Fault Reset Flow

7.2 Fault Reset Flow

The fault reset sequence of operation is triggered by the assertion of the ClkFwdRst_H signal line. Figure 7–2shows the fault reset sequence of operation. The reset state machine is initially in RUN state. ClkFwdRst_H is asserted by the system, which causes the state machine to transition to the WAIT_FAULT_RESET state.

The 21264/EV68A internally resets a minimum amount of internal state. Note the effects of that reset on the IPRs in Table 7–5 .

Table 7–5 Effect on IPRs After Fault Reset

IPR

After Reset

 

 

PAL_BASE

Maintained (not reset)

I_CTL

Bit value = 3 (both Icaches are enabled)

PCTX[FPE]

Set

WRITE_MANY

Cleared (That is, the WRITE_MANY chain is initialized and the Bcache is turned off.)

EXC_ADDR

Set to an address that is close to the PC

 

 

The 21264/EV68A then waits for ClkFwdRst_H to deassert twice:

One deassert to transition directly to the WAIT_ClkFwdRst1 state without perform- ing any BiST

One deassert to initialize the clock forwarding interface

The 21264/EV68A then begins fetching code at PAL_BASE + 0x780.

Figure 7–2shows the fault reset sequence of operation. In Figure 7–2,note the follow- ing symbols for constraints and information:

Constraints:

A Min = 1 FrameClk_x cycle

Information:

aApproximately 264 GCLK cycles

bApproximately 525 GCLK cycles for external framing clock to be sampled and captured

c1 FrameClk_x cycle plus 2 GCLK cycles

eNext FrameClk_x rising edge

f3 FrameClk_x cycles

gApproximately 264 GCLK cycles to prevent first command from appearing too early

7–8

Initialization and Configuration

21264/EV68A Hardware Reference Manual

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Compaq EV68A specifications Fault Reset Flow, Effect on IPRs After Fault Reset