Performance Measurement Support—Performance Counters

2.13 Performance Measurement Support—Performance Counters

The 21264/EV67 provides hardware support for two methods of obtaining program performance feedback information. The two methods do not require program modifica- tion. The first method offers similar capabilities to earlier microprocessor performance counters. The second method supports the new ProfileMe way of statistically sampling individual instructions during program execution to develop a model of program execu- tion. Both methods use the same hardware registers.

See Section 6.10 for information about counter control.

2.14 Floating-Point Control Register

The floating-point control register (FPCR) is shown in Figure 2–11.

Figure 2–11 Floating-Point Control Register

63 62 61 60 59 58 57 56 55 54 53 52 51 50 49 48 47

0

 

 

 

SUM

 

INED

 

UNFD

 

UNDZ

 

DYN

 

IOV

 

INE

 

UNF

 

OVF

 

DZE

 

INV

 

OVFD

 

DZED

 

INVD

 

DNZ

LK99-0050A

 

The floating-point control register fields are described in Table 2–14.

Table 2–14 Floating-Point Control Register Fields

Name

Extent

Type

Description

 

 

 

 

SUM

[63]

RW

Summary bit. Records bit-wise OR of FPCR exception bits.

INED

[62]

RW

Inexact Disable. If this bit is set and a floating-point instruction that enables

 

 

 

trapping on inexact results generates an inexact value, the result is placed in the

 

 

 

destination register and the trap is suppressed.

2–36Internal Architecture

Alpha 21264/EV67 Hardware Reference Manual

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Compaq EV67, 21264 specifications Performance Measurement Support-Performance Counters, Floating-Point Control Register