> However, the topic of port I/O and MMIO reminds me of some activity > by RayeR and others regarding low-level configuration to speed up > access to PCI / PCIe graphics in DOS. I think the issue was that no > fast defaults were applied by the BIOS, slowing down VESA LFB a lot.
Video is kind of a different animal than most other things. There is I/O that controls the hardware things like video modes, display resolutions, etc.), and that can be either MMIO or PMIO. But the memory-mapping of what actually gets displayed on screen (like segment B800h for color text modes) really isn't MMIO, and least not in the traditional sense. It is actually called dual-ported RAM or Video RAM, and allows both reads and writes from the CPU-side while also allowing the graphics hardware to read the same RAM at the same time so the graphics hardware knows what to display on the screen. Regular RAM can't do that. In addition, like MMIO, Video RAM can't be cached since that would effectively delay what the graphics hardware needs to see to know what to display on the screen. I do remember seeing some stuff from RayeR that I think was related to video and modifying something in the Model Specific Registers (MSRs) of the CPUs, but don't remember all the details. _______________________________________________ Freedos-devel mailing list Freedos-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/freedos-devel
