How Trap Routine Addresses are Stored in LC-3 Instruction
How are trap routine addresses stored in the LC-3 instruction?
1. Why isn't the first instruction of the trap routine stored at the address specified in the TRAP instruction?
2. How can the semantics of the LC-3 TRAP instruction be modified to provide the starting address of the service routine?
Answer:
1. The starting address of the trap routine is stored at the address specified in the TRAP instruction so that the program can jump to the correct trap service routine based on the trap vector value.
2. Modifying the semantics of the LC-3 TRAP instruction can allow for the trap vector to provide the starting address of the service routine.
In LC-3 architecture, the starting address of the trap routine is stored at the address specified in the TRAP instruction instead of storing the first instruction directly at that address. This approach allows the program to efficiently jump to the correct trap service routine based on the value of the trap vector.
Modifying the semantics of the LC-3 TRAP instruction can provide a more flexible way to handle trap routines. By allowing the trap vector to specify the starting address of the service routine, multiple trap service routines can be implemented within the system.
The decision to store the starting address of the trap routine in the TRAP instruction address rather than the first instruction itself is crucial for enabling the system to support multiple trap service routines. It simplifies the process of identifying and executing the appropriate trap routine based on the specific trap vector value.
By modifying the semantics of the LC-3 TRAP instruction, developers can enhance the functionality of the instruction to cater to more diverse trap service routine requirements. This modification provides a more dynamic and scalable approach to handling traps in the LC-3 architecture.