SiS 315 Graphics Engine Introduction to some capabilities of graphics accelerator hardware SVGA incompatibilities SVGA manufacturers have different ways of implementing their accelerator features SiS provides 2D and 3D graphics engines Access is via memory mapped i o ports This requires a new Linux device driver to allow mapping the io ports into user space A suitable driver is our engine2d c It only works with SiS graphics hardware SiS policy SiS officials say it is not company policy to provide individuals with programming info But some programming info is available in unofficial sources e g in line comments by programmers who wrote open source device drivers for Linux XFree86 systems Not everything is fully explained though So a lot of trial and error is necessary Where to look for info The source code for drivers distributed with the Linux kernel can be found in usr src local linux drivers video sis Recent versions of the SVGALIB package have some SiS specific code you can view There is also a website maintained by the author of the SiS driver for Linux Thomas Winischhofer http www winischhofer net Linux kernel modules Linux permits installing new kernel code at runtime i e without recompiling kernel A system administrator can install remove kernel modules and may grant users this same privilege by adjusting permissions on the insmod and rmmod commands Modules are written in the C language not C and include special header files that are distributed with the kernel source code Module requirements Must define KERNEL and MODULE before any include statements Must have include linux module h Maybe others e g include linux pci h Must have these two public functions int init module void void cleanup module void Usually device specific function s too Driver Module Structure filename and module abstract include define typedef static data objects read write lseek mmap This is the device driver core struct file operations init module cleanup module MODULE LICENSE These are for module mgmt Our engine2d c module Our module only needs one extra function int my mmap Also needs a struct file operations object struct file operations my fops The init module function will install that structure object in kernel space together with executable code which it references The cleanup module function removes that code and data after we re finished How it works user space kernel space int 0x80 runtime library iret syscall handler ret mmap application program call ret device driver module Pentium s Page Tables Our driver s mmap method calls a kernel procedure that knows how to setup some new entries in the CPU s page directory and page table data structures which give the effect of mapping the GPU s i o ports into an application s virtual address space Then the program can read or write these i o ports as if they were memory locations The PCI Interface The graphics hardware connects with the CPU using the AGP bus conforming to a standard PCI bus programming interface Linux kernel functions can be called from our init module to query the GPU chip Identify the chip s make and model Get physical address for its i o memory Determine the length of the i o memory Linux device nodes Linux treats devices as if they were files We must create a device file for our GPU Device files normally go in dev directory We invent a filename for our device file We pick an unused device id number A system administrator creates the file root mknod dev sismmio c 101 0 root chmod a rw dev sismmio Our sisaccel cpp demo We have written a short demo program It uses the SiS 315 s 2D graphics engine It fills some rectangles with a solid color It also shows how to draw a line segment These operations could be done as we know with software algorithms but it s faster to let the hardware do it instead You are invited to experiment further include sisaccel h This header defines symbolic names for some of the 2D engine s i o addresses Accelerator commands involve writing the values for various parameters to these i o port addresses concluding with a value that encodes a desired engine command Some Extended Sequencer registers must be initialized beforehand to enable engine Truecolor Graphics We used VESA graphics mode 0x413B Screen resolution is 800x600 Pixels are 32 bits in size Truecolor Recall the Truecolor pixel format byte3 Alpha channel byte2 byte1 byte0 Makefile In order to compile the engine2d c driver we recommend using the Makefile on our class website copy it to your directory make engine2d o Be sure you compile it BEFORE you try to run the gpuaccel cpp demo program Don t forget that your IOPL needs to be 3 e g run the iopl3 program first
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