

• download edid from monitor
  • Linux: use i2c-get
  • Windows: Registry or Phoenix EDID Designer
• use Phoenix EDID Designer to create custom EDIDs
  • Note: it runs under WINE

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

Tests

Test system

• Linux 3.11.6 x86_64
• Mesa 9.2.0
• Intel(R) Core(TM)2 Quad CPU Q9300 @ 2.50GHz
• 4GByte DDR2 Memory

Results

Vendor	Name	Codename	Driver	VRAM [MB]	max bandwidth [MB/s]	min vsync	min hsync	min vblank	min hblank	Optional
Nvidia	Geforce 8600GTS	NV84	Mesa 9.2.0	256	310	1*	1*	1*	1*	hsync + hblank >= 1, vsync + vblank >= 1, every second frame is blank if (vsync + vblank) = 1 or (hsync + hblank) = 1
ATI	Radeon HD4850	RV770	Mesa 9.2.0	512	390	2	1*	0	1*	hsync + hblank >= 1, either of one can be zero
ATI	Radeon HD4350 mobility	RV710	fglrx 8.92	512	-	2	1	0	1
Intel(R)	Ivybridge Desktop	GT1	Mesa 9.2.0	???	1400		0	12	0	4	hsync + hblank >= 12, vsync + vblank >= 4

Recommended Modelines

• NV84 56.00 1024 1025 1025 1026 768 766 767 769

Links

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