ARM R4F, r1p3 manual System registers, VFPv3 architecture describes the following system registers

FPU Programmer’s Model

12.3System registers

The VFPv3 architecture describes the following system registers:

•Floating-Point System ID Register, FPSID on page 12-5

•Floating-Point Status and Control Register, FPSCR on page 12-6

•Floating-Point Exception Register, FPEXC on page 12-7

•Media and VFP Feature Registers, MVFR0 and MVFR1 on page 12-8.

Table 12-1shows the VFP system registers in the Cortex-R4F FPU.

Table 12-1 VFP system registers

Register	FMXR/FMRX <reg> field	Access type	Reset state
Floating-Point System ID Register, FPSID	b0000	Read-only	0x4102314xa
Floating-Point Status and Control Register, FPSCR	b0001	Read/write	0x00000000
Floating-Point Exception Register, FPEXC	b1000	Read/write	0x00000000
VFP Feature Register 0, MVFR0	b0111	Read-only	0x10110221
VFP Feature Register 1, MVFR1	b0110	Read-only	0x00000001

a. Bits [3:0] of the FPSID depend on the product revision. See the FPSID register description for more information.

Note

The FPSID, MVFR0, and MVFR1 Registers are read-only. Attempts to write these registers are ignored.

Table 12-2shows that some of the VFP system registers can only be accessed in Privileged modes.

Table 12-2 Accessing VFP system registers

	Privileged access		User access
Register	FPEXC EN=0	FPEXC EN=1	FPEXC EN=0	FPEXC EN=1
FPSID	Permitted	Permitted	Not permitted	Not permitted
FPSCR	Not permitted	Permitted	Not permitted	Permitted
MVFR0, MVFR1	Permitted	Permitted	Not permitted	Not permitted
FPEXC	Permitted	Permitted	Not permitted	Not permitted

Table 12-2shows that a Privileged mode is sometimes required to access a VFP system register. When a Privileged mode is required, an instruction that attempts to access a register in a nonprivileged mode takes the Undefined Instruction exception.

For a VFP system register to be accessible, it must follow the rules in Table 12-2and the VFP must also be accessible according to the Coprocessor Access Register. See c1, Coprocessor Access Register on page 4-44for more information.

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