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Implementing 'show' and 'hide' for SiS 315 hardware cursor

Learn how to implement 'show' and 'hide' functionality for the SiS 315 hardware cursor using Linux device-driver source code and ioctl commands.

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Implementing 'show' and 'hide' for SiS 315 hardware cursor

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  1. Notes for Lab 10 On implementing ‘show’ and ‘hide’ for the SiS 315 hardware cursor

  2. 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)

  3. ‘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 );

  4. 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

  5. Graphics Cursor 31 30 0 cursor-image source-offset 0x8500 cursor visibility control bit: 0=hide, 1=show cursor starting command bit: 0=no, 1=yes cursor-image horizontal coordinate 0x850C cursor-image vertical coordinate 0x8510

  6. 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()’)

  7. 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()’)

  8. The ‘ioctl.c’ module • These techniques are demonstrated in this device-driver module’s ‘ioctl()’ function • Two IOCTL commands are implemented • #define CURSOR_HIDE 0 • #define CURSOR_SHOW 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);

  9. 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 );

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