Practice Questions for the multicycle implementation:

Andreas Moshovos

Spring 2007

Explain whether and how the datapath and the control need to change to support the following instructions:

1. Implement a load indirect (LDIND) instruction. Use opcode 0001 and fields R1 and R2 similar to the existing LOAD. LDIND R1 ((R2)) does the following:

R1 = MEM[MEM[R2]]

PC = PC + 1

2. Implement a “Jump and Link” (JAL) instruction. JAL takes a single argument which is a 4-bit signed immediate. Its format is similar to the branch instructions. JAL uses the 1110 opcode. It’s function is:

K1 = PC + 1

PC = PC + 1 + Sign-Extended(Imm4)

3. Implement a Jump Register instruction. It’s format uses bits 7 and 6 to specify a register, bits 5 and 4 are left unused and the lower four bits are 1100. JR R1 does PC = R1.