RISCV mepc mecause and mtval

mtval (Machine Trap Value):
- The mtval register is a machine-level register used to store the value associated with an exception or trap.
- When an exception or trap occurs, the value causing the exception, such as the faulting address or data, is stored in the mtval register.
- The content and interpretation of the mtval register depend on the specific exception or trap that occurred.
- Software handlers can examine the value stored in mtval to gain insights into the cause or nature of the exception and take appropriate actions based on that information.
mepc (Machine Exception Program Counter):
- The mepc register is a machine-level register that holds the program counter value at the time an exception or trap occurs.
- When an exception or trap interrupts the normal program execution, the address of the instruction that was being executed is stored in the mepc register.
- The mepc register is used during the exception handling process to determine the correct point to resume program execution once the exception is handled.
- Software handlers can read the value from mepc to identify the exact location in the program where the exception occurred and take appropriate actions accordingly.
mecause (Machine Exception Cause):
- The mecause register is a machine-level register that indicates the cause of an exception or trap.
- It stores a code or identifier that represents the specific exception or trap that occurred.
- The mecause register is essential for exception handlers to determine the type of exception or trap and handle it accordingly.
- Software handlers can read the value from mecause to identify the specific exception that occurred, such as an illegal instruction, a page fault, or an external interrupt.