Bcache Port

The Bcache supports the following multiples of the GCLK period: 1.5X (dual-data mode only), 2X, 2.5X, 3X, 3.5X, 4X, 5X, 6X, 7X, and 8X. However, the 21264/EV67 imposes a maximum Bcache clock period based on the SYSCLK ratio. Table 4–35lists the range of maximum Bcache clock periods. Section 4.7.8.2 describes fast mode.

Table 4–35 Range of Maximum Bcache Clock Ratios

 

Bcache Clock Ratio with Fast Mode

Bcache Clock Ratio with Fast Mode

SYSCLK Ratio

Enabled

Disabled

 

 

 

1.5X

4.0X

7.0X

2.0X

4.0X

7.0X

2.5X

5.0X

8.0X

3.0X

6.0X

8.0X

3.5X

7.0X

8.0X

4.0X

7.0X

8.0X

5.0X

8.0X

8.0X

6.0X

8.0X

8.0X

7.0X

8.0X

8.0X

8.0X

8.0X

8.0X

 

 

 

The 21264/EV67 provides a range of programmable Cbox CSRs to manipulate the Bcache port pins so that a variety of industry-standard SSRAMs can communicate effi- ciently with the 21264/EV67. The following SSRAMs can be used:.

Nonburst mode Reg/Reg late-write SSRAMs

Burst mode Reg/Reg late-write dual-data SSRAMs

4.8.1Bcache Port Pins

Table 3–1defines the 21264/EV67 signal types referred to in this section. Table 4–36lists the Bcache port pin groups along with their type, number, reference clock, and functional description.

Table 4–36 Bcache Port Pins

Pin Name

Type

Count

Reference Clock

Description

 

 

 

 

 

BcAdd_H[23:4]

O_PP

20

Int_Index_BcClk

Bcache index

BcCheck_H[15:0]

B_DA_PP

16

Int_Data_BcClk output

ECC check bits for BcData

 

 

 

BcDataInClk_H input

 

BcData_H[127:0]

B_DA_PP

128

Int_Data_BcClk output

Bcache data

 

 

 

BcDataInClk_H input

 

BcDataInClk_H[7:0]

I_DA

8

NA

Bcache data input clocks

BcDataOE_L

O_PP

1

Int_Index_BcClk

Bcache data output enable/chip

 

 

 

 

select

BcDataOutClk_H[3:0]

O_PP

8

NA

Bcache data clocks— high and low

BcDataOutClk_L[3:0]

 

 

 

version

Alpha 21264/EV67 Hardware Reference Manual

Cache and External Interfaces 4–43

Page 131
Image 131
Compaq 21264, EV67 specifications Bcache Port Pins, Range of Maximum Bcache Clock Ratios