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