ARCH(3)ARCH(3)NAMEarch - architecture-specific information and control
SYNOPSIS
bind -a #P /dev
/dev/archctl
/dev/cputype
/dev/ioalloc
/dev/iob
/dev/iol
/dev/iow
/dev/irqalloc
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 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 is the processor type, is the processor speed in MHz, and is
present only if the `page global extension' capability is present; the
next line reflects its setting. is followed by one of or showing the
form of memory barrier used by the kernel. is followed by or reflect‐
ing the form of `compare and swap' used by the kernel. is a flag,
indicating the need to explicitly set the Intel 8253 or equivalent
timer. There may be lines starting with that reflect the state of mem‐
ory caching via MTRRs (memory-type region registers). The second word
on the line is 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 (for uncachable), (write-back), (write-combining),
(write-protected), or (write-through). A region may be a subset of
another region, and the smaller region takes precedence. 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 mes‐
sages may be written to archctl and use the same syntax as the data
read from archctl. Known commands include and
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 inter‐
rupt. Each line contains three fields separated by white space: the
trap number, the IRQ it is assigned to, 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.
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
ARCH(3)
