SCSI(4) SCSI(4)
NAME
scsi - SCSI interface
SYNOPSIS
#include <scsi.h>
DESCRIPTION
The special file provides a low level interface to a SCSI
bus. Commands are transmitted to the bus by write; the
response to each command is received with read(2). The for-
mat of a command is
unsigned long tran_id; /* transaction id */
unsigned char target; /* SCSI id of target device */
unsigned char flags; /* flags for this transaction */
unsigned long nreturn; /* number of bytes to be read back */
char cmd[10]; /* SCSI command */
char data[]; /* optional data */
Thus, to send n bytes of data, the byte count for write
should be n+20. Possible flags are SCSI_WR (data goes from
host to SCSI), SCSI_RD (data goes from SCSI to host),
SCSI_BRESET (reset the SCSI bus), SCSI_RESET (reset the con-
troller), and SCSI_SENSE (return extended sense data on
error). For most controllers, SCSI_BRESET implies
SCSI_RESET. Flags are OR'ed together, and there must be
exactly one of SCSI_WR and SCSI_RD. The SCSI command should
terminate within a small time (currently 10 seconds); a
longer limit (300 seconds) can be specified by using
SCSI_LTMOUT.
The data read is structured as
unsigned long tran_id; /* transaction id */
unsigned char status; /* scsi status byte */
unsigned char message; /* scsi message byte */
unsigned char flags; /* flags for this transaction */
unsigned char c_type; /* 1=td 2=us */
unsigned short c_reg1; /* td=sa, us=csr */
unsigned short c_reg2; /* td=mscp, us=per */
unsigned char sense[22]; /* extended sense data */
char pad[2];
char data[]; /* any data */
Thus, to read n bytes of data. the byte count to read should
be n+36. If flags has the SCSI_CERR bit set, there was a
controller error, which is described by the c_ fields. The
values of csr (or sa) and per (or mscp) are documented in
the interface manual for the U.S. Design 1158 Unibus con-
troller (or T.D. Systems Viking controller). If the
SCSI(4) SCSI(4)
SCSI_SENSE bit was set in the write, and the status byte
shows a check condition, an attempt is made to get extended
sense information. If the attempt succeeds the SCSI_SENSE
is set in flags. Otherwise, the status and message bytes for
the failed attempt are placed in sense[0] and sense[1]
respectively.
The transaction id identifies which write caused the results
for this read. This will become more important when multiple
simultaneous transactions are allowed.
FILES
SEE ALSO
scsish(8)