Notes for Lab 10
On implementing ‘show’ and ‘hide’
for the SiS 315 hardware cursor
The GPU resources
• The SiS 315 graphics processing units in
our workstations are each equipped with
32-megabytes of video display memory
(designated as PCI resource 0)
• These graphics adapters also implement a
set of memory-mapped registers known as
the 2D graphics engine (and designated
as PCI resource 1)
‘pci_resource_start()’
• Device-drivers can use this Linux kernel
function to discover the physical address
where resource 0, or resource 1, resides
struct pci_dev *devp = NULL:
devp = pci_find_device( VEN, DEV, devp );
vram = pci_resource_start( devp, 0 );
mmio = pci_resource_start( devp, 1 );
SiS 315 information
• Programming manual for the SiS 315 GPU
is not usually made available to the public
• But some information can be derived from
reading Linux device-driver source-code
• Examples are:
– The ‘/usr/src/linux/drivers/video/sis’ directory
– Also download the ‘svgalib-1.9.17’ package
Graphics Cursor
31 30
0x8500
0
cursor-image source-offset
cursor visibility control bit: 0=hide, 1=show
cursor starting command bit: 0=no, 1=yes
0x850C
cursor-image horizontal coordinate
0x8510
cursor-image vertical coordinate
Algorithm to hide cursor
• Map physical page containing the registers
to a virtual address (with ‘ioremap()’)
• Read current values of these registers
• Clear bit #30 (to make cursor invisible)
• Set bit #31 (to initiate a new command)
• Write these adjusted register values
• Undo the mapping (with ‘iounmap()’)
Algorithm to show cursor
• Map physical page containing the registers
to a virtual address (with ‘ioremap()’)
• Read current values of these registers
• Set bit #30 (to make cursor visible)
• Set bit #31 (to initiate a new command)
• Write these adjusted register values
• Undo the mapping (with ‘iounmap()’)
The ‘ioctl.c’ module
• These techniques are demonstrated in this
device-driver module’s ‘ioctl()’ function
• Two IOCTL commands are implemented
– #define CURSOR_HIDE
– #define CURSOR_SHOW
0
1
• Applications can open the device-file, then
use an ioctl-command; for example:
int fd = open( “/dev/vram”, O_RDWR );
ioctl( fd, CURSOR_HIDE);
In-class exercise:
• Try adding new IOCTL commands to the
‘ioctl.c’ driver which lets applications find
or move the cursor’s screen-position;
#define CURSOR_FIND
2
#define CURSOR_MOVE 3
struct { long x, y; } location;
ioctl( fd, CURSOR_FIND, &location );
location.x += 40; location.y += 40;
ioctl( fd, CURSOR_MOVE, &location );