2 * IDE ATAPI streaming tape driver.
4 * This driver is a part of the Linux ide driver.
6 * The driver, in co-operation with ide.c, basically traverses the
7 * request-list for the block device interface. The character device
8 * interface, on the other hand, creates new requests, adds them
9 * to the request-list of the block device, and waits for their completion.
11 * The block device major and minor numbers are determined from the
12 * tape's relative position in the ide interfaces, as explained in ide.c.
14 * The character device interface consists of the following devices:
16 * ht0 major 37, minor 0 first IDE tape, rewind on close.
17 * ht1 major 37, minor 1 second IDE tape, rewind on close.
19 * nht0 major 37, minor 128 first IDE tape, no rewind on close.
20 * nht1 major 37, minor 129 second IDE tape, no rewind on close.
23 * The general magnetic tape commands compatible interface, as defined by
24 * include/linux/mtio.h, is accessible through the character device.
26 * General ide driver configuration options, such as the interrupt-unmask
27 * flag, can be configured by issuing an ioctl to the block device interface,
28 * as any other ide device.
30 * Our own ide-tape ioctl's can be issued to either the block device or
31 * the character device interface.
33 * Maximal throughput with minimal bus load will usually be achieved in the
36 * 1. ide-tape is operating in the pipelined operation mode.
37 * 2. No buffering is performed by the user backup program.
39 * Testing was done with a 2 GB CONNER CTMA 4000 IDE ATAPI Streaming Tape Drive.
41 * Here are some words from the first releases of hd.c, which are quoted
42 * in ide.c and apply here as well:
44 * | Special care is recommended. Have Fun!
46 * Possible improvements.
48 * 1. Support for the ATAPI overlap protocol.
50 * In order to maximize bus throughput, we currently use the DSC
51 * overlap method which enables ide.c to service requests from the
52 * other device while the tape is busy executing a command. The
53 * DSC overlap method involves polling the tape's status register
54 * for the DSC bit, and servicing the other device while the tape
57 * In the current QIC development standard (December 1995),
58 * it is recommended that new tape drives will *in addition*
59 * implement the ATAPI overlap protocol, which is used for the
60 * same purpose - efficient use of the IDE bus, but is interrupt
61 * driven and thus has much less CPU overhead.
63 * ATAPI overlap is likely to be supported in most new ATAPI
64 * devices, including new ATAPI cdroms, and thus provides us
65 * a method by which we can achieve higher throughput when
66 * sharing a (fast) ATA-2 disk with any (slow) new ATAPI device.