Manual browser: agp(4)

AGP(4) Kernel Interfaces Manual AGP(4)


agpaccelerated graphics port driver


agp* at pchb?


The agp driver provides machine-independent support for the accelerated graphics port (AGP) found on many PC-based and PCI systems. The AGP specification was designed by Intel.

The AGP chipset is positioned between the PCI-Host bridge and the graphics accelerator to provide a high-performance dedicated graphics bus for moving large amounts of data directly from host memory to the graphics accelerator. The specification currently supports a peak bandwidth of 528 MB/s. AGP uses a Graphics Address Remapping Table (GART) to provide a physically-contiguous view of scattered pages in host memory for DMA transfers.

The agp driver supports the following chipsets:

  • ALI M1541 host-to-AGP bridge
  • AMD 751 and 761 host-to-AGP bridges
  • Intel 82810, 82810-DC100, 82810E, and 82815 SVGA controllers
  • SiS 5591 host-to-AGP bridge
  • VIA

The agp driver also provides an interface to user processes for use by X servers. A user process communicates to the device initially by means of ioctl(2) calls. The calls supported are:

Get AGP information, setting the members in the agp_info structure as defined in <sys/agpio.h>:

typedef struct _agp_info { 
        agp_version version;    /* version of the driver        */ 
        uint32_t bridge_id;     /* bridge vendor/device         */ 
        uint32_t agp_mode;      /* mode info of bridge          */ 
        off_t aper_base;        /* base of aperture             */ 
        size_t aper_size;       /* size of aperture             */ 
        size_t pg_total;        /* max pages (swap + system)    */ 
        size_t pg_system;       /* max pages (system)           */ 
        size_t pg_used;         /* current pages used           */ 
} agp_info;
Acquire AGP.
Release AGP.
Set up AGP, using the members in the agp_setup structure as defined in <sys/agpio.h>:

typedef struct _agp_setup { 
        uint32_t agp_mode;      /* mode info of bridge          */ 
} agp_setup;
Allocate AGP space, using and setting the members in the agp_allocate structure as defined in <sys/agpio.h>:

typedef struct _agp_allocate { 
        int key;                /* tag of allocation            */ 
        size_t pg_count;        /* number of pages              */ 
        uint32_t type;          /* 0 == normal, other devspec   */ 
        uint32_t physical;      /* device specific (some devices 
                                 * need a phys address of the 
                                 * actual page behind the gatt 
                                 * table)                       */ 
} agp_allocate;
Deallocate AGP space.
Bind AGP space, using the members in the agp_bind structure as defined in <sys/agpio.h>:

typedef struct _agp_bind { 
        int key;                /* tag of allocation            */ 
        off_t pg_start;         /* starting page to populate    */ 
} agp_bind;
Unbind AGP space, using the members in the agp_unbind structure as defined in <sys/agpio.h>:

typedef struct _agp_unbind { 
        int key;                /* tag of allocation            */ 
        uint32_t priority;      /* priority for paging out      */ 
} agp_unbind;


AGP GART device special files
AGP GART device special file


This short code fragment is an example of opening the AGP device and performing some basic operations:

#include <sys/types.h> 
#include <sys/ioctl.h> 
#include <sys/agpio.h> 
#include <fcntl.h> 
#include <err.h> 
main(int argc, char **argv) 
	int fd; 
	agp_info info; 
	agp_allocate alloc; 
	agp_setup setup; 
	agp_bind bind; 
	agp_unbind unbind; 
	fd = open("/dev/agp0", O_RDWR); 
	if (fd < 0) 
		err(1, "open"); 
	if (ioctl(fd, AGPIOC_INFO, &info) < 0) 
		err(2, "ioctl AGPIOC_INFO"); 
	printf("version:	%u.%u\n", info.version.major, 
	printf("id:		%x\n", info.bridge_id); 
	printf("mode:		%x\n", info.agp_mode); 
	printf("base:		%x\n", info.aper_base); 
	printf("size:		%uM\n", info.aper_size); 
	printf("total mem:	%u\n", info.pg_total); 
	printf("system mem:	%u\n", info.pg_system); 
	printf("used mem:	%u\n\n", info.pg_used); 
	setup.agp_mode = info.agp_mode; 
	if (ioctl(fd, AGPIOC_SETUP, &setup) < 0) 
		err(3, "ioctl AGPIOC_SETUP"); 
	if (ioctl(fd, AGPIOC_ACQUIRE, 0) < 0) 
		err(3, "ioctl AGPIOC_ACQUIRE"); 
	alloc.type = 0; 
	alloc.pg_count = 64; 
	if (ioctl(fd, AGPIOC_ALLOCATE, &alloc) < 0) 
		err(4, "ioctl AGPIOC_ALLOCATE"); 
	printf("alloc key %d, paddr %x\n", alloc.key, alloc.physical); 
	if (ioctl(fd, AGPIOC_INFO, &info) < 0) 
		err(5, "ioctl AGPIOC_INFO"); 
	bind.key = alloc.key; 
	bind.pg_start = 0x1000; 
	if (ioctl(fd, AGPIOC_BIND, &bind) < 0) 
		err(6, "ioctl AGPIOC_BIND"); 
	printf("used mem now:	%u\n\n", info.pg_used); 
	unbind.key = alloc.key; 
	unbind.priority = 0; 
	if (ioctl(fd, AGPIOC_UNBIND, &unbind) < 0) 
		err(6, "ioctl AGPIOC_BIND"); 
	if (ioctl(fd, AGPIOC_DEALLOCATE, &alloc.key) < 0) 
		err(6, "ioctl AGPIOC_DEALLOCATE"); 
	if (ioctl(fd, AGPIOC_RELEASE, 0) < 0) 
		err(7, "ioctl AGPIOC_RELEASE"); 
	printf("agp test successful\n"); 
	return 0; 


ioctl(2), pci(4)


The agp driver first appeared in FreeBSD 4.1. It was adopted in NetBSD 1.6.
October 3, 2010 NetBSD 7.0