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Diffstat (limited to 'Documentation/ide')
-rw-r--r-- | Documentation/ide/ide-tape.txt | 132 |
1 files changed, 65 insertions, 67 deletions
diff --git a/Documentation/ide/ide-tape.txt b/Documentation/ide/ide-tape.txt index 51f596b282cd..3f348a0b21d8 100644 --- a/Documentation/ide/ide-tape.txt +++ b/Documentation/ide/ide-tape.txt | |||
@@ -1,67 +1,65 @@ | |||
1 | /* | 1 | IDE ATAPI streaming tape driver. |
2 | * IDE ATAPI streaming tape driver. | 2 | |
3 | * | 3 | This driver is a part of the Linux ide driver. |
4 | * This driver is a part of the Linux ide driver. | 4 | |
5 | * | 5 | The driver, in co-operation with ide.c, basically traverses the |
6 | * The driver, in co-operation with ide.c, basically traverses the | 6 | request-list for the block device interface. The character device |
7 | * request-list for the block device interface. The character device | 7 | interface, on the other hand, creates new requests, adds them |
8 | * interface, on the other hand, creates new requests, adds them | 8 | to 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 | * | 10 | The block device major and minor numbers are determined from the |
11 | * The block device major and minor numbers are determined from the | 11 | tape'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 | * | 13 | The character device interface consists of the following devices: |
14 | * The character device interface consists of the following devices: | 14 | |
15 | * | 15 | ht0 major 37, minor 0 first IDE tape, rewind on close. |
16 | * ht0 major 37, minor 0 first IDE tape, rewind on close. | 16 | ht1 major 37, minor 1 second IDE tape, rewind on close. |
17 | * ht1 major 37, minor 1 second IDE tape, rewind on close. | 17 | ... |
18 | * ... | 18 | nht0 major 37, minor 128 first IDE tape, no rewind on close. |
19 | * nht0 major 37, minor 128 first IDE tape, no rewind on close. | 19 | nht1 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 | * | 22 | The general magnetic tape commands compatible interface, as defined by |
23 | * The general magnetic tape commands compatible interface, as defined by | 23 | include/linux/mtio.h, is accessible through the character device. |
24 | * include/linux/mtio.h, is accessible through the character device. | 24 | |
25 | * | 25 | General ide driver configuration options, such as the interrupt-unmask |
26 | * General ide driver configuration options, such as the interrupt-unmask | 26 | flag, 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, | 27 | as any other ide device. |
28 | * as any other ide device. | 28 | |
29 | * | 29 | Our 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 | 30 | the character device interface. |
31 | * the character device interface. | 31 | |
32 | * | 32 | Maximal throughput with minimal bus load will usually be achieved in the |
33 | * Maximal throughput with minimal bus load will usually be achieved in the | 33 | following 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 | * | 38 | Testing 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 | * | 40 | Here 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 | 41 | in 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 | * | 45 | Possible improvements: |
46 | * Possible improvements. | 46 | |
47 | * | 47 | 1. Support for the ATAPI overlap protocol. |
48 | * 1. Support for the ATAPI overlap protocol. | 48 | |
49 | * | 49 | In order to maximize bus throughput, we currently use the DSC |
50 | * In order to maximize bus throughput, we currently use the DSC | 50 | overlap method which enables ide.c to service requests from the |
51 | * overlap method which enables ide.c to service requests from the | 51 | other device while the tape is busy executing a command. The |
52 | * other device while the tape is busy executing a command. The | 52 | DSC overlap method involves polling the tape's status register |
53 | * DSC overlap method involves polling the tape's status register | 53 | for the DSC bit, and servicing the other device while the tape |
54 | * for the DSC bit, and servicing the other device while the tape | 54 | isn't ready. |
55 | * isn't ready. | 55 | |
56 | * | 56 | In the current QIC development standard (December 1995), |
57 | * In the current QIC development standard (December 1995), | 57 | it is recommended that new tape drives will *in addition* |
58 | * it is recommended that new tape drives will *in addition* | 58 | implement the ATAPI overlap protocol, which is used for the |
59 | * implement the ATAPI overlap protocol, which is used for the | 59 | same purpose - efficient use of the IDE bus, but is interrupt |
60 | * same purpose - efficient use of the IDE bus, but is interrupt | 60 | driven and thus has much less CPU overhead. |
61 | * driven and thus has much less CPU overhead. | 61 | |
62 | * | 62 | ATAPI overlap is likely to be supported in most new ATAPI |
63 | * ATAPI overlap is likely to be supported in most new ATAPI | 63 | devices, including new ATAPI cdroms, and thus provides us |
64 | * devices, including new ATAPI cdroms, and thus provides us | 64 | a method by which we can achieve higher throughput when |
65 | * a method by which we can achieve higher throughput when | 65 | sharing 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 | */ | ||