Question

1. In the MIPS architecture, where does the PC of a user program get saved when an interrupt occurs?

   		The Cause register
   		The $ra register
   		The EPC register
   		The $sp register

1 points   

QUESTION 4

1. Suppose we wish to call a function that accepts 2 input parameters (one 32 bit word each) and 1 return value (one 32 bit word). What is the minimum number of bytes that we should allocate on the stack to call this function. Assume all parameters and return values should go on the stack.

   		16 bytes
   		8 bytes
   		4 bytes
   		20 bytes
   		12 bytes

Answer 1

1.)

• When an interrupt occurs, all the contents of PC are moved to EPC register.
• After returning from the expception handler, the contents in EPC is moved back to PC
• Answer: The EPC register.

2.)

• It is given that every parameter and return value are to be stored in stack.
• The are two parameters of size 32 bits, each. So, in total they take up 64 bits.
• The return value is also of size 32 bits, so, in total 96 bits.
• 96 bits = 12 bytes.
• The return address of the function must be stored in stack too. It takes up 8 bytes of memory
• Total stack memory needed = 12+8 = 20 bytes
• Answer: 20 bytes