ARCH(3) ARCH(3)
NAME
arch - 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 `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 prece-
dence. This may be used to make I/O registers uncachable in
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ARCH(3) ARCH(3)
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 sepa-
rated 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 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
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