Bochs VBE Extensions: Difference between revisions
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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). |
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). |
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TODO: check whether we can read registers as well, and describe |
[TODO: check whether we can read registers as well, and describe] |
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=== Setting display resolution and bit depth === |
=== Setting display resolution and bit depth === |
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Most likely, setting the display resolution and bit depth is all you need. To do so, disable the VBE extensions (see above), write the X resolution, Y resolution and BPP to their respective |
Most likely, setting the display resolution and bit depth is all you need. To do so, disable the VBE extensions (see above), write the X resolution, Y resolution and BPP to their respective registers (VBE_DISPI_INDEX_XRES (1), VBE_DISPI_INDEX_YRES (2) and VBE_DISPI_INDEX_BPP (3)) and enable the VBE extensions. Since the BGA is not real hardware, X and Y resolutions can be set at will [TODO: check whether Bochs does a sanity check and describe]. The bit depth needs to be one of the following: |
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* VBE_DISPI_BPP_4 (0x04) |
* VBE_DISPI_BPP_4 (0x04) |
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* VBE_DISPI_BPP_8 (0x08) |
* VBE_DISPI_BPP_8 (0x08) |
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For 24 BPP, the order of the colour components is blue first, then green, then red. [TODO: check for other BPP and describe] |
For 24 BPP, the order of the colour components is blue first, then green, then red. [TODO: check for other BPP and describe] |
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[TODO: some example code] |
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=== Using banked mode === |
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When using banked mode, the BGA uses a 64Kb bank size (VBE_DISPI_BANK_SIZE_KB) starting at address 0xA0000 (VBE_DISPI_BANK_ADDRESS). Banked mode is the default mode, so when enabling the VBE extensions without explicitly telling the BGA to use a linear frame buffer, the BGA enables banked mode. To set the bank to use, write the bank number to the bank register (VBE_DISPI_INDEX_BANK (5)). [TODO: check whether Bochs does a sanity check, or wrap-around, or whatever and describe] |
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=== Using a linear frame buffer (LFB) === |
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[[Category:Video]] |
[[Category:Video]] |
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