User`s manual

Scatter/Gather List

SBCSCSI/D1 B-17

Scatter/Gather List

The scatter/gather list is initialized by the user and allocated to the Firmware

with the command structure. The Firmware may modify the scatter/gather

list in the case of a disconnect. Below is an example of a scatter/gather list with

two entries. For this example list, the user would place 0x00004000 in the

Scatter/Gather List Pointer (Data Pointer) field of the command structure and

set the S/G bit in the command control field. A scatter/gather list must be

aligned on a four-byte boundary (longword boundary for the CISC

MVME167; word boundary for the RISC MVME187).

Byte Count

Byte count is the number of bytes to transfer for this entry of the scatter/gather

list. The value in this field must not exceed 0xFFFFFF (16,777,215).

Buffer Pointer

This is a pointer to the area where the data is to be transferred.

Logical End

The last entry in a scatter/gather list is the logical end of list. This entry must

be all zeroes.

Table B-3. Example Scatter/Gather List

Address Parameter

0x4000 24 bit Byte Count

0x4004 Buffer Pointer

0x4008 24 bit Byte Count

0x400C Buffer Pointer

0x4010 Logical End (32 bit value = 0)

0x4014 don't care