Chapter 3 - MACSI Host Interface

Command Options

Table 3-30. Command Options

Command Options

Offst

15

14

13

12

11

10

9

8

7

6

5

4

3

2

1

0

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

0x01

 

 

 

 

 

 

RSV

 

DMC

 

Port

 

IG

RSV

RSV

IE

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Interrupt enable (IE)

As defined in Common IOPB Structures.

In-line gather (IG)

Setting this bit allows the host to define the frame location in system memory as a set of address/count pairs. These gather elements are specified directly in the remainder of the IOPB, and do not require a separate DMA of a gather-list.

Port selector

This field specifies the port to which the frame will be transmitted. Valid ports range from 0 to 3.

Disable multiple completion (DMC)

Setting this bit prevents the frame from being returned using the multiple completion mechanism.

Reserved bit (RSV)

Any bit marked Reserved must be set to zero. Failure to do so will cause an error to be returned to the host.

Transmit -- In-Line Gathers

By setting the IG bit in the Command Options field, the driver may define the data space for the frame to be transmitted as a set of address/count pairs, or a gather list. By incorporating this directly in the Transmit IOPB, the controller saves a separate DMA transfer of the gather list before beginning the DMA of the frame itself.

The gather list begins with the element immediately after the DMA Transfer Control Word (which controls the transfer of each of the elements), and can continue for up to 8 elements. Note that if more than 2 elements are included, that the resulting size of the IOPB exceeds normal, and the IOPB length field in the CQE must be set in order for the controller to correctly process the command. This also means that fewer Command Queue Entries can be located in short I/O if onboard IOPBs are employed.

Also note that the fields have been set up for long-word alignment to the structure elements, at the expense of supporting fewer onboard CQE/IOPB’s. This is to accommodate RISC-based systems which make non-longword aligned accesses difficult and expensive.

88