CL-PS7500FE View Datasheet(PDF) - Cirrus Logic

Part Name

Description

Manufacturer

CL-PS7500FE

System-on-a Chip for Internet Appliance

Cirrus Logic 

CL-PS7500FE

System-on-a-Chip for Internet Appliance

Table 19-5. Flag Settings When the AC Bit in FPSR is Set

Flag

N

Z

C

V

Description

Less than

Equal

Greater than or equal or unordered

Unordered

NOTE: In this case, N and C are necessarily opposites.

19.4 FPA Instruction Set

The FPA and support software together implement the ARM floating point instruction set as defined in the

previous section. The FPA itself implements a subset of the instruction set as defined in Table 19-8.

The FPA does not however, execute arithmetic instructions in Section 19.2 if one or more of the operands

has one of the following exceptional values (also known as uncommon values):

q Infinity

q NaN

q Denormalized

q Illegal extended precision bit patterns

In this case the instruction is ‘bounced’ to the software support code for emulation.

19.4.1 Infinities and NaNs

Infinities and NaNs should occur very rarely in normal code. Although not common, there are a few ‘nor-

mal’ programs that frequently underflow and produce denormalized numbers. Handling of denormalized

operands in software can cause performance degradation. If necessary, this performance degradation

can be minimized by setting a bit in the Status register that disables support for denormalized numbers.

19.4.2 Exceptional Conditions

Certain other exceptional conditions that arise during an operation causes the FPA to transfer that oper-

ation to the support code. These conditions include all cases of the following IEEE exceptions:

q Invalid operation

q Division by zero

q Overflow

q Underflow

q Inexact

If the Inexact condition is detected, operation is only transferred to the support code if the Inexact trap

enable bit is set in the Floating Point Status register. Some other rare cases (such as, mantissa overflow

that occurs during the rounding stage of a Store Floating instruction) that do not in fact produce an IEEE

exception also traps to the support software.

180

FLOATING-POINT INSTRUCTION SET

ADVANCE DATA BOOK v2.0

June 1997

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