Intel Xeon L3406 CM80616005010AA User Manual

Datasheet, Volume 2

225

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 illegal 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 IIH.

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

the IIH.

• 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).

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

31:21

RO

0

20:16

RW

3

CRDT_RD_CRIT
Critical Read Credits.

15:13

RO

0

12:8

RW

1

CRDT_RD_HIGH
High Read Credits.

7:5

RO

0

4:0

RW

13

CRDT_RD
Normal Read Credits.