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-rw-r--r--Documentation/ide/ide-tape.txt132
1 files changed, 65 insertions, 67 deletions
diff --git a/Documentation/ide/ide-tape.txt b/Documentation/ide/ide-tape.txt
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@@ -1,67 +1,65 @@
1/* 1IDE ATAPI streaming tape driver.
2 * IDE ATAPI streaming tape driver. 2
3 * 3This driver is a part of the Linux ide driver.
4 * This driver is a part of the Linux ide driver. 4
5 * 5The driver, in co-operation with ide.c, basically traverses the
6 * The driver, in co-operation with ide.c, basically traverses the 6request-list for the block device interface. The character device
7 * request-list for the block device interface. The character device 7interface, on the other hand, creates new requests, adds them
8 * interface, on the other hand, creates new requests, adds them 8to the request-list of the block device, and waits for their completion.
9 * to the request-list of the block device, and waits for their completion. 9
10 * 10The block device major and minor numbers are determined from the
11 * The block device major and minor numbers are determined from the 11tape's relative position in the ide interfaces, as explained in ide.c.
12 * tape's relative position in the ide interfaces, as explained in ide.c. 12
13 * 13The character device interface consists of the following devices:
14 * The character device interface consists of the following devices: 14
15 * 15ht0 major 37, minor 0 first IDE tape, rewind on close.
16 * ht0 major 37, minor 0 first IDE tape, rewind on close. 16ht1 major 37, minor 1 second IDE tape, rewind on close.
17 * ht1 major 37, minor 1 second IDE tape, rewind on close. 17...
18 * ... 18nht0 major 37, minor 128 first IDE tape, no rewind on close.
19 * nht0 major 37, minor 128 first IDE tape, no rewind on close. 19nht1 major 37, minor 129 second IDE tape, no rewind on close.
20 * nht1 major 37, minor 129 second IDE tape, no rewind on close. 20...
21 * ... 21
22 * 22The general magnetic tape commands compatible interface, as defined by
23 * The general magnetic tape commands compatible interface, as defined by 23include/linux/mtio.h, is accessible through the character device.
24 * include/linux/mtio.h, is accessible through the character device. 24
25 * 25General ide driver configuration options, such as the interrupt-unmask
26 * General ide driver configuration options, such as the interrupt-unmask 26flag, can be configured by issuing an ioctl to the block device interface,
27 * flag, can be configured by issuing an ioctl to the block device interface, 27as any other ide device.
28 * as any other ide device. 28
29 * 29Our own ide-tape ioctl's can be issued to either the block device or
30 * Our own ide-tape ioctl's can be issued to either the block device or 30the character device interface.
31 * the character device interface. 31
32 * 32Maximal throughput with minimal bus load will usually be achieved in the
33 * Maximal throughput with minimal bus load will usually be achieved in the 33following scenario:
34 * following scenario: 34
35 * 35 1. ide-tape is operating in the pipelined operation mode.
36 * 1. ide-tape is operating in the pipelined operation mode. 36 2. No buffering is performed by the user backup program.
37 * 2. No buffering is performed by the user backup program. 37
38 * 38Testing was done with a 2 GB CONNER CTMA 4000 IDE ATAPI Streaming Tape Drive.
39 * Testing was done with a 2 GB CONNER CTMA 4000 IDE ATAPI Streaming Tape Drive. 39
40 * 40Here are some words from the first releases of hd.c, which are quoted
41 * Here are some words from the first releases of hd.c, which are quoted 41in ide.c and apply here as well:
42 * in ide.c and apply here as well: 42
43 * 43| Special care is recommended. Have Fun!
44 * | Special care is recommended. Have Fun! 44
45 * 45Possible improvements:
46 * Possible improvements. 46
47 * 471. Support for the ATAPI overlap protocol.
48 * 1. Support for the ATAPI overlap protocol. 48
49 * 49In order to maximize bus throughput, we currently use the DSC
50 * In order to maximize bus throughput, we currently use the DSC 50overlap method which enables ide.c to service requests from the
51 * overlap method which enables ide.c to service requests from the 51other device while the tape is busy executing a command. The
52 * other device while the tape is busy executing a command. The 52DSC overlap method involves polling the tape's status register
53 * DSC overlap method involves polling the tape's status register 53for the DSC bit, and servicing the other device while the tape
54 * for the DSC bit, and servicing the other device while the tape 54isn't ready.
55 * isn't ready. 55
56 * 56In the current QIC development standard (December 1995),
57 * In the current QIC development standard (December 1995), 57it is recommended that new tape drives will *in addition*
58 * it is recommended that new tape drives will *in addition* 58implement the ATAPI overlap protocol, which is used for the
59 * implement the ATAPI overlap protocol, which is used for the 59same purpose - efficient use of the IDE bus, but is interrupt
60 * same purpose - efficient use of the IDE bus, but is interrupt 60driven and thus has much less CPU overhead.
61 * driven and thus has much less CPU overhead. 61
62 * 62ATAPI overlap is likely to be supported in most new ATAPI
63 * ATAPI overlap is likely to be supported in most new ATAPI 63devices, including new ATAPI cdroms, and thus provides us
64 * devices, including new ATAPI cdroms, and thus provides us 64a method by which we can achieve higher throughput when
65 * a method by which we can achieve higher throughput when 65sharing a (fast) ATA-2 disk with any (slow) new ATAPI device.
66 * sharing a (fast) ATA-2 disk with any (slow) new ATAPI device.
67 */