System Port

Table 4–8 Program Values for Data-Sample/Drive CSRs (Continued)

CBOX CSR

Description

 

 

SYS_DDM_RD_RISE_EN[0]

Enables the sampling of incoming data on the rising edge of the incoming

 

forwarded clock. (Always asserted)

SYS_DDMF_ENABLE

Enables the falling edge of the system forwarded clock. (Always asserted)

SYS_DDMR_ENABLE

Enables the rising edge of the system forwarded clock. (Always asserted)

 

 

Table 4–9lists the program values for CSR SYS_FRAME_LD_VECTOR[4:0] that set the ratio between the forwarded clocks and the frame clock.

Table 4–9 Forwarded Clocks and Frame Clock Ratio

Clock Ratio

Transfer Mode

Value1

1:1

All

00

2:1

3.0X, 3.5X, 8.0X

1E

2:1

1.5X, 2.0X, 2.5X 4.0X, 5.0X, 6.0X 7.0X

1F

4:1

8X

15

4:1

1.5X, 4.0X, 5.0X, 6.0X, 7.0X

0B

4:1

3.0X, 3.5X

14

4:1

2.0X, 2.5X

0A

 

 

 

1These are hexadecimal values.

4.7.321264/EV68A-to-System Commands

This section describes the 21264/EV68A-to-system commands format and operation. The command, address, ID, and mask bits are transmitted in four consecutive cycles on SysAddOut_L[14:0]. The 21264/EV68A sends the command information in one of the two following modes as selected by the Cbox CSR bit.

Bank interleave on cache block boundary mode—SYSBUS_FORMAT[0] = 0

Page hit mode—SYSBUS_FORMAT[0] = 1

The physical address (PA) bits arrangements for the two modes is shown in Tables 4–10and 4–11.The purpose of the two modes is to give the system the PA bits that allow it to select the memory bank and drive the RAS address as soon as possible.

4.7.3.1 Bank Interleave on Cache Block Boundary Mode

Table 4–10shows the command format for the bank interleave on cache block bound- ary mode of operation (21264/EV68A-to-system).

Table 4–10 Bank Interleave on Cache Block Boundary Mode of Operation

 

 

SysAddOut_L[14:2]

SysAddOut_L[1]

SysAddOut_L[0]

 

 

 

 

 

 

Cycle 1

M1

Command[4:0]

PA[34:28]

PA[36]

PA[38]

 

 

 

 

 

 

21264/EV68A Hardware Reference Manual

Cache and External Interfaces 4–19

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Compaq specifications 3 21264/EV68A-to-System Commands, Forwarded Clocks and Frame Clock Ratio