Compaq 21264 - Manual (Page 159)

Alpha 21264/EV67 Hardware Reference Manual Internal Processor Registers 5–17
Ibox IPRs
MCHK_EN [21] RW,0 Machine check enable — set to enable machine checks.
ST_WAIT_64K [20] RW,0 The stWait table is used to reduce load/store order traps.
When set, the stWait table is cleared after 64K cycles. When
clear, the stWait table is cleared after 16K cycles. See Sec-
tion 2.11.
PCT1_EN [19] RW,0 Enable performance counter #1. If this bit is one, the perfor-
mance counter will count if either the system (SPCE) or pro-
cess (PPCE) performance counter enable is asserted.
PCT0_EN [18] RW,0 Enable performance counter #0. If this bit is one, the perfor-
mance counter will count if EITHER the system (SPCE) or
process (PPCE) performance counter enable is set.
SINGLE_ISSUE_H [17] RW,0 When set, this bit forces instructions to issue only from the
bottom-most entries of the IQ and FQ.
VA_FORM_32 [16] RW,0 This bit controls address formatting on a read of the
IVA_FORM register.
VA_48 [15] RW,0 This bit controls the format applied to effective virtual
addresses by the IVA_FORM register and the Ibox virtual
address sign extension checkers. When VA_48 is clear, 43-
bit virtual address format is used, and when VA_48 is set,
48-bit virtual address format is used. The effect of this bit on
the IVA_FORM register is identical to the effect of
VA_CTL[VA_48] on the VA_FORM register. See Section
5.1.5.
When VA_48 is set, the sign extension checkers generate an
ACV if va[63:0]
≠
SEXT(va[47:0]). When VA_48 is clear,
the sign extension checkers generate an ACV if va[63:0]
≠
SEXT(va[42:0]).
This bit also affects DTB_DOUBLE traps. If set, the DTB
double miss traps vector to the DTB_DOUBLE_4 entry
point.
DTB_DOUBLE PALcode flow selection is not affected by
VA_CTL[VA_48].
SL_RCV [14] RO See Section 11.2.
SL_XMIT [13] WO When set, drives a value on SromClk_H. See Section 11.2.
HWE [12] RW,0 If set, allow PALRES intructions to be executed in kernel
mode. Note that modification of the ITB while in kernel
mode/native mode may cause UNPREDICTABLE behavior.
BP_MODE[1:0] [11:10] RW,0 Branch Prediction Mode Selection.
BP_MODE[1], if set, forces all branches to be predicted to
fall through. If clear, the dynamic branch predictor is chosen.
BP_MODE[0]. If set, the dynamic branch predictor chooses
local history prediction. If clear, the dynamic branch predic-
tor chooses local or global prediction based on the state of
the chooser.
Table 5–11 Ibox Control Register Fields Description (Continued)
Name Extent Type Description