Describe the integer register file in the ARM Cortex-M4 processor core: How many

Question

Describe the integer register file in the ARM Cortex-M4 processor core: How many registers are in the integer register file? How wide are they? Identify any special purpose registers and their functionality. The ARM v7-M architecture specifies an optional floating point coprocessor. Cortex-M4 processors with a floating point unit are identified with the M4F nomenclature. Describe the floating point unit: How many registers are in the floating point unit? How wide are they? How can the floating point unit be enabled?

Explanation / Answer

a register file is an array of processor registers. They are dependent on instruction set architecture.

The general purpose registers are 32 bit and are numbered from R0 to R12. There are stack pointers, link registers and program couners. Stack pointers are used in thread more. Its first bit ie, bit[1] is used for indication of which stack pointer is in use. On reset it loads msp from address 0x00000000 it is numbered R13

Link register is numbered as R14. It holds return value for exception, subroutines and function calls.

Program counter is for holding current program address, It is numbered as R15

ARM 7 is basically low cost processors optmized for low power consumer applications. They support Thumb 16 instructions set enabling 32 bit performance at 8/16 bits

There are 5 registers namely FPSID, FPSCR, MVFR0, MVFR1 and FPEXC. They are all 32 bit wide. to enable first define NSACR to use FPU in secure and/or non secure mode then you have to define CPACR and FPEXC. Then you need to set bits 10:11 of NSACR to have access to CP10 and CP11 which will enable secure and non secure mode for FPU.

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