READ BUFFER | 6.Command Specification |
Table 6-73: READ BUFFER Header
Bit | 7 | 6 | 5 | 4 |
| 3 | 2 | 1 | 0 |
Byte |
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0 |
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| Reserved |
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1 | (MSB) |
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| Available Length |
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2 |
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3 |
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| (LSB) |
Available Length: This field specifies the total number of data bytes that are available in the target's data buffer. This number is not reduced to reflect the Allocation Length nor is it reduced to reflect the actual number of bytes written using the WRITE BUFFER command. Following the READ BUFFER header, the target will transfer data from its data buffer.
Data Mode (0010b) - in this mode, the
Buffer ID: The supported values are:
Table 6-74: Buffer ID values
Buffer ID | Description |
| Offset |
0 | Read Group Buffer | 0 | - 0x01000000 |
80 | Read Group Buffer | 0 | - 0x01000000 |
81 | Read Group Buffer | 0x01000000 - 0x02000000 | |
82 | Read Group Buffer | 0x02000000 - 0x03000000 | |
83 | Read Group Buffer | 0x03000000 - 0x03700000 | |
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If an unsupported Buffer ID code is requested, the drive returns a CHECK CONDITION status with an ILLEGAL REQUEST sense key set.
Descriptor Mode (0011b) - In this mode, a maximum of four bytes of READ BUFFER descriptor information is returned. The drive will return the descriptor information for the buffer specified by the BUFFER ID field (see the description of the buffer ID). If there is no buffer associated with the specified buffer ID, the drive will return all zeros in the READ BUFFER descriptor. The BUFFER OFFSET field is reserved in this mode. The allocation length will be set to four or greater. The drive will transfer the lesser of the allocation length or four bytes of READ BUFFER descriptor.
Table 6-75: READ BUFFER Descriptor
Bit | 7 | 6 | 5 | 4 |
| 3 | 2 | 1 | 0 |
Byte |
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0 |
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| Reserved |
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1 | (MSB) |
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| Buffer Capacity |
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2 |
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3 |
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Buffer Capacity: This field returns the size of the selected buffer in bytes.
Read Data from Echo Buffer (1011b) - Domain Validation is an important feature introduced in Ultra160 SCSI. It provides a mechanism for SCSI devices to perform at maximum possible operational data transfer speed. Domain validation performs a quick test to help ensure an initiator and target can actually transfer data at negotiated speeds. Using Echo Buffer option, the initiator can do a more extensive data transfer validation test. The initiator transmits the data using the WRITE BUFFER command with the echo buffer option and requests it back using the READ BUFFER command with echo buffer option.
Note: Refer to INCITS
SONY |
