DP83266 datasheet(122/152 Pages) NSC

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70 Control Information (Continued)

REQ Descriptor (REQ)

Request Descriptors (REQs) contain the part byte address and size of one or more Output Data Unit Descriptors They also

contain parameters and commands to the MACSI device associated with Request operations

Multiple REQ Descriptors (parts) may be grouped as one Request Descriptor object by the host software with the REQFirst

defining the parameters for the entire Request object Also multiple Output Data Unit Descriptors may be grouped contiguously

to be described by a single REQ Descriptor

Each REQ part is fetched by the MACSI device from the Request Channel’s REQ Descriptor Queue using the REQ Queue

Pointer Register Each Request Channel processes one Request Object (REQOnly or REQFirst to REQLast set) per service

opportunity

The MACSI device checks for the following inconsistencies when the REQ is loaded from memory

1 REQFirst with invalid Confirmation Class (as shown in the

Figure 7-7 )

2 REQFirst with Request Class e 0

3 REQFirst when the previous REQ was not a REQLast or REQOnly

4 REQ which is not a REQFirst or REQOnly when the previous REQ was a REQLast or a REQOnly

When an inconsistency is detected the MACSI device aborts the Request and reports the exception in the Request Status field

of the CNF Descriptor

The encodings of the RQCLS and CNFCLS bits are described in more detail in

Figure 7-6 and Figure 7-7 respectively

RES

UID

SIZE

CNFCLS

RQCLS

Word 0

F-L

RES

LOC

Word 1

Bit

Symbol

Description

Word 0

D7–D0

Frame Control

This specifies the Frame control field to be used unless FC transparency is enabled

This field is decoded to determine whether to assert RQCLM or RQBCN This decoding is always

active ie regardless of frame control transparency This field is also used for comparing received

frames when confirming (without FC transparency)

D8 – D11

RQCLS

RequestRelease Class

This field encodes the Request Class for the entire Request object and is

thus only sampled on a REQFirst or REQOnly The field is asserted on the RQRCLS signals to the

Ring Engine when requesting a token If the Request Class is incompatible with the current ring state

the MACSI device sets the RCHN’s USR bit in the Request Attention Register The encoding of this

field is shown in

Figure 7-6

D15 – D12

CNFCLS

Confirmation Class

This field encodes the Confirmation Class for the entire Request object and is

only sampled on a REQFirst or REQOnly The encoding of this field is shown in

Figure 7-7

D12

End

Enables confirmation on completion of request

CNFs on completion disabled

CNFs on completion enabled

D13

Intermediate

Enables Intermediate (at the end of each Service Opportunity) Confirmation

Intermediate CNFs disabled

Intermediate CNFs enabled

D14

FullTransmitter

Selects between Transmitter and Full Confirmation

Transmitter confirm

Full confirm

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