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User’s Guide 21020285 D
Chapter 4 Command Operation
Using a Single Command Structure Page 4 - 11
Using a Single
Command
Structure
The Single Command structure is the fundamental means by which you can
issue a command to the RF3880 adapter board. To issue a command you must
perform each of these steps in the order described.
Set-up the
Structure in
memory
1. Clear 52 bytes of system memory at the location you wish to create the
Single Command structure.
2. Build a Parameter Block in bytes 0 through 28. Refer to Chapter 5 for
more information about Initiator Pass-through commands. Refer to
Chapter 7 if you wish to issue a Board-control command like Start
Command List.
3. Assign a value to the Interrupt field of the Single Command structure,
reflecting the interrupt the adapter should use and the ID by which it
will identify the interrupt being acknowledged by the Host. The
Reserved fields must be zero.
Prepare the
Hardware
Ports
4. If you are going to use this command to set bus width and byte/word
swapping, determine the appropriate value for the Control Field of the
Address Buffer Port.
5. Write the Control Field, Address Modifier and the two address words of
the Single Command structure to the Address Buffer Port on the
adapter.
6. Read the Status Port. Test the RDY bit (bit 1) to confirm that the board
is running. Next, verify that bit 0 (ENT) indicates the board is ready for
a Single Command. (On reset or power-up, this bit is set to zero.
Thereafter it toggles from its previous value to indicate readiness.)
Execute the
Command
7. Write a 0 value to the Channel Attention Port.
Determine
Command
Completion
8. When the command is complete, the adapter will write a Status Block in
bytes 36 through 52 of the Single Command structure and generate any
interrupt you requested. If you did not specify an interrupt level in the
structure, you must poll the CC bit of the Flags byte of the Status Block
to determine completion. Poll the ENT bit of the Status Port to
determine when you can issue another Single Command. Command
pre-fetch allows you to send another command to the adapter before the
previous is completed. Therefore, the CC and ENT bits are not
equivalent.