Digression on r/w ‘/proc’ 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 ‘pixels’ Each ‘pixel’ is 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 ‘Start Address’ parameter Our machines use the SiS 315 svga chip Its ‘Start Address’ governs what we see It’s 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 It’s operated by SVGA’s CRT Controller Old design: It has lots of 8-bit registers Two i/o port-addresses are ‘multiplrexed’ ADDRESS_PORT: 0x03D4 DATA_PORT: 0x03D5 CRTC register 13: start_address[ 7..0 ] CRTC register 12: start_address[ ]

SVGA incompatibility Many features of SVGA are now standard But vendors add their own ‘extras’ These are NOT programmed identically! You usually need manufacturer’s manual But not always easy to get (proprietary) (We found SiS information in a web ) Software for SiS chip ‘extras’ non-portable

SVGA Memory Sequencer Sequencer also has lots of 8-bit registers They’re also accessed via two i/o ports ADDRESS_PORT: 0x03C4 DATA_PORT: 0x03C5 Seq register 13: start_address[ ] SiS chip uses Seq register 5 as a ‘lock’ Write 0x86 to ‘unlock’ sequencer registers

pci_find_device() Driver must ‘detect’ the SiS SVGA device SiS chip’s VENDOR_ID is 0x1039 SiS chip’s DEVICE_ID is 0x6325 #include struct pci_dev *devp = NULL; devp = pci_find_device( VENDOR, DEVICE, devp );

Class Demo Module name is ‘sischip.c’ Creates a pseudo-file: ‘proc/sischip’ It’s a binary file (don’t use ‘cat’ command) File is both readable and writable Lets application get or set ‘start_address’ Our demo-program is ‘vgascroll.cpp’ It lets us see 16 megabytes of video ram

Today’s Class Exercise Use your knowledge of ‘ioremap()’ Draw an image in the offscreen vram Run ‘vgascroll’ to see what you’ve drawn