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Digital Questions

Basics

  • What is sequential vs combinational logic?
  • Design a circuit that can detect a low to high edge for one clock cycle using only one FF and gates.
  • Make an OR gate using 2-1 muxes
  • Make a mux using gates
  • Types of FSMs:
    • One-hot
    • Output encoded
    • Fully encoded
  • Explain the difference between a Mealy and Moore machine
  • Design a latch
  • Design XOR gate using 2:1 MUX solution

Circuits

  • Know how to convert an FSM into a digital circuit
  • Design an adder

Timing

  • Explain the following:
    • T_setup
    • T_hold
    • T_clk2q
    • T_prop
  • What is clock skew and what problems can it cause? How do you account for it?
  • What is a PLL?
  • What are waveform viewers, and why do we use them?

Applications

  • Explain how a USB system works, including:
    • Protocols
    • Bitstuffing
    • NRZI
    • DPDM
    • Difference between USB 2 and 3 (and USB-C!)
  • Generally know how to implement memory in digital circuits
  • Describe different steps in an ethernet protocol, e.g. packet scrambling, headers, etc.
  • Describe how you would implement SHA-256 (or maybe a simpler crypto algorithm)
  • Describe how TCP/UDP works

FPGAs

  • What is an FPGA?

    • How is it constructed?
    • Why are FPGAs useful?
    • Why would we use an FPGA over an ASIC or over a computer?

  • What are some of the main components that make up an FPGA and why are they useful?

    • LUTs
    • FFs
    • DRAM, BRAM, URAM
    • DSPs
    • PCIe
    • Transcievers

  • What is a High-Speed Gigabit Transciever on an FPGA?

    • Why is this necessary or important?
    • How does it interact with PCS/PMA/MAC?

  • How does an FPGA implement a function?

    • How do LUTs work?

  • What are the different ways to store memory on an FPGA?

    • FFs vs. LUTs vs. RAM

  • What are the necessary steps to go from RTL code to FPGA bitstream?

  • How might the FPGA interact with host (CPU)?

    • describe DMA and PCIe
    • describe NIC and ethernet packets

  • What are Bus Funtional Models (BFMs) and how do they help with FPGA design verification?

  • What are the differences between simulation and emulation (on-board/silicon)?

  • What are some of the main tools FPGA engineers use today?

    • Simulation
    • Verification
    • Emulation
    • Network Debugging

  • Describe CLBs and how they relate to LUTs and FFs on an FPGA

  • Describe ways to send stimulus (signals, packets, memory writes, etc) to a simulation RTL for verification purposes

    • Testbenches in SystemVerilog
    • C++ using SystemC library

System Verilog

  • Difference between blocking and nonblocking statements
  • What is the difference between rand and randc

FSM Design

  • Design a traffic light FSM, that takes care of W-E, N-S intersection, with Red, Yellow and Green lights
  • Design the FSM for a vending machine that takes nickels, quarters and dimes, dispenses water bottles for $1, and gives change if the amount given is over, but does nothing if the amount of money is not enough.

Coding

  • Code a class for a Queue
  • Write a module that computes the Fibonacci numbers

Resources