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DEVICE.HINTS(5)		      File Formats Manual	       DEVICE.HINTS(5)

NAME
       device.hints -- device resource hints

DESCRIPTION
       The  device.hints file is read in by the	boot loader(8) when the	system
       is about	to start, and its contents are passed to the kernel.  It  con-
       tains  various  variables  to  control the boot behavior	of the kernel.
       These variables are typically "device hints", but can include any  ker-
       nel tunable values.

       The  file  contains one variable	per line.  Lines starting with the `#'
       character are comments and are ignored by the boot loader.

       After the file is read by the boot loader, you may  examine  the	 vari-
       ables  with the show command, and may add a new variable, modify	an ex-
       isting one, or delete a variable	with the set and unset commands	of the
       boot loader (see	loader(8)).

       After the system	has started, you can dump  these  variables  with  the
       kenv(1) command.

DEVICE HINTS
       Device  hint variables are used by device drivers to set	up the device.
       They are	most often used	by ISA device drivers  to  specify  where  the
       driver  will probe for the relevant devices, and	what resources it will
       attempt to use.

       A device	hint line looks	like:

	     hint.driver.unit.keyword="value"

       where driver is the name	of a device driver, unit is the	 unit  number,
       and keyword is the keyword of the hint.	The keyword may	be:

	     at	       specifies a bus to which	the device is attached.
	     port      specifies  the start address of I/O ports to be used by
		       the device.
	     portsize  specifies the number of ports used by the device.
	     irq       is the interrupt	line number to be used.
	     drq       is the DMA channel number.
	     maddr     specifies the physical memory address used by  the  de-
		       vice.
	     msize     specifies the physical memory size used by the device.
	     flags     sets various flag bits for the device.
	     disabled  can be set to "1" to disable the	device.

       A device	driver may require one or more hint lines with these keywords,
       and    may   accept   other   keywords	not   listed   here,   through
       resource_int_value(9).  Consult individual device drivers' manual pages
       for available keywords and their	possible values.

FILES
       /boot/device.hints	     Device resource hints file.
       /sys/ARCH/conf/GENERIC.hints  Sample resource  hints  for  the  GENERIC
				     kernel.
       /sys/ARCH/conf/NOTES	     Notes  on	the  kernel configuration file
				     and device	resource hints.

EXAMPLES
       The following example sets up resources for the uart(4) driver  on  the
       ISA bus:

	     hint.uart.0.at="isa"
	     hint.uart.0.port="0x3F8"
	     hint.uart.0.flags="0x10"
	     hint.uart.0.irq="4"

       The following example disables the ACPI driver:

	     hint.acpi.0.disabled="1"

       Setting a tunable variable:

	     vm.pmap.pg_ps_enabled=1

SEE ALSO
       kenv(1),	loader.conf(5),	loader(8), resource_int_value(9)

HISTORY
       The device.hints	file first appeared in FreeBSD 5.0.

FreeBSD	14.3		       November	19, 2019	       DEVICE.HINTS(5)

Want to link to this manual page? Use this URL:
<https://man.freebsd.org/cgi/man.cgi?query=device.hints&manpath=FreeBSD+14.3-RELEASE+and+Ports>

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