>

 

  

 
Digression on r/w 00proc00

 files 

 
An application of kernel 

 module programming to Super VGA graphics device control

 

 

 

  

 
Super VGA   

 

 

   Modern graphics cards have 

   lots of vram

   Our class machines show only 

   part of it

   Screen resolution is 1280 

   x 1024 00ixels00

   Each 00ixel00is 32-bits 

   of video memory

   Total vram for one full screen:  

 

 
      1280 

 x 1024 x 4 bytes = 5 megabytes

 

   Our class machines have 32 

   megabytes

 

 

 

 

  

 
SVGA 00tart Address00

 parameter 

 

   Our machines use the SiS 315 

   svga chip

   Its 00tart Address00governs 

   what we see

   It00 a 24-bit value, held 

   in 3 byte-registers

   Registers accessible through 

   i/o ports

   Kernel code can reprogram 

   these registers

   Module-inferface gives application-access

 

 
 

 
 

 

 

 

  

 
How Start Address works 

 

 
VRAM 

 

 
visible 

 

 
Start_address = 0 

 
VRAM 

 

 
visible 

 

 
Start_address = 2048

 

 

 

  

 
The CRT Controller 

 

 

   Display monitor uses Cathode 

   Ray Tube

   It00 operated by SVGA00 

   CRT Controller 

   Old design: It has lots of 

   8-bit registers

   Two i/o port-addresses are 

   00ultiplrexed00/font>

   ADDRESS_PORT:  0x03D4

   DATA_PORT:   0x03D5

   CRTC register 13:  start_address[ 

   7..0 ]

   CRTC register 12:  start_address[ 

   15..8 ]

 

 

 

 

  

 
SVGA incompatibility 

 

 

   Many features of SVGA are 

   now standard

   But vendors add their own 

   00xtras00/font>

   These are NOT programmed identically!

   You usually need manufacturer00 

   manual

   But not always easy to get 

   (proprietary)

   (We found SiS information 

   in a web email)

   Software for SiS chip 00xtras00

   non-portable

 

 

 

 

  

 
SVGA Memory Sequencer 

 

 

   Sequencer also has lots of 

   8-bit registers

   They00e also accessed via 

   two i/o ports

   ADDRESS_PORT:  0x03C4

   DATA_PORT:   0x03C5

   Seq register 13:  start_address[ 

   23..16 ]

   SiS chip uses Seq register 

   5 as a 00ock00/font>

   Write 0x86 to 00nlock00

   sequencer registers 

 

 

 

 

  

 
pci_find_device() 

 

 

   Driver must 00etect00the 

   SiS SVGA device

   SiS chip00 VENDOR_ID is 

   0x1039

   SiS chip00 DEVICE_ID is 

   0x6325

 

  

 

   #include <linux/pci.h>

 

 
struct pci_dev  *devp = NULL;

 
devp = pci_find_device( VENDOR, DEVICE, 

 devp );

 

 

 

  

 
Class Demo 

 

 

   Module name is 00ischip.c00/font>

   Creates a pseudo-file: 00roc/sischip00/font>

   It00 a binary file (don00 

   use 00at00command)

   File is both readable and 

   writable

   Lets application get or set 

   00tart_address00/font>

   Our demo-program is 00gascroll.cpp00/font>

   It lets us see 16 megabytes 

   of video ram

 

 

 

 

  

 
Today00 Class Exercise 

 

 

   Use your knowledge of 00oremap()00/font>

   Draw an image in the offscreen 

   vram

   Run 00gascroll00to see 

   what you00e drawn