.TH SCSI 3 
.SH NAME
scsi \- SCSI command interface
.SH SYNOPSIS
.nf
.B #S/id
.B #S/0/cmd
.B #S/0/data
.B #S/0/debug
\&...
.fi
.SH DESCRIPTION
.PP
The
.I scsi
interface is accessed through a two-level directory.
The single-byte
.B id
file contains the
.SM SCSI
id of the host interface, typically 7.
Some implementations allow this to be changed by writing to the file;
in many cases, the higher-order bits are hardware specific.
.PP
Each
.SM SCSI
target
.I n
.if n .RI "(0<=" n "<=7)"
.if t .RI "(0\(<=" n "\(<=7)"
is associated with a subdirectory
.BI "#S/" n
containing files
.BR cmd ,
.BR data ,
and
.BR debug .
The following steps may be used to execute a
.SM SCSI
command:
.IP
The command block is written to the
.B cmd
file.
.IP
The
.B data
file is either written or read depending on
the direction of the transfer.  (A command that involves no data transfer
is executed with a zero-length write.)
.IP
The
.B cmd
file is read to retrieve the status of the command,
returned as a 4-byte big-endian integer.
.PP
Writing an
.SM ASCII
.L 1
to the
.B debug
file causes tracing information to be written to
.BR /dev/klog ;
writing a
.L 0
turns the tracing off.
.PP
.SH SEE ALSO
.IR hard (3)