Specifications

ATAPI For Streaming Tape QIC-157 Rev B
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any, that may follow the last block descriptor. A block descriptor length of zero indicates that no block
descriptors are included in the mode parameter list. This condition shall not be considered an error.
Table 6-38 Mode Parameter Block Descriptor
Bit
Byte
7 6 5 4 3 2 1 0
0 Density Code
1 (MSB)
2 Number of Blocks
3 (LSB)
4 Reserved
5 (MSB)
6 Block Length
7 (LSB)
Block descriptors specify some of the medium characteristics. Support for block descriptors is
optional. Each block descriptor contains a density code field, a number of blocks field, and a block
length field. Block descriptor values are always current (i.e., saving is not supported).
The density code field is unique for each Device type. Refer to the mode parameters section of the
specific Device type for definition of this field.
Implementor's Note: Refer to Table 6-46 for a table of density codes for Streaming Tape Devices.
The number of blocks field specifies the number of logical blocks on the medium to which the density
code and block length fields apply. A value of zero indicates that all of the remaining logical blocks of
the Device shall have the medium characteristics specified.
Implementor's Note:
(1) There may be implicit association between parameters defined in the pages and block descriptors.
In this case, the Device may change parameters not explicitly sent with the MODE SELECT
command. A subsequent MODE SENSE command would reflect these changes.
(2) The number of remaining logical blocks may be unknown for some Device types.
The block length specifies the length in bytes of each logical block described by the block descriptor.
For QIC Streaming Tape Devices, two block sizes supported may be of either 512 or 1024 bytes per
block. Variable length blocks are not supported.
The mode page format is defined in Table 6-39.
Table 6-39 Mode Page Format
Bit
Byte
7 6 5 4 3 2 1 0
0 0 (PS) Reserved Page Code
1 Page Length (n - 1)
2 - n Mode Parameters
[Editor's Note: Due to hardware restrictions all mode parameters should be padded to a multiple of 4 bytes.]
Each mode page contains a page code, a page length, and a set of mode parameters. The page codes
are defined in Table 7-65 and in the mode parameter sub-sections of the specific Device type.