Headless Device Video Driver Processing
During system startup, the video drivers are processed in the following order:
- If you include an OEM video driver in your run-time image, the OS attempts to load it.
- If the OEM video driver fails to load, typically because the video hardware for the OEM-specific driver is not installed, the OS attempts to load the VGA Save Driver, Vga.sys.
- If the VGA Save Driver fails to load, typically because there is no generic VGA-compatible video hardware, the OS attempts to load the Headless VGA Driver, Tsddd.dll.
If you have a device with no VGA adaptor but you include the VGA Save Driver in your configuration, the VGA Save Driver fails and the OS then loads the Headless VGA Driver.
To prevent a bug check from occurring, you must include the Headless VGA Driver in your configuration for the headless device to boot. Video output is enabled if you add a VGA card to your device, because the OEM Driver or VGA Save Driver is loaded rather than the Headless VGA Driver. In other words, if you add the Headless VGA Driver, your target system works with or without a VGA card installed; when you have a VGA card in the system, it is recognized and activated.
You can edit your run-time Boot.ini file for kernel mode debugging, and then verify that your image boots with no VGA card. This requires a motherboard that uses a version of BIOS that can function without a VGA card.
Last updated on Wednesday, October 18, 2006
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