...
D0
D1
D2
D3
D14
D15
S0
S1
S2
S3
S4
S5
S6
S7
S28
S29
S30
S31
...
Functional Peripherals Description
89
SLAU356I – March 2015 – Revised June 2019
Copyright © 2015–2019, Texas Instruments Incorporated
Cortex-M4F Peripherals
Figure 2-2. FPU Register Bank
The mapping between the registers is as follows:
•
S<2n> maps to the least significant half of D<n>
•
S<2n+1> maps to the most significant half of D<n>
For example, you can access the least significant half of the value in D6 by accessing S12, and the most
significant half of the elements by accessing S13.
2.2.5.2
Modes of Operation
The control and status registers of FPU are listed in
.
The FPU provides three modes of operation to accommodate a variety of applications.
•
Full-Compliance mode: In Full-Compliance mode, the FPU processes all operations according to the
IEEE 754 standard in hardware.
•
Flush-to-Zero mode: Setting the FZ bit of the Floating-Point Status and Control Register (FPSCR)
enables Flush-to-Zero mode. In this mode, the FPU treats all subnormal input operands of arithmetic
CDP operations as zeros in the operation. Exceptions that result from a zero operand are signalled
appropriately. VABS, VNEG, and VMOV are not considered arithmetic CDP operations and are not
affected by Flush-to-Zero mode. A result that is tiny, as described in the IEEE 754 standard, where the
destination precision is smaller in magnitude than the minimum normal value before rounding, is
replaced with a zero. The IDC bit in FPSCR indicates when an input flush occurs. The UFC bit in
FPSCR indicates when a result flush occurs.
•
Default NaN mode: Setting the DN bit in the FPSCR register enables default NaN mode. In this mode,
the result of any arithmetic data processing operation that involves an input NaN, or that generates a
NaN result, returns the default NaN. Propagation of the fraction bits is maintained only by VABS,
VNEG, and VMOV operations. All other CDP operations ignore any information in the fraction bits of
an input NaN.
2.2.5.3
Compliance With the IEEE 754 Standard
When Default NaN (DN) and Flush-to-Zero (FZ) modes are disabled, FPv4 functionality is compliant with
the IEEE 754 standard in hardware. No support code is required to achieve this compliance.
2.2.5.4
Complete Implementation of the IEEE 754 Standard
The Cortex-M4F floating point instruction set does not support all operations defined in the IEEE
754-2008 standard. Unsupported operations include, but are not limited to the following:
•
Remainder
•
Round floating-point number to integer-valued floating-point number
•
Binary-to-decimal conversions