Chapter 4 Command Operation
Page 4 - 18 |
| Command List Structure |
Command List Structure
The previous pages have discussed the use of a Single Command Structure to issue a command to the RF3880 adapter. This section deals with the other method of operation: the Command List Structure. With this structure you are able to queue commands for execution; use of the Command List Structure enhances performance by decreasing command overhead and allowing both system and adapter to perform command I/O at the same time.
Format of
Command List
Structure
The address of the Command List Structure should be on a double word boundary. The Command List Structure is illustrated for you below:
Address |
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| Byte memory Address |
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Offset | Offset + 0 |
| Offset + 1 |
| Offset + 2 |
| Offset + 3 |
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00H |
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| Parameter Block IN Index |
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04H |
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| Parameter Block OUT Index |
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08H |
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| Status Block IN Index |
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0CH |
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| Status Block OUT Index |
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10H |
| Number of Parameter Blocks (n) (max = 2340) |
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14H |
| Number of Status Blocks (y) (max = 4096) |
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18H |
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| Reserved |
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1CH |
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| Reserved |
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20H |
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| Parameter Block #1 |
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3CH |
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| Parameter Block #2 |
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. |
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| Parameter Blocks (up to #2340) |
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. |
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| Status Block #1 |
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. |
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| Status Block #2 |
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. |
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| Status Blocks (up to #4096) |
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Description of the Fields
Table 24: Command List Structure
The following section describes the information you will need to properly complete a Command List Structure.
Parameter Block IN Index
This field contains an index into the Parameter Block array. It points to the next open block. When you add a Parameter Block to the Command List Structure, you must increment this number. This value is never changed from the adapter side of operations.
Parameter Block OUT Index
This field also contains an index into the Parameter Block array, but it points to the next Parameter Block in the structure to be
Status Block IN Index
The Status Block IN field is incremented each time a Status Block is placed into the Status Block array by the adapter. This value should never be changed from the Host side.
21020285 D | User’s Guide |
