RX(4)

NAME
rx - DEC RX02 floppy disk interface

SYNOPSIS
controller fx0 at uba0 csr 0177170 vector rxintr
disk rx0 at fx0 drive 0
disk rx1 at fx0 drive 1

DESCRIPTION
The rx device provides access to a DEC RX02 floppy disk unit with M8256 interface module (RX211 configuration). The RX02 uses 8-inch, single-sided, soft-sectored floppy disks (with pre-formatted industry-standard headers) in either single or double density.

Floppy disks handled by the 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 RX01 floppy disk unit and with IBM 3740 Series Diskette 1 systems.

In addition to normal (`block' and `raw') 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 DEC operating system RT-11.

The minor device number is interpreted as follows:

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

The two drives in a single RX02 unit are treated as two disks attached to a single controller. Thus, if there are two RX02's on a system, the drives on the first RX02 are “rx0” and “rx1”, while the drives on the second are “rx2” and “rx3”.

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.

The interleaving parameters are represented in raw device names by the letters ‘a’ through ‘d’. Thus, unit 0, drive 0 is called by one of the following names:

Mapping Device name Starting track interleaved /dev/rrx0a 0 direct /dev/rrx0b 0 interleaved /dev/rrx0c 1 direct /dev/rrx0d 1

The mapping used on the ‘c’ device is compatible with the DEC operating system RT-11. The ‘b’ device accesses the sectors of the disk in strictly sequential order. The ‘a’ device is the most efficient for disk-to-disk copying. This mapping is always used by the block device.

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.

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

    % newfs -s 1001 -u 13 -t 1 -b 4096 -f 512 -c 32 -m 0 -r 240 /dev/rx0

makes a file system on the double density disk in rx0 with 436 kbytes available for file storage. Using 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.

A number of ioctl(2) calls apply to the rx devices, and have the form

    #include <vaxuba/rxreg.h>
    ioctl(fildes, code, arg)
    int *arg;

The applicable codes are:

RXIOC_FORMAT
    Format the diskette. The density to use is specified by the arg argument, zero gives single density while non-zero gives double density.

RXIOC_GETDENS
    Return the density of the diskette (zero or non-zero as above).

RXIOC_WDDMK
    On the next write, include a deleted data address mark in the header of the first sector.

RXIOC_RDDMK
    Return non-zero if the last sector read contained a deleted data address mark in its header, otherwise return 0.

FILES
/dev/rx?
/dev/rrx?[a-d]

DIAGNOSTICS

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.

rx%d: state %d (reset). The driver entered a bogus state. This should not happen.

ERRORS
The following errors may be returned by the driver:

[ENODEV]
    Drive not ready; usually because no disk is in the drive or the drive door is open.

[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.

[EIO]
    A physical error other than ``not ready'', probably bad media or unknown format.

[EBUSY]
    Drive has been opened for exclusive access.

[EBADF]
    No write access (on format), or wrong density; the latter can only happen if the disk is changed without closing the device (i.e., calling close(2)).

SEE ALSO
rxformat(8), newfs(8), tar(1), arff(8)

HISTORY
The rx driver appeared in 4.2BSD.

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.

If the drive subsystem is powered down when the machine is booted, the controller won't interrupt.