PowerPC e500 Core Family Reference Manual, Rev. 1
10-4
Freescale Semiconductor
Auxiliary Processing Units (APUs)
10.4 Double-Precision Floating-Point APU (e500 v2 Only)
This section describes the double-precision floating-point APU. The vector and scalar
floating-point APUs are described in the EREF.
Except where otherwise noted, the double-precision floating-point APU adheres to the embedded
floating-point APUs programming model and notation conventions as described in the EREF.
10.4.1 Programming Model
Floating-point double-precision instructions operate on the entire 64 bits of the GPRs where a
floating-point data item consists of 64 bits. The double-precision floating-point APU uses the
thirty-two 64-bit GPRs, which is also used by the vector single-precision floating-point APU and
the signal-processing engine (SPE) APU.
There are no record forms of embedded floating-point instructions. Floating-point compare
instructions treat NaNs, Infinity and Denorm as normalized numbers for the comparison
calculation when default results are provided.
•
SPE floating-point status and control register (SPEFSCR)—Double-precision
floating-point operations use the SPEFSCR as it is described in the EREF.
Double-precision floating-point instructions affect only the low element floating-point
status flags and leave the high element floating-point status flags undefined.
•
Embedded floating-point exception bit in ESR. The double-precision floating-point APU is
affected by the embedded floating-point exception bit, ESR[SPE], as it is described in the
EREF. This bit is set whenever the processor takes an interrupt related to the execution of
the embedded floating-point instructions.
The double-precision floating-point APU can generate the following embedded floating-point
APU interrupts as described in the EREF:
•
SPE/embedded floating-point unavailable interrupt—IVOR32 (SPR 528)
•
Embedded floating-point data interrupt—IVOR33 (SPR 529)
•
Embedded floating-point round interrupt—IVOR34 (SPR 530)
10.4.2 Double-Precision Floating-Point APU Operations
This section describes operational modes and formats. Note that IEEE 754–compliance and sticky
bit handling for exception conditions is as described in the EREF.
10.4.2.1 Operational Modes
Double-precision floating-point operations are governed by the setting of the mode bit in SPESCR.
The mode bit defines how floating-point results are computed and how floating-point exceptions
Summary of Contents for PowerPC e500 Core
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