Assignment Project: Multi‐Cycle Datapath Adding instructions
Students will work in groups of no less than 2 and no more than 3. All groups will present their work to the class in the last week (i.e. between 14/5/2023
to 18/5/2023) with no exceptions, and submit their report to me on course Moodle for grading.
1. Datapath Modification
Modify the datapath and control signals to perform the new instructions in the corresponding datapath. Use the minimal amount of additional hardware and
clock cycles/control states.
Remember:
When adding new instructions, don't break the operation of the standard ones.
Avoid adding ALUs, adders, Reg Files, or memories to the datapath
You can add MUXes, logic gates, etc. but try to do minimally. (these cost in terms of area, cycle time, etc)
You can add or remove step(s) to the datapath execution if it’s necessary, but try to do minimally
The new Instruction to be added to the standard multicycle datapath
1. Load Word Register (uses R instruction format)
lwr Rt, Rd (Rs) #Reg[Rt] = Mem[Reg[Rd]+Reg[Rs]]
2. Add 3 operands (new instruction format: opcode(6), rs(5), rt(5), rd(5), rx(5), (6 bits not used))
add3 Rd, Rs, Rt, Rx #Reg[Rd] = Reg[Rs] + Reg[Rt] + Reg[Rx]
3. Add to Memory (new instruction format: opcode(6), rs(5), rt(5), rd(5), offset(11))
addm Rd, Rt, Offset(Rs) #Reg[Rd] = Reg[Rt] + Mem[sign extended offset + Reg[Rs]]
4. Branch on less than or Equal (uses I instruction format)
blez Rs, label # if Reg[Rs] < 0, PC = PC+4 + (sign‐extended offset << 2)
5. Branch Equal to Memory (new instruction format: opcode(6), rs(5), rt(5), rd(5), offset(11))
beqm Rd, Rt, Offset(Rs) # if Reg[Rt] = Mem[Offset+Reg[Rs]], PC = PC + 4 + Reg[Rd]
6. Branch Equal to 0 to Immediate (uses R instruction format)
beqzi (Rs), Label #if Mem[Reg[Rs]] = 0, then PC = PC + (sign‐extended offset) (NOTE: This is not PC+4, and not shifted by 2)
7. Store Word and Increment
swinc Rt, offset(Rs) #Mem[Reg[Rs] + sign extended offset]= Reg[Rt], Reg[Rs] = Reg[Rs] + 4
8. Store Word and Decrement
swdec Rt, offset(Rs) #Mem[Reg[Rs] + sign extended offset] = Reg[Rt], Reg[Rs] = Reg[Rs] – 4
Note: Treat each new added instruction separately i.e. Each new added instruction is treated as the only one to be added to the standard datapath showing the
necessary added gates and control signals
2. Datapath Timing
Calculate the delay and the minimal clock cycle in the modified datapaths when performing each new instruction above. Assume the following delays:
Memory: 200ps
Register Files Access (READ/Write): 50ps
ALU and adders: 100ps
Logic Gates and Multiplexors: 1ps
All other times are negligible