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21020285 D User’s Guide
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:
Description of
the Fields
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 read-in by the adapter for
execution. This value will be incremented by the adapter after it reads a new
Parameter Block; the value should never be changed from the Host side.
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.
Address
Offset
Byte memory Address
Offset + 0 Offset + 1 Offset + 2 Offset + 3
00H Parameter Block IN Index
04H Parameter Block OUT Index
08H Status Block IN Index
0CH Status Block OUT Index
10H Number of Parameter Blocks (n) (max = 2340)
14H Number of Status Blocks (y) (max = 4096)
18H Reserved
1CH Reserved
20H Parameter Block #1
3CH Parameter Block #2
. Parameter Blocks (up to #2340)
. Status Block #1
. Status Block #2
. Status Blocks (up to #4096)
Table 24: Command List Structure