![]() ![]() To do so, write the value VBE_DISPI_ENABLED (0x01) to the same register (see also note below on enabling the LFB). The changes are not visible until the VBE extensions are enabled again. To do so, write the value VBE_DISPI_DISABLED (0x00) to VBE_DISPI_INDEX_ENABLE (4). In order to change the contents of registers 1-3 (VBE_DISPI_INDEX_XRES, VBE_DISPI_INDEX_YRES, VBE_DISPI_INDEX_BPP) the VBE extensions must be disabled first. The BGA supports 10 different index values (0 through 9): To write an index/data pair to one of the BGA registers, first write its 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). 0xB0C3 - support for getting capabilities, support for using 8 bit DAC.0xB0C2 - 15, 16, 24 and 32 BPP modes, support for linear frame buffer, support for retaining memory contents on mode switching.0xB0C1 - virtual width and height, X and Y offset.0xB0C0 - setting X and Y resolution and bit depth (8 BPP only), banked mode.Six versions of the BGA have existed, of which 0xB0C5 is the current version (as of 2009, Bochs version 2.4). They are used in the sections below, with their numerical value between parentheses.Īs Bochs has evolved, so has the BGA. The names of these defines all start with VBE_DISPI. The Bochs sources define in vga.h, located in the subdirectory iodev/, a number of defines that are useful for programming the BGA. QEMU (with the -std-vga command line argument) also uses the latest version. There are six versions of the BGA (0xB0C0 through 0xB0C5), but if you use the latest version of Bochs you only need to concern yourself with the latest one (0xB0C5). Via these ports it is possible to enable or disable the VBE extensions, change the screen resolution and bit depth, and manage a larger virtual screen. The first one is an index port, the second one a data port (comparable to how the VGA handles its sets of registers). The Bochs emulated graphics hardware (henceforth called BGA for Bochs Graphics Adaptor) is accessed via two 16-bit IO-ports. 3.4 Setting display resolution and bit depth.Apparently, the VMWare format for disks is popular because several emulators support it.They start small when the emulated disk is empty and expand as more data is written. Growing images are similar to sparse images.Journaling images keep track of changes made by each session, and they can be undone/redone in order.Useful if you want to remove any changes to a "good" disk. Any changes are stored in a new image that is layered on top. Stackable images allow a "base" read-only image.A sparse image does not store blank space, so you could emulate a 1 GB hard disk, but it would only take up 200 MB of space if it had 800 MB free space.The concatenated format allows several separate files to emulate one combined hard disk useful for partitions.A flat image offers no special features and takes up the full amount of disk space that it emulates.The emulators usually support only a flat image for a floppy and an ISO image file for CD-ROMs. This chart shows the file formats for an emulated hard disk. VBE, OpenGL virtualization, VGA (decent), BGA, VBoxVideo VBE, VGA (partial), Cirrus Logic GD54xx, (BGA?) VBE, VGA (partial), BGA, Cirrus Logic GD54xx Yes: ARM, SPARC, MIPS, MIPS64, m68k, PowerPC Maybe (yes for PowerPCs, no for Intel Macs) It can't hurt to use more than one emulator (or several), in order to test your OS on a variety of platforms without using real hardware. This comparison is just to point out their differences. None of them are necessarily "better" than the others. Bochs is by far the slowest, but that is because of its full emulation, which gives it the highest accuracy. Overall, VirtualBox offers the richest set of features, along with very fast performance. Virtualization, Emulation on legacy devices Web interface, non-free Windows client (VI3) Virtualization (on PC), Emulation (on Mac) Command line, script file, interactive menus ![]()
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