Compaq EV68A specifications Bcache Port

Models: EV68A

1 356
Download 356 pages 47.63 Kb
Page 130
Image 130

Bcache Port

4.7.10.2 System Probes and SysDc Commands

Ordering of cache transactions at the system serialization point must be reflected in the 21264/EV68A cache system. Table 4–34shows the rules that a system must follow to control the order of cache status update within the 21264/EV68A cache structures (including the VAF) at the 21264/EV68A pins.

Table 4–34 Rules for System Control of Cache Status Update Order

First

Second

Rule

 

 

 

Probe

Probe

To control the sequence of cache status updates between probes, systems

 

 

can present the probes in order to the 21264/EV68A, and the 21264/

 

 

EV68A will update the appropriate cache state (including the VAF) in

 

 

order.

Probe

SysDc MAF

To ensure that a probe updates the internal cache status before a SysDc

 

 

MAF transaction (including fills and ChangeToDirtySuccess commands),

 

 

systems must wait for the probe response before presenting the SysDc

 

 

MAF command to the 21264/EV68A. To ensure that a probe updates a

 

 

VAF entry before a SysDc VAF (release buffer), systems must wait for the

 

 

probe response.

Probe

SysDc VAF

Same as Probe/SysDc MAF, above.

SysDc MAF

Probe

To ensure that a SysDc MAF command updates the 21264/EV68A cache

 

 

system before a probe to the same address, systems must deliver the D1

 

 

(the second QW of data delivered to the 21264/EV68A) before or in the

 

 

same cycle as the A3 of the probe (the last cycle of the 4-cycle probe com-

 

 

mand). This rule also applies to ChangeToDirtySuccess commands that

 

 

have a virtual D0 and D1 transaction.

SysDc MAF

SysDc MAF

SysDc MAF transactions can be ordered into the 21264/EV68A by order-

 

 

ing them appropriately at the 21264/EV68A interface.

SysDc MAF

SysDc VAF

SysDc MAF transactions and SysDc VAF transactions cannot interact

 

 

within the 21264/EV68A because the 21264/EV68A does not generate

 

 

MAF transactions to the same address as existing VAF transactions.

SysDc VAF

Probe

To ensure that a SysDc VAF invalidates a VAF entry before a probe to the

 

 

same address, the SysDc VAF command must precede the first cycle of the

 

 

4-cycle probe command.

SysDc VAF

SysDc MAF

SysDc MAF transactions and SysDc VAF transactions cannot interact

 

 

within the 21264/EV68A because the 21264/EV68A does not generate

 

 

MAF transactions to the same address as existing VAF transactions.

SysDc VAF

SysDc VAF

SysDc VAF transactions can be ordered into the 21264/EV68A by order-

 

 

ing them appropriately at the 21264/EV68A interface.

 

 

 

4.8 Bcache Port

The 21264/EV68A supports a second-level cache (Bcache) with 64-byte blocks. The Bcache size can be 1MB, 2MB, 4MB, 8MB, or 16MB. The Bcache port has a 144-bit data bus that is used for data transfers between the 21264/EV68A and the Bcache. All Bcache control and address signal lines are clocked synchronously on Bcache clock cycle boundaries.

4–42Cache and External Interfaces

21264/EV68A Hardware Reference Manual

Page 130
Image 130
Compaq EV68A specifications Bcache Port