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5–18 Internal Processor Registers
Alpha 21264/EV67 Hardware Reference Manual
Ibox IPRs
5.2.16 Ibox Status Register – I_STAT
The Ibox status register (I_STAT) is a read/write-1-to-clear register that contains Ibox
status information.
Usage of I_STAT in performance monitoring is described in Section 6.10.
Figure 5–23 shows the Ibox status register.
SBE[1:0] [9:8] RW,0 Stream Buffer Enable.
The value in this bit field specifies the number of Istream
buffer prefetches (besides the demand-fill) that are launched
after an Icache miss. If the value is zero, only demand
requests are launched.
SDE[1:0] [7:6] RW,0 PALshadow Register Enable.
Enables access to the PALshadow registers. If SDE[1] is set,
R4-R7 and R20-R23 are used as PALshadow registers.
SDE[0] does not affect 21264/EV67 operation.
SPE[2:0] [5:3] RW,0 Super Page Mode Enable.
Identical to the SPE bits in the Mbox M_CTL SPE[2:0]. See
Section 5.3.9.
IC_EN[1:0] [2:1] RW,3 Icache Set Enable.
At least one set must be enabled. The entire cache may be
enabled by setting both bits. Zero, one, or two Icache sets
can be enabled.
This bit does not clear the Icache, but only disables fills to
the affected set.
SPCE [0] RW,0 System Performance Counting Enable.
Enables performance counting for the entire system if indi-
vidual counters (PCTR0 or PCTR1) are enabled by setting
PCT0_EN or PCT1_EN, respectively.
Performance counting for individual processes can be
enabled by setting PCTX[PPCE]. See Section 5.2.21 for
more information.
See Section 6.10 for information about performance count-
ing.
Table 5–11 Ibox Control Register Fields Description (Continued)
Name Extent Type Description