Patching svgalib Contents 0. Introduction 1. Indenting 2. Structure of the chipset drivers 0. Introduction Here is some info on writing patches and/or adding support for further chipsets. The info on the chipset drivers is outdated, but better than nothing and get you started. As a side note, other than a.out, ELF does not allow to have some symbols global to svgalib which are not accessible to user programs. Because of that, if possible all the symbols and functions in your program should be static. Those which can not be static should have a name like: "__svgalib_*" to mark them as internals s.t. people using them get what they deserve. Please do only add a new function to the user interface if it is really unavoidable. Better add some new parameters to an existing function. Adding a new function would definitly result in loosing a.out compatibility thus removing the chance to use new cards and such with old a.out binaries where the source is not available (doom comes to mind). A new function should be really important to outweigh this draw back. 1. Indenting Due to some request (and I heard it b4) all the sources were now automatically indentified. There were some requests for indent -gnu but it looks painful. I opted for -kr (there were requests for it as well) as it is not only nicer but also what is done in the linux-kernel and this is certainly a program only usable for linux. I dunno if emacs is confused by -kr, but to be honest this is a big all-in-one egg-giving-wool-milk-sow (as we say in german), and you won't tell me that this several megs beast is unable to edit this and I can't use -kr due to some restrictions of emacs. That would be really ridiculous. If it is the case just make emacs better. The OneModeEntry macro is eaten by indent (I would say it is an indent bug, I might send a bug report to them), please ensure (if at all possible) that your code can be passed through indent (use the INDENT-OFF comments as shown in some sources for OneModeEntry). You can use `make indent-gnu' (if you have a recent enough (I use 1.9.1) indent) to switch to your favorite style. But please ensure your patches fit into this now declared as "official style" sources. (Use `make indent' to reformat). Do not use it too often though as most indent's tend to add empty lines at certain places in the source. 2. Structure of the chipset drivers The chipset specific registers saving function (saveregs) is only used directly to save the textmode registers at initialization. The chipset specific registers restoring function (setregs) is only used directly to return to textmode, and when setting a VGA mode after an SVGA mode. The registers for each mode are stored like the ET4000 modes in VGAlib 1.2, i.e. the extended registers at the end. The following functions must be provided in a driver: saveregs( unsigned char regs[] ) Saves the chipset-specific registers in regs, starting at array index EXT (after the VGA registers). setregs( unsigned char regs[] ) Sets the chipset-specific registers stored in regs from index EXT. modeavailable( int mode ) Returns nonzero if mode is available (should check video memory). getmodeinfo( vga_modeinfo *modeinfo ) Fills in chipset specific field of mode information structure: maxlogicalwidth, startaddressrange (mask of significant bits), and maxpixels (video memory divided by the number of bytes per pixel). haveblit indicates whether bitblt functions are available. Note: providing extended info and an aperture with size >= memory and setting bits 4 and 6 in flags will automatically enable linear addressing support. setmode( int mode, int previous_mode ) Sets all registers for a mode; returns nonzero if mode not available. __vga_setregs can be called to set the VGA registers. unlock() Unlocks chipset-specific registers. lock() Lock (protect) chipset-specific registers. Currently not called. test() Identify chipset; initialize (check memory and type) and return nonzero if detected. setpage( int page ) Set 64K page number to be mapped at 0xa0000. init( int force, int par1, ... ) Initialize memory and type; called by test. If force is 1, the chiptype or the amount of memory can be forced (this is pretty useless). The following functions provide for things like page flipping and hardware scrolling virtual desktops. setdisplaystart( int address ) Sets the display start address in video memory in pixels. setlogicalwidth( int width ) Sets the logical scanline length in bytes. Usually a multiple of 8. The function getchipset() in vga.c must call the test routine for the chipset. The chipsetfunctionslist must be have a pointer to the chipsetfunctions table for the chipset (which is the only global symbol in a chipset driver). Also, vga.h contains a magic number for each chipset. Also driver_names[] in vga.c has to contain a name for each driver at the correct position.
