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21020285 D User’s Guide
Chapter 4 Command Operation
Page 4 - 20 Creating the Command List Structure
Creating the
Command List
Structure
To create a Command List Structure you should perform the following steps
in the order indicated:
1. Select and clear a portion of memory that will contain the Command
List. The Command List should start on a double word boundary.
Enough space should be allocated to accommodate the Index
information plus the Parameter and Status Blocks. Use the following
information to determine the amount of space to allocate. (The value n
is the number of Parameter Blocks and the value y is the number of
Status Blocks to be held in each respective array.):
Index information = 32 bytes
Parameter Block array = n x 28 bytes
Status Block array = y x 16 bytes
Zero the indexes and set-up the Number of Parameter Blocks and Number of
Status Block fields.
2. Issue a Start Command List command to the adapter within a Single
Command Structure. An example of how to do this can be found on
page 4 - 12.
3. Create Parameter Blocks in the reserved space, update the Parameter
Block IN index. Write a 1 to the Channel Attention Port to begin
execution.
4. Retrieve Status Blocks from the Status Block reserved area. Update the
Status Block OUT index.