The software interrupt instruction, SWI, of the ARM can be used by a program to call the operating system to request some service. The service being requested is specified in the low-order 8 bits of the instruction. Each of the services provided by the operating system is performed by a separate subroutine, and the starting addresses of these routines are stored in a table.

(a) Give one or more instructions that the operating system can use to copy the low- order 8 bits of the SWI instruction into a register.

(b) Give one or more instructions to call the appropriate service routine.