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SiS 315 Graphics Engine Introduction to some capabilities of graphics accelerator hardware.

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Presentation on theme: "SiS 315 Graphics Engine Introduction to some capabilities of graphics accelerator hardware."— Presentation transcript:

1 SiS 315 Graphics Engine Introduction to some capabilities of graphics accelerator hardware

2 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

3 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!

4 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):

5 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

6 Module requirements Must define __KERNEL__ and MODULE before any #include statements Must have: #include Maybe others: e.g., #include Must have these two public functions: int init_module( void ); void cleanup_module( void ); Usually device-specific function(s), too

7 Driver-Module Structure init_module() cleanup_module() MODULE_LICENSE struct file_operations write() lseek() mmap() read() static data objects #define ----------- #include --------- typedef ------------- // filename and module abstract This is the device-driver core These are for module mgmt

8 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

9 How it works kernel-spaceuser-space application program runtime library syscall handler device-driver module int $0x80 iret mmap ret call ret

10 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

11 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

12 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

13 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!

14 #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

15 Truecolor Graphics We used VESA graphics mode 0x413B Screen-resolution is 800x600 Pixels are 32-bits in size (‘Truecolor’) Recall the Truecolor pixel-format: Alpha channel byte0byte3 byte2byte1

16 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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