SiS 315 Graphics Engine

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/linu
  x/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

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 ltlinux/module.hgt
• Maybe others e.g., include ltlinux/pci.hgt
• Must have these two public functions int
  init_module( void ) void cleanup_module( void
  )
• Usually device-specific function(s), too

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

9
How it works
kernel-space
user-space
int 0x80
runtime library
syscall handler
iret
ret
call
mmap
ret
application program
device-driver module
10
Pentiums Page-Tables

• Our drivers mmap method calls a kernel
  procedure that knows how to setup some new
  entries in the CPUs page-directory and
  page-table data-structures which give the effect
  of mapping the GPUs i/o-ports into an
  applications 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 chips 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 arw
  /dev/sismmio

13
Our sisaccel.cpp demo

• We have written a short demo-program
• It uses the SiS 315s 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 its 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 engines 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

byte2
byte1
byte0
byte3
Alpha channel
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
• Dont forget that your IOPL needs to be 3 e.g.,
  run the iopl3 program first