ARCH(3)						       ARCH(3)

     NAME
	  arch - architecture-specific information and control

     SYNOPSIS
	  bind -a #P /dev
	  /dev/acpitbls
	  /dev/archctl
	  /dev/cputype
	  /dev/cputemp
	  /dev/ec
	  /dev/ioalloc
	  /dev/iob
	  /dev/iol
	  /dev/iow
	  /dev/irqalloc
	  /dev/msr
	  /dev/realmodemem

     DESCRIPTION
	  This device presents textual information about PC hardware
	  and allows user-level	control	of the I/O ports on x86-class
	  machines.

	  Reads	from cputemp return the	current	temperature reported
	  by the CPU, one line per core.  Each line contains two
	  integers separated by	a ± character,	the reading and	its
	  resolution, both in degrees Celsius.	An `alarm' status
	  string preceded by a space character may be appended to the
	  line in case critical	temperature levels are detected.

	  Reads	from cputype recover the processor type	and clock rate
	  in MHz.  Reads from archctl yield at least data of this
	  form:

	       cpu AMD64 2201 pge
	       pge on
	       coherence mfence
	       cmpswap cmpswap486
	       i8253set	on
	       cache default uc
	       cache 0x0 1073741824 wb
	       cache 0x3ff00000	1048576	uc

	  Where	`AMD64'	is the processor type, `2201' is the processor
	  speed	in MHz,	and `pge' is present only if the `page global
	  extension' capability	is present; the	next line reflects its
	  setting.  `coherence'	is followed by one of `mb386',
	  `mb586', `mfence' or `nop', showing the form of memory bar-
	  rier used by the kernel.  `cmpswap' is followed by
	  `cmpswap386' or `cmpswap486',	reflecting the form of `com-
	  pare and swap' used by the kernel.  `i8253set' is a flag,
	  indicating the need to explicitly set	the Intel 8253 or
	  equivalent timer.  There may be lines	starting with `cache'
	  that reflect the state of memory caching via MTRRs (memory-
	  type region registers).  The second word on the line is
	  `default' or a C-style number	which is the base physical
	  address of the region; the third is a	C-style	length of the
	  region; and the fourth is one	of `uc'	(for uncachable), `wb'
	  (write-back),	`wc' (write-combining),	`wp' (write-
	  protected), or `wt' (write-through).	A region may be	a sub-
	  set of another region, and the smaller region	takes pre-
	  cedence.  This may be	used to	make I/O registers uncachable
	  in the midst of a write-combining region mostly used for a
	  video	framebuffer, for example.  Control messages may	be
	  written to archctl and use the same syntax as	the data read
	  from archctl.	Known commands include `cache',	`coherence',
	  `i8253set', and `pge'.

	  Reads	from ioalloc return I/O	ranges used by each device,
	  one line per range.  Each line contains three	fields
	  separated by white space: first address in hexadecimal, last
	  address, name	of device.

	  Reads	from irqalloc return the enabled interrupts, one line
	  per interrupt.  Each line contains five fields separated by
	  white	space: the trap	number,	the IRQ	it is assigned to, the
	  handling cpu number, device location
	  (type.bus.device.function) and the name of the device	using
	  it.

	  Reads	and writes to iob, iow,	and iol	cause 8-bit wide, 16-
	  bit wide, and	32-bit wide requests to	I/O ports.  The	port
	  accessed is determined by the	byte offset of the file
	  descriptor.

	  Reads	and writes to msr go to	the P4/P6/Core/Core2/AMD64
	  MSRs.

	  The realmodemem file provides	access to the first megabyte
	  of memory. This allows reading BIOS data structures and
	  option ROMs.	Writing	is limited to the VGA framebuffer at
	  [0xA0000-0xBFFFF].

	  Reads	and writes to ec transfer bytes	from and to the	embed-
	  ded controller.

	  Reads	from acpitbls return a concatenation of	system ACPI
	  tables. Each table is	prefixed with a	fixed size header that
	  gives	the name signature and size of the table (see section
	  5.2.6	System Description Table Header	in the ACPI specifica-
	  tion).

     EXAMPLE
	  The following	code reads from	an x86 byte I/O	port.

	       uchar
	       inportb(unsigned	port)
	       {
		   uchar data;

		   if(iobfd == -1)
		       iobfd = open("#P/iob", ORDWR);

		   seek(iobfd, port, 0);
		   if(read(iobfd, &data, sizeof(data)) != sizeof(data))
		       sysfatal("inportb(0x%4.4ux): %r", port);
		   return data;
	       }

     SOURCE
	  /sys/src/9/pc/devarch.c