What are Program Status Registers in an ARM Processor?

What are Program Status Registers in ARM Processor?

Program Status Registers (PSRs) are special registers in an ARM processor that control system modes and interrupt handling. PSRs are used by the ARM processor to store information about the current state of the processor such as processor mode, interrupt enable/disable status, conditions codes, and other bits that affect processor operation.

Types of ARM Processor PSRs

There are two main types of PSRs – Application Program Status Registers (APSR) and System Program Status Registers (SPSR). Each type of PSR has different capabilities and functions. The APSR is used when the processor is running in user mode and provides information about the current state of the processor such as which interrupts are enabled, condition codes, and other bits that affect processor operation. The SPSR, on the other hand, is used when the processor is running in privileged or supervisor mode. It stores the state of all APSR registers when entering privileged or supervisor mode, and can be used to restore the state of the APSR when returning from privileged or supervisor mode.

ARM Processor Program Status Registers Usage

Program Status Registers are used to control ARM processor operation and control interrupts. PSRs are used to store the current state of the processor, and any changes to the PSRs will directly affect processor operation. In order to access the PSRs, privileged instructions must be used. Without these instructions, the processor cannot access the PSRs and any attempts to do so will result in a processor exception.

Conclusion

Program Status Registers are an integral part of the ARM processor architecture that allow for efficient control of the processor's operation and interrupt handling. The APSR and SPSR provide important information about the current state of the processor, and privileged instructions must be used to access the PSRs. Knowing the purpose and use of PSRs is essential for writing efficient ARM assembly code and debugging processor operations.