| VBE Display API |
| ------------------------------------------------------------------------------------------------------------- |
| This document is part of the Bochs/VBEBios documentation, |
| it specifies the bochs host <-> vbebios client communication. |
| |
| That means, the display code implementation and the vbebios code depend |
| very heavily on each other. As such, this documents needs be synchronised |
| between bochs CVS and the vgabios CVS. |
| |
| This document does not describe how the VBEBios implements the VBE2/3 spec. |
| This document does not describe how the Bochs display code will display gfx based upon this spec. |
| |
| |
| API History |
| ----------- |
| 0xb0c0 supports the following VBE_DISPI_ interfaces (present in Bochs 1.4): |
| VBE_DISPI_INDEX_ID |
| VBE_DISPI_INDEX_XRES |
| VBE_DISPI_INDEX_YRES |
| VBE_DISPI_INDEX_BPP |
| VBE_DISPI_INDEX_ENABLE |
| VBE_DISPI_INDEX_BANK |
| |
| Bpp format supported is: |
| VBE_DISPI_BPP_8 |
| |
| 0xb0c1 supports 0xb0c0 VBE_DISPI_ interfaces, additional interfaces (present in Bochs 2.0): |
| VBE_DISPI_INDEX_VIRT_WIDTH |
| VBE_DISPI_INDEX_VIRT_HEIGHT |
| VBE_DISPI_INDEX_X_OFFSET |
| VBE_DISPI_INDEX_Y_OFFSET |
| |
| 0xb0c2 supports 0xb0c1 VBE_DISPI_ interfaces, interfaces updated for |
| additional features (present in Bochs 2.1): |
| VBE_DISPI_INDEX_BPP supports >8bpp color depth (value = bits) |
| VBE_DISPI_INDEX_ENABLE supports new flags VBE_DISPI_NOCLEARMEM and VBE_DISPI_LFB_ENABLED |
| VBE i/o registers changed from 0xFF80/81 to 0x01CE/CF |
| |
| 0xb0c3 supports 0xb0c2 VBE_DISPI_ interfaces, interfaces updated for |
| additional features: |
| VBE_DISPI_INDEX_ENABLE supports new flags VBE_DISPI_GETCAPS and VBE_DISPI_8BIT_DAC |
| |
| 0xb0c4 VBE video memory increased to 8 MB |
| |
| |
| History |
| ------- |
| Version 0.6 2002 Nov 23 Jeroen Janssen |
| - Added LFB support |
| - Added Virt width, height and x,y offset |
| |
| Version 0.5 2002 March 08 Jeroen Janssen |
| - Added documentation about panic behaviour / current limits of the data values. |
| - Changed BPP API (in order to include future (A)RGB formats) |
| - Initial version (based upon extended display text of the vbe bochs display patch) |
| |
| |
| Todo |
| ---- |
| Version 0.6+ [random order] |
| - Add lots of different (A)RGB formats |
| |
| References |
| ---------- |
| [VBE3] VBE 3 Specification at |
| http://www.vesa.org/vbe3.pdf |
| |
| [BOCHS] Bochs Open Source IA-32 Emulator at |
| http://bochs.sourceforge.net |
| |
| [VBEBIOS] VBE Bios for Bochs at |
| http://savannah.gnu.org/projects/vgabios/ |
| |
| [Screenshots] Screenshots of programs using the VBE Bios at |
| http://japj.org/projects/bochs_plex86/screenshots.html |
| |
| Abbreviations |
| ------------- |
| VBE Vesa Bios Extension |
| DISPI (Bochs) Display Interface |
| BPP Bits Per Pixel |
| LFB Linear Frame Buffer |
| |
| |
| #defines |
| -------- |
| vbetables-gen.c |
| #define VBE_DISPI_TOTAL_VIDEO_MEMORY_MB 8 |
| |
| vbe.h |
| #define VBE_DISPI_BANK_ADDRESS 0xA0000 |
| #define VBE_DISPI_BANK_SIZE_KB 64 |
| |
| #define VBE_DISPI_MAX_XRES 1024 |
| #define VBE_DISPI_MAX_YRES 768 |
| |
| #define VBE_DISPI_IOPORT_INDEX 0x01CE |
| #define VBE_DISPI_IOPORT_DATA 0x01CF |
| |
| #define VBE_DISPI_INDEX_ID 0x0 |
| #define VBE_DISPI_INDEX_XRES 0x1 |
| #define VBE_DISPI_INDEX_YRES 0x2 |
| #define VBE_DISPI_INDEX_BPP 0x3 |
| #define VBE_DISPI_INDEX_ENABLE 0x4 |
| #define VBE_DISPI_INDEX_BANK 0x5 |
| #define VBE_DISPI_INDEX_VIRT_WIDTH 0x6 |
| #define VBE_DISPI_INDEX_VIRT_HEIGHT 0x7 |
| #define VBE_DISPI_INDEX_X_OFFSET 0x8 |
| #define VBE_DISPI_INDEX_Y_OFFSET 0x9 |
| |
| #define VBE_DISPI_ID0 0xB0C0 |
| #define VBE_DISPI_ID1 0xB0C1 |
| #define VBE_DISPI_ID2 0xB0C2 |
| #define VBE_DISPI_ID3 0xB0C3 |
| #define VBE_DISPI_ID4 0xB0C4 |
| |
| #define VBE_DISPI_DISABLED 0x00 |
| #define VBE_DISPI_ENABLED 0x01 |
| #define VBE_DISPI_VBE_ENABLED 0x40 |
| #define VBE_DISPI_NOCLEARMEM 0x80 |
| |
| #define VBE_DISPI_LFB_PHYSICAL_ADDRESS 0xE0000000 |
| |
| API |
| --- |
| The display api works by using a index (VBE_DISPI_IOPORT_INDEX) and |
| data (VBE_DISPI_IOPORT_DATA) ioport. One writes the index of the parameter to the index port. |
| Next, the parameter value can be read or written. |
| |
| [0xb0c0] |
| * VBE_DISPI_INDEX_ID : WORD {R,W} |
| This parameter can be used to detect the current display API (both bochs & vbebios). |
| The bios writes VBE_DISPI_ID0 to the dataport and reads it back again. |
| This way, the display code knows the vbebios 'ID' and the vbebios can check if the correct |
| display code is present. |
| As a result, a PANIC can be generated if an incompatible vbebios/display code combination is detected. |
| This panic can be generated from the bochs display code (NOT the bios, see Notes). |
| |
| Example values: VBE_DISPI_ID0 |
| |
| * VBE_DISPI_INDEX_XRES : WORD {R,W} |
| This parameter can be used to read/write the vbe display X resolution (in pixels). |
| It's illegal to set the XRES when the VBE is enabled (display code should generate PANIC). |
| |
| If the value written exceeds VBE_DISPI_MAX_XRES, the display code needs to generate a PANIC. |
| |
| Example values: 320,640,800,1024 |
| |
| * VBE_DISPI_INDEX_YRES : WORD {R,W} |
| This parameter can be used to read/write the vbe display Y resolution (in pixels). |
| It's illegal to set the YRES when the VBE is enabled (display code should generate PANIC). |
| |
| If the value written exceeds VBE_DISPI_MAX_YRES, the display code needs to generate a PANIC. |
| |
| Example values: 200,400,480,600,768 |
| |
| * VBE_DISPI_INDEX_BPP : WORD {R,W} |
| This parameter can be used to read/write the vbe display BPP. |
| It's illegal to set the BPP when the VBE is enabled (display code should generate PANIC). |
| |
| If the value written is an incompatible BPP, the display code needs to generate a PANIC. |
| |
| Example values: VBE_DISPI_BPP_8 |
| |
| * VBE_DISPI_INDEX_ENABLE : WORD {R,W} |
| This parameter can be used to read/write the vbe ENABLED state. |
| If the bios writes VBE_DISPI_ENABLED then the display code will setup a hostside display mode |
| with the current XRES, YRES and BPP settings. |
| If the bios write VBE_DISPI_DISABLED then the display code will switch back to normal vga mode behaviour. |
| |
| Example values: VBE_DISPI_ENABLED, VBE_DISPI_DISABLED |
| |
| * VBE_DISPI_INDEX_BANK : WORD {R,W} |
| This parameter can be used to read/write the current selected BANK (at 0xA0000). |
| This can be used for switching banks in banked mode. |
| |
| [0xb0c1] |
| * VBE_DISPI_INDEX_VIRT_WIDTH : WORD {R,W} |
| This parameter can be used to read/write the current virtual width. |
| Upon enabling a mode, this will be set to the current xres |
| Setting this field during enabled mode will result in the virtual width to be changed. |
| Value will be adjusted if current setting is not possible. |
| |
| * VBE_DISPI_INDEX_VIRT_HEIGHT : WORD {R} |
| This parameter can be read in order to obtain the current virtual height. |
| This setting will be adjusted after setting a virtual width in order to stay within limit of video memory. |
| |
| * VBE_DISPI_INDEX_X_OFFSET : WORD {R,W} |
| The current X offset (in pixels!) of the visible screen part. |
| Writing a new offset will also result in a complete screen refresh. |
| |
| * VBE_DISPI_INDEX_Y_OFFSET : WORD {R,W} |
| The current Y offset (in pixels!) of the visible screen part. |
| Writing a new offset will also result in a complete screen refresh. |
| |
| |
| [0xb0c2] |
| * VBE_DISPI_INDEX_BPP : WORD {R,W} |
| The value written is now the number of bits per pixel. A value of 0 is treated |
| the same as 8 for backward compatibilty. These values are supported: 8, 15, |
| 16, 24 and 32. The value of 4 is not yet handled in the VBE code. |
| * VBE_DISPI_INDEX_ENABLE : WORD {R,W} |
| The new flag VBE_DISPI_NOCLEARMEM allows to preserve the VBE video memory. |
| The new flag VBE_DISPI_LFB_ENABLED indicates the usage of the LFB. |
| |
| [0xb0c3] |
| * VBE_DISPI_INDEX_ENABLE : WORD {R,W} |
| If the new flag VBE_DISPI_GETCAPS is enabled, the xres, yres and bpp registers |
| return the gui capabilities. |
| The new flag VBE_DISPI_8BIT_DAC switches the DAC to 8 bit mode. |
| |
| [0xb0c4] |
| * VBE_DISPI_TOTAL_VIDEO_MEMORY_MB set to 8 (moved to auto-generated vbetables.h) |
| |
| Displaying GFX (banked mode) |
| -------------- |
| What happens is that the total screen is devided in banks of 'VBE_DISPI_BANK_SIZE_KB' KiloByte in size. |
| If you want to set a pixel you can calculate its bank by doing: |
| |
| offset = pixel_x + pixel_y * resolution_x; |
| bank = offset / 64 Kb (rounded 1.9999 -> 1) |
| |
| bank_pixel_pos = offset - bank * 64Kb |
| |
| Now you can set the current bank and put the pixel at VBE_DISPI_BANK_ADDRESS + bank_pixel_pos |
| |
| Displaying GFX (linear frame buffer mode) |
| -------------- |
| NOT WRITTEN YET |
| |
| Notes |
| ----- |
| * Since the XRES/YRES/BPP may not be written when VBE is enabled, if you want to switch from one VBE mode |
| to another, you will need to disable VBE first. |
| |
| * Note when the bios doesn't find a valid DISPI_ID, it can disable the VBE functions. This allows people to |
| use the same bios for both vbe enabled and disabled bochs executables. |
