Bochs VBE Extensions: Difference between revisions

When using a linear frame bufferframebuffer, the BGA exposes all of the graphicsvideo memory in a linearsingle fashion.linearly Inaddressable older versionssection of Bochs and QEMU the location is fixed at 0xE0000000 (VBE_DISPI_LFB_PHYSICAL_ADDRESS)memory. However, when Bochs is configured to emulate a PCI video card rather than an ISA one, theThe address of the framebuffer is no longernot fixed, butand canmust be read from the first [[PCI]] base address register (BAR 0 of device 0x1234:0x1111<!--[TODO: check behaviour for 4 BPP modes and QEMU]-->). To enable the LFBlinear framebuffer, use the VBE_DISPI_LFB_ENABLED flag (0x40) when enabling the VBEBGA extensionsin (soconjunction writewith athe valueVBE_DISPI_ENABLED offlag. VBE_DISPI_ENABLED<!--[TODO: |check VBE_DISPI_LFB_ENABLEDbehaviour (0x41)).for 4 BPP modes]-->

Unlike Bochs, QEMU does not necessarily pay attention to the VBE_DISPI_LFB_ENABLED flag. Bothwith respect to banked memory access, allowing both the linear frame bufferframebuffer and banked memory bankto arebe availableused at all times. Bochs payswill attention to the flag. In LFB mode itnot ignoreshonour requests to change the memory bank and nothing happens when youthe writelinear toframebuffer theis bankenabled, memory.and Init bankedwill modesimilarly nothingignore happensany whenwrites you writemade to the LFBmemory memorybank.

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