ARM Cortex R4F - Manual (Page 345)

FPU Programmer’s Model
ARM DDI 0363E Copyright © 2009 ARM Limited. All rights reserved. 12-4
ID013010 Non-Confidential, Unrestricted Access
12.3 System 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 12-1 shows the VFP system registers in the Cortex-R4F FPU.
Note
The FPSID, MVFR0, and MVFR1 Registers are read-only. Attempts to write these registers are
ignored.
Table 12-2 shows that some of the VFP system registers can only be accessed in Privileged
modes.
Table 12-2 shows 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 12-2 and the VFP
must also be accessible according to the Coprocessor Access Register. See c1, Coprocessor
Access Register on page 4-44 for more information.
Table 12-1 VFP system registers
Register FMXR/FMRX <reg> field Access type Reset state
Floating-Point System ID Register, FPSID b0000 Read-only
0x4102314x a
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.
Table 12-2 Accessing VFP system registers
Register
Privileged access User access
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