* Question
What are the registers in the ARM state?
* Answer
In the ARM (Advanced RISC Machine) architecture, the registers are a crucial part of the processor’s state. ARM processors have a range of registers, divided into general-purpose registers, special-purpose registers, and status registers. Here is an overview of these registers in the ARM state:
General-Purpose Registers
– R0 to R12: These are general-purpose registers used for various operations, including arithmetic and data manipulation.
– R13 (SP): This is the stack pointer, used to point to the top of the stack.
– R14 (LR): This is the link register, used to store the return address when a function call is made.
– R15 (PC): This is the program counter, which holds the address of the next instruction to be executed.
Special-Purpose Registers
– CPSR (Current Program Status Register): This register holds the current state of the processor, including condition flags (N, Z, C, V), control bits, and processor mode bits.
– SPSR (Saved Program Status Register): This register is used to save the state of the CPSR when an exception occurs, allowing the processor to return to the previous state once the exception is handled.
Status Registers
– N (Negative): Indicates that the result of an operation was negative.
– Z (Zero): Indicates that the result of an operation was zero.
– C (Carry): Indicates that an operation resulted in a carry out or borrow.
– V (Overflow): Indicates that an arithmetic overflow has occurred.
Processor Modes
The ARM architecture supports several processor modes, each with its own set of banked registers. These modes include:
– User mode: The normal execution mode.
– FIQ (Fast Interrupt Request) mode: Used for high-priority interrupts.
– IRQ (Interrupt Request) mode: Used for standard interrupts.
– Supervisor mode: Used for operating system functions.
– Abort mode: Used to handle memory access violations.
– Undefined mode: Used to handle undefined instructions.
– System mode: Similar to user mode but with privileged access.
Each of these modes, except for the user and system modes, has its own set of banked registers for R13 and R14, which helps in handling context switches efficiently.
In summary, the ARM state consists of 16 general-purpose registers (R0 to R15), along with special-purpose registers like CPSR and SPSR, and condition flags within the CPSR that control the processor’s behavior. The ARM architecture’s design allows for efficient handling of various execution modes and interrupts.
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