Selecting the Correct Statements About the LC-3 Trap Mechanism
What are the correct statements about the LC-3 Trap mechanism based on the provided information?
The LC-3 Trap Mechanism
Incorrect Statements
Now, let's explore the incorrect statements mentioned in the data:
1. There are 128 different possible TRAP addresses.
This statement is inaccurate. In reality, there are 256 possible TRAP addresses because the TRAP instruction is 8 bits long, allowing for 256 different values.
2. The LC-3 operating system places the TRAP routines below address ×3000.
This statement is incorrect. The TRAP routines are typically stored from address ×0100 to ×01FF, as stated in the data.
Conclusion
To summarize, the correct options regarding the LC-3 Trap mechanism are:
1. The return address is placed in R7 when the TRAP instruction executes.
2. The TRAP mechanism is used to provide system calls or service routines to programs.
3. The actual address of a trap routine is found by zero-extending bits 0 to 7 of the TRAP instruction and using this address to access the address of the trap routine.
4. The table of trap addresses is stored from address ×0100 to ×01FF.