2008-04-27 21:38:28 +08:00
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IDE ATAPI streaming tape driver.
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This driver is a part of the Linux ide driver.
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The driver, in co-operation with ide.c, basically traverses the
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request-list for the block device interface. The character device
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interface, on the other hand, creates new requests, adds them
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to the request-list of the block device, and waits for their completion.
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The block device major and minor numbers are determined from the
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tape's relative position in the ide interfaces, as explained in ide.c.
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The character device interface consists of the following devices:
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ht0 major 37, minor 0 first IDE tape, rewind on close.
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ht1 major 37, minor 1 second IDE tape, rewind on close.
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...
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nht0 major 37, minor 128 first IDE tape, no rewind on close.
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nht1 major 37, minor 129 second IDE tape, no rewind on close.
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...
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The general magnetic tape commands compatible interface, as defined by
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include/linux/mtio.h, is accessible through the character device.
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General ide driver configuration options, such as the interrupt-unmask
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flag, can be configured by issuing an ioctl to the block device interface,
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as any other ide device.
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Our own ide-tape ioctl's can be issued to either the block device or
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the character device interface.
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Maximal throughput with minimal bus load will usually be achieved in the
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following scenario:
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1. ide-tape is operating in the pipelined operation mode.
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2. No buffering is performed by the user backup program.
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Testing was done with a 2 GB CONNER CTMA 4000 IDE ATAPI Streaming Tape Drive.
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Here are some words from the first releases of hd.c, which are quoted
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in ide.c and apply here as well:
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| Special care is recommended. Have Fun!
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Possible improvements:
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1. Support for the ATAPI overlap protocol.
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In order to maximize bus throughput, we currently use the DSC
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overlap method which enables ide.c to service requests from the
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other device while the tape is busy executing a command. The
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DSC overlap method involves polling the tape's status register
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for the DSC bit, and servicing the other device while the tape
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isn't ready.
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In the current QIC development standard (December 1995),
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it is recommended that new tape drives will *in addition*
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implement the ATAPI overlap protocol, which is used for the
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same purpose - efficient use of the IDE bus, but is interrupt
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driven and thus has much less CPU overhead.
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ATAPI overlap is likely to be supported in most new ATAPI
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devices, including new ATAPI cdroms, and thus provides us
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a method by which we can achieve higher throughput when
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sharing a (fast) ATA-2 disk with any (slow) new ATAPI device.
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