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Bochs VBE Extensions: Difference between revisions

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Bochs VBE Extensions (view source)

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== Programming the BGA ==
=== Writing values ===
To write an index/data pair to the BGA, you first write the index value to the 16-bit IO-port VBE_DISPI_IOPORT_INDEX (0x01CE), followed by writing the data value to the 16-bit IO-port VBE_DISPI_IOPORT_DATA (0x01CF). The BGA supports 10 different index values (0 through 9):
* VBE_DISPI_INDEX_ID (0)
* VBE_DISPI_INDEX_XRES (1)
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In order to change any of the registers (with the logical exception of VBE_DISPI_INDEX_ENABLE), the VBE extensions must be disabled first. To do so, write the value VBE_DISPI_DISABLED (0x00) to VBE_DISPI_INDEX_ENABLE (4). The changes are not visible until the VBE extensions are enabled again. To do so, write the value VBE_DISPI_ENABLED (0x01) to the same register (see also note below on enabling the LFB).
 
TODO: check whether we can read registers as well, and describe
 
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