Bcache Port

When the Cbox CSR BC_BANK_ENABLE[0] is not set, the unused BcAdd_H[23:4] pins are tied to zero. For example, when configured as a 4MB cache, the 21264/EV67 never changes BcAdd_H[23:22] from logic zero, and when BC_BANK_ENABLE[0] is asserted, the 21264/EV67 drives the complement of the MSB index on the next higher BcAdd_H pin.

4.8.4.2 Bcache Control Pins

The Bcache control pins (BcLoad_L, BcDataWr_L, BcDataOE_L, BcTagWr_L, BcTagOE_L) are controlled using Cbox CSRs BC_BURST_MODE_ENABLE[0] and BC_PENTIUM_MODE[0].

Table 4–43shows the four combinations of Bcache control pin behavior obtained using the two CSRs.

Table 4–43 Programming the Bcache Control Pins

BC_PENTIUM_MODE

BC_BURST_MODE_ENABLE

RAM_TYPE

 

 

 

0

0

RAM_TYPE A

0

1

RAM_TYPE B

1

0

Unsupported

1

1

Unsupported

 

 

 

 

Table 4–44lists the combination of control pin assertion for

RAM_TYPE A.

 

Table 4–44 Control Pin Assertion for RAM_TYPE A

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

TYPE_A

NOP

RA0

RA1

RA2

RA3

NOP

NOP

WA0

WA1

WA2

WA3

NOP

 

 

 

 

 

 

 

 

 

 

 

 

 

BcLoad_L

H

H

H

H

H

H

H

H

H

H

H

H

BcDataOE_L

H

L

L

L

L

H

H

L

L

L

L

H

BcDataWr_L

H

H

H

H

H

H

H

L

L

L

L

H

BcTagOE_L

H

L

H

H

H

H

H

L

H

H

H

H

BcTagWr_L

H

H

H

H

H

H

H

L

H

H

H

H

 

 

 

 

 

 

 

 

 

 

 

 

 

Table 4–45lists the combination of control pin assertion for RAM_TYPE B.

Table 4–45 Control Pin Assertion for RAM_TYPE B

TYPE_B

NOP

RA0

RA1

RA2

RA3

NOP

NOP

WA0

WA1

WA2

WA3

NOP

BcLoad_L

H

L

H

H

H

H

H

L

H

H

H

H

BcDataOE_L

H

L

L

L

L

H

H

L

L

L

L

H

BcDataWr_L

L

H

H

H

H

L

L

L

L

L

L

L

BcTagOE_L

H

L

H

H

H

H

H

L

H

H

H

H

BcTagWr_L

H

H

H

H

H

H

H

L

H

H

H

H

 

 

 

 

 

 

 

 

 

 

 

 

 

4–52Cache and External Interfaces

Alpha 21264/EV67 Hardware Reference Manual

Page 140
Image 140
Compaq EV67, 21264 specifications 44lists the combination of control pin assertion for