Software Interrupt Instruction in ARM Processor

Software Interrupt Instruction in ARM Processor

The ARM processor is a popular choice for embedded systems and its powerful instruction set is a major part of its success. One unique instruction found in the ARM processor is the software interrupt instruction, also known as the SWI instruction. This instruction can be used to initiate a call to a subroutine located in an external memory such as ROM, RAM, or even external peripherals.

The SWI instruction is a 32-bit instruction that contains 8-bits of data, called a function code. This function code is used to identify the type of service requested by the processor. It is possible to have up to 256 different functions for a single SWI instruction, which makes it very useful for a variety of applications.

The SWI instruction operates on the principle of "told what to do, not how to do it." This means that the processor does not need to know the specifics of how the service should operate. Instead, it simply transfers control to an external routine that can provide the appropriate functionality.

When using the SWI instruction, the processor first loads the SWI's function code into a register. The processor then jumps to a fixed address, which is at the start of the external routine that is supposed to service the request described in the function code. This routine is responsible for interpreting the function code and making sure the proper operations are performed.

The SWI instruction is a very powerful feature of the ARM processor, and is especially useful for calling services from external sources. By using this instruction, the processor can easily take advantage of a wide range of services and make sure that they are performed in a timely and reliable manner.