Intel Xeon E5502 80602E5502 User Manual

78

Intel® Xeon® Processor 5500 Series Datasheet, Volume 2

• CRDT_RD_HIGH + CRDT_RD must be less than or equal to 13 if High or Critical 

credits are nonzero.

• CRDT_RD_HIGH + CRDT_RD_CRIT must be less than or equal to 8.
• CRDT_RD_CRIT must be less than or equal to 6. Set CRDT_RD to (16 - 

CRDT_RD_CRIT - CRDT_RD_HIGH).

• If (Mirroring enabled) then Max for CRDT_RD is 14, otherwise it is 15. 
• If (Isoch not enabled) then CRDT_RD_HIGH and CRDT_RD_CRIT are set to 0.

Memory Controller Write Credit Thresholds. A Write threshold is defined as the number 
of credits reserved for this priority (or higher) request. It is required that High 
threshold be greater than or equal to Crit threshold, and that both be lower than the 
total Write Credit init value. BIOS must initialize this register with appropriate values 
depending on the level of Isoch support in the platform. The new values take effect 
immediately upon being written.

Register programming rules:

• CRIT threshold value must correspond to the number of critical RTIDs reserved at 

the IOH.

• HIGH threshold value must correspond to the sum of critical and high RTIDs 

reserved at the IOH (which must not exceed 30).

• Set MC_Channel_*_WAQ_PARAMS.ISOCENTRYTHRESHHOLD equal to (31-CRIT).

20:16

RW

3

CRDT_RD_CRIT. Critical Read Credits.

12:8

RW

1

CRDT_RD_HIGH. High Read Credits.

4:0

RW

13

CRDT_RD. Normal Read Credits.

12:8

RW

4

HIGH. High Credit Threshold. 

4:0

RW

3

CRIT. Critical Credit Threshold.