.\"	$OpenBSD: rx.4,v 1.11 2007/05/31 19:19:57 jmc Exp $
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.\"     from: @(#)rx.4	6.2 (Berkeley) 3/27/91
.\"
.Dd $Mdocdate: May 31 2007 $
.Dt RX 4 vax
.Os
.Sh NAME
.Nm rx
.Nd
.Tn DEC
.Tn RX02
floppy disk interface
.Sh SYNOPSIS
.Cd "rx* at mscpbus? drive?"
.Sh DESCRIPTION
The
.Nm rx
device provides access to a
.Tn DEC
.Tn RX02
floppy disk
unit with M8256 interface module
.Pf ( Tn RX211
configuration).
The
.Tn RX02
uses 8-inch, single-sided, soft-sectored floppy
disks (with pre-formatted industry-standard headers) in
either single or double density.
.Pp
Floppy disks handled by the
.Tn RX02
contain 77 tracks, each with 26
sectors (for a total of 2,002 sectors).
The sector size is 128 bytes for single density, 256 bytes for double density.
Single density disks are compatible with the
.Tn RX01
floppy disk unit and with
.Tn IBM
3740 Series Diskette 1 systems.
.Pp
In addition to normal (`block' and `raw')
.Tn I/O ,
the driver supports
formatting of disks for either density and
the ability to invoke a 2 for 1 interleaved sector mapping
compatible with the
.Tn DEC
operating system
.Tn RT-11 .
.Pp
The minor device number is interpreted as follows:
.Bl -column Otherx -offset indent
.Sy Bit	Description
0	Sector interleaving  (1 disables interleaving)
1	Logical sector 1 is on track 1 (0 no, 1 yes)
2	Not used, reserved
Other	Drive number
.El
.Pp
The two drives in a single
.Tn RX02
unit are treated as
two disks attached to a single controller.
Thus, if there are two
.Tn RX02 Ns 's
on a system, the drives on the first
.Tn RX02
are
.Dq Li rx0
and
.Dq Li rx1 ,
while the drives on the second are
.Dq Li rx2
and
.Dq Li rx3 .
.Pp
When the device is opened, the density of the disk
currently in the drive is automatically determined.
If there is no floppy in the device, open will fail.
.Pp
The interleaving parameters are represented in raw device
names by the letters
.Ql a
through
.Ql d .
Thus, unit 0, drive 0 is
called by one of the following names:
.Bl -column interleavedxx "Device namexx" "Starting Track" -offset indent
.Sy Mapping	Device name	Starting track
interleaved	/dev/rrx0a	0
direct	/dev/rrx0b	0
interleaved	/dev/rrx0c	1
direct	/dev/rrx0d	1
.El
.Pp
The mapping used on the
.Ql c
device is compatible with the
.Tn DEC
operating system
.Tn RT-11 .
The
.Ql b
device accesses the
sectors of the disk in strictly sequential order.
The
.Ql a
device is the most efficient for disk-to-disk copying.
This mapping is always used by the block device.
.Pp
.Tn I/O
requests must start on a sector boundary, involve an integral
number of complete sectors, and not go off the end of the disk.
.Sh NOTES
Even though the storage capacity on a floppy disk is quite
small, it is possible to make filesystems on
double density disks.
For example, the command
.Bd -literal -offset indent
% mkfs /dev/rx0 1001 13 1 4096 512 32 0 4
.Ed
.Pp
makes a file system on the double density disk in rx0 with
436 kbytes available for file storage.
Using
.Xr tar 1
gives a more efficient utilization of the available
space for file storage.
Single density diskettes do not provide sufficient storage capacity to
hold file systems.
.Pp
A number of
.Xr ioctl 2
calls apply to the rx devices:
.Bl -tag -width RXIOC_GETDENS
.It Dv RXIOC_FORMAT
Format the diskette.
The density to use is specified by the
.Ar arg
argument, zero gives single density while non-zero
gives double density.
.It Dv RXIOC_GETDENS
Return the density of the diskette (zero or non-zero as above).
.It Dv RXIOC_WDDMK
On the next write, include a
.Em deleted data address mark
in
the header of the first sector.
.It Dv RXIOC_RDDMK
Return non-zero if the last sector read contained a
.Em deleted data address mark
in its header, otherwise
return 0.
.El
.Sh FILES
.Bl -tag -width /dev/rx?xx -compact
.It Pa /dev/rx?
.It Pa /dev/rrx?[a-d]
.El
.Sh DIAGNOSTICS
.Bl -diag
.It "rx%d: hard error, trk %d psec %d cs=%b, db=%b, err=%x, %x, %x, %x."
An unrecoverable error was encountered.
The track and physical sector numbers, the device registers and the
extended error status are displayed.
.Pp
.It rx%d: state %d (reset).
The driver entered a bogus state.
This should not happen.
.El
.Sh ERRORS
The following errors may be returned by the driver:
.Bl -tag -width [ENODEV]
.It Bq Er ENODEV
Drive not ready; usually because no disk is in the drive or
the drive door is open.
.It Bq Er ENXIO
Nonexistent drive (on open);
offset is too large or not on a sector boundary or
byte count is not a multiple of the sector size (on read or write);
or bad (undefined) ioctl code.
.It Bq Er EIO
A physical error other than ``not ready'', probably bad media or
unknown format.
.It Bq Er EBUSY
Drive has been opened for exclusive access.
.It Bq Er EBADF
No write access (on format), or wrong density; the latter
can only happen if the disk is changed without
.Em closing
the device
(i.e., calling
.Xr close 2 ) .
.El
.Sh SEE ALSO
.Xr intro 4 ,
.Xr mscpbus 4 ,
.\" .Xr arff 8 ,
.Xr mkfs 8 ,
.Xr newfs 8
.\" .Xr rxformat 8
.Sh HISTORY
The
.Nm
driver appeared in
.Bx 4.2 .
.Sh BUGS
A floppy may not be formatted if the
header info on sector 1, track 0 has been damaged.
Hence, it is not possible to format completely degaussed disks or disks with
other formats than the two known by the hardware.
.Pp
If the drive subsystem is powered down when the machine is booted, the
controller won't interrupt.