.TH ARCH 3
.SH NAME
arch \- architecture-specific information and control
.SH SYNOPSIS
.nf
.B bind -a #P /dev

.B /dev/cputype
.B /dev/ioalloc
.B /dev/iob
.B /dev/iol
.B /dev/iow
.B /dev/irqalloc
.SH DESCRIPTION
.PP
This device presents textual information about PC hardware and allows
user-level control of the I/O ports on x86-class and DEC Alpha machines.
.PP
Reads from
.I cputype
recover the processor type and clock rate.
.PP
Reads from
.I 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.
.PP
Reads from
.I 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.
.PP
Reads and writes to
.IR iob ,
.IR iow ,
and
.I 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.
.SH EXAMPLE
The following code reads from an x86 byte I/O port.
.IP
.EX
uchar
inportb(long 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%4.4x): %r\en", port);
    return data;
}
.EE
.SH SOURCE
.B /sys/src/9/pc/devarch.c