Intel i7-980X BX80613I7980X User Manual

54

Datasheet

These registers contain the initial read credits available for issuing memory reads. TAD 
read credit counters are loaded with the corresponding values at reset and anytime this 
register is written. BIOS must initialize this register with appropriate values depending 
on the level of Isoch support in the platform. It is invalid to write this register while TAD 
is active (has memory requests outstanding), as the write will break TAD's outstanding 
credit count values. 

Register programming rules:

• Total read credits (CRDT_RD + CRDT_RD_HIGH + CRDT_RD_CRIT) must not 

exceed 31.

• CRDT_RD_HIGH value must correspond to the number of high RTIDs reserved at 

the IOH.

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

the IOH.

• CRDT_RD_HIGH + CRDT_RD must be less than or equal to 13.
• 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 OR Sparing 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.

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.