Compaq EV68A Programming the System Interface Clocks, Program Values for Data-Sample/Drive CSRs

Models: EV68A

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System Port

4.7.2 Programming the System Interface Clocks

The system forwarded clocks are free running and derived from the 21264/EV68A GCLK. The period of the system forwarded clocks is controlled by three Cbox CSRs, based on the bit-rate ratio (similar to the Bcache bit-rate ratio) except that all transfers are dual-data.

SYS_CLK_LD_VECTOR[15:0]

SYS_BPHASE_LD_VECTOR[3:0]

SYS_FDBK_EN[7:0]

Table 4–7lists the programming values used to program the system interface clocks.

Table 4–7 Programming Values for System Interface Clocks

System Transfer

SYS_CLK_LD_VECTOR1

SYS_BPHASE_LD_VECTOR1

SYS_FDBK_EN1

1.5X-DD

9249

5

02

2.0X-DD

3333

0

01

2.5X-DD

8C63

5

02

3.0X-DD

71C7

0

10

3.5X-DD

C387

A

04

4.0X-DD

0F0F

0

01

5.0X-DD

7C1F

0

40

6.0X-DD

F03F

0

10

7.0X-DD

C07F

0

04

8.0X-DD

00FF

0

01

 

 

 

 

1These are hexadecimal values.

In addition to programming of the clock CSRs, the data-sample/drive Cbox CSRs at the pads have to be set appropriately. Table 4–8shows the programmed values for these system CSRs. In Table 4–8,each system forwarded clock is the inversion of the low- assertion signal at the corresponding pin.

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

CBOX CSR

Description

 

 

SYS_DDM_FALL_EN[0]

Enables the update of 21264/EV68A system outputs based on the falling edge

 

of the system forwarded clock. (Always asserted)

SYS_DDM_RISE_EN[0]

Enables the update of 21264/EV68A system outputs based on the rising edge

 

of the system forwarded clock. (Always asserted)

SYS_DDM_RD_FALL_EN[0]

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

 

forwarded clock. (Always asserted)

4–18Cache and External Interfaces

21264/EV68A Hardware Reference Manual

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Compaq EV68A specifications Programming the System Interface Clocks, Programming Values for System Interface Clocks