# Shared Flashcard Set

## Details

ECE327 Concepts post-midterm
Concepts for ECE327 post-midterm
107
Computer Science
04/05/2012

Term
 how to define performance?
Definition
 work/time
Term
 how can you improve performance?
Definition
 1. increase work2. decrease time
Term
 write an equation for "Big is n% greater than Small"
Definition
 1. (performance big - performance slow)/performance slow2. (time slow - time fast)/time fast
Term
 write an equation for Tavg
Definition
Term
 In order to optimize, what are two things that needs to be taken account?
Definition
 run time and frequency of occurence
Term
 what's a general rule to improve performance?
Definition
 make the common case faster
Term
 give an equation for time
Definition
 cycle * clockPeriod = numInstr*CPI*clockPeriod
Term
 What is CPI?
Definition
 cycle per instruction
Term
 what does SPECint measure?
Definition
 measures performance
Term
 if performance increase by 3 time every 12 months, give an equation of performance at t month
Definition
 P(t) = p(0)*3^(t/t0)
Term
 What is functional validation?
Definition
 right behavior?
Term
 What is functional verification?
Definition
 behavior is right?
Term
 What is formal verification?
Definition
 functional verification for every possible inputs
Term
 What is performance validation?
Definition
 right performance?
Term
 What is power validation?
Definition
 right power?
Term
 What is equivalence verification?
Definition
 design generated by synthesis tool has same behavior as RTL code?
Term
 what is timing verification?
Definition
 all paths meet time constraints?
Term
 What is coverage?
Definition
 % of cases covered
Term
 if we have n bits of inputs and k bits of flops, how many different cases when doing functional verification?
Definition
 2^(n+k) cases
Term
 What are two characteristics for test bench?
Definition
 1. no inputs or outputs2. test bench only used for primary input and output
Term
 When to use assertions?
Definition
 when check behavior of internal signals
Term
 What is DUT in test bench?
Definition
 circuit that you are checking
Term
 What is stimulus in test bench?
Definition
 generates test vectors
Term
 What is specification in test bench?
Definition
 describes desired behavior of implementation
Term
 What is check in test bench?
Definition
 checks whether implementation obeys specification
Term
 Draw a diagram for a normal test bench
Definition
Term
 Draw a diagram for reference model test bench
Definition
Term
 When are reference model test bench used?
Definition
 check if output has a specific valuee.g DSP filters, instruction decoder, datapath
Term
 Draw a diagram for relational test bench
Definition
Term
 When are relational test bench used?
Definition
 based on relationship of input and outpute.g carry-save adders, control circuits
Term
 Datapath circuits are suitable for what kind of test bench? What about control circuits?
Definition
 Datapath = referenceControl = relational
Term
 Why control circuits are often more challenging to verify?
Definition
 1. has internal signals which test bench can't check2. bugs can exists in any clock cycle and test bench doesn't know which cycle the bug is at
Term
 How to resolve the issue of bug at certain clock cycle?
Definition
 use queue
Term
 What is the goal of coverage monitor
Definition
 certain event is exercised in a simulation run or not
Term
 What's the pro and con of using function in VHDL?
Definition
 Pro: flexiblecon: verbose
Term
 What is clock skew?
Definition
 the difference in arrival times for the same clock edge at different flop
Term
 what is clock latency?
Definition
 difference in arrival times for the same clock edge at different levels of interconnect along the clock treeclock latency doesn't affect the limit on minimum clock eriod
Term
 what is clock jitter?
Definition
 difference between actual clock period and ideal clock period
Term
 what are 2 causes of clock jitter?
Definition
 1) tmp and voltage variations over time2) different manufacturer
Term
 What is the difference between behavior of flop and latch?
Definition
 flop is edge sensitive and latch is level sensitive
Term
 When does setup time occur?
Definition
 just before the edge
Term
 When does hold time occur?
Definition
 just after the edge
Term
 What is clock-to-Q time?
Definition
 delay from the clock edge to when the output is guaranteed to be stable
Term
 What is propagation delay?
Definition
 time it takes a signal to travel from the source flop to destination flop
Term
 What's the equation for propagation delay?
Definition
Term
Definition
 combinational gates between the flops
Term
 what is interconnect delay?
Definition
 wires between gates and flops
Term
 that's the equation for clock period?
Definition
 clockP > skew + jitter + Tco + propagation + setup
Term
 is the equation for clock period independent of hold time?
Definition
 yes
Term
 what's the equation for hold constraint?
Definition
 skew + jitter + Tho < Tco + prop
Term
 when does setup violation occur?
Definition
 clock-to-Q + prop delay is too big
Term
 when does hold violation occur?
Definition
 before hold time ends, data changes
Term
 what 3 things needs to be identified to calculate setup and hold time?
Definition
 1. how data is stored when not connected to input2. the gates that the clock uses to cause the stored data to drive the output3. the gates that the clock uses to cause the input to drive the output
Term
 when does setup start? when does it end?
Definition
 start: when data start to propagateend: when data finish to propagate
Term
 when can data, w/a, occur?
Definition
 at t=0, input has w and output has athen at t=1, output will have w/a
Term
 when does hold start? when does it end?
Definition
 start: when data start to enter key gateend: when the other data start to enter key gate
Term
 what's common about start and end of hold time and setup time?
Definition
 start: there is a key gate which one of the signal starts to enterend:both signals enter key gate
Term
 what's critical path
Definition
 the slowest path on the chip between flops or flops and pins.
Term
 what's the effect of critical path
Definition
 limits max clock period
Term
 what's false path
Definition
 change in input doesn't affect change in output.makes people believe they are critical path, but in reality, it's not a critical path
Term
 what's an algorithm to determine the critical path?
Definition
 1. find longest path ignoring false path2. test if the path is false path or not3. choose next longest path if it's false path4. do a correct, complete, and complex algorithm to find the critical path in a circuit
Term
 need to put rest of the questions after understanding rest of chapter 5
Definition
Term
 what's the equation for energy?
Definition
 v*c
Term
 what's the equation for power given v and i?
Definition
 v*i=energy/time
Term
Definition
 heat
Term
Definition
 battery life or energy costs
Term
 what's equation for "power efficiency"?
Definition
 MIPs/watts
Term
 how to calculate energy given v and AH?
Definition
 convert hour to second, keep in mind ampere is in I/s
Term
 clock speed is proportional to what?
Definition
 power
Term
 what is the equation for power for hardware?
Definition
 switch power + short power + leakage power
Term
 how much energy is needed to charge a capacitor?
Definition
 c*v^2
Term
 what's the charged energy on a capacitor?
Definition
 0.5*c*v^2
Term
 what's f'?
Definition
 frequency at which inverter goes through complete charge-discharge cycle
Term
 what's activity factor?
Definition
 average number of times the signal switches from 0->1 or 1->0 per clock cycle
Term
 what's f'?
Definition
 0.5*activity factor*clock speed
Term
 what's average switching power in terms of f'?
Definition
 f' * energy needed to charge capacitor to v
Term
 what's equation for short circuit power?
Definition
 activity factor * clock speed * timeshort * power needed to store to capacitor
Term
 what's leakage power?
Definition
 Ileak * volt
Term
 what's leakage current proportional to?
Definition
 exp[(-q*voltThresh)/(k*T)]
Term
 what two categories you can divide power reduction to?
Definition
 analog and digital
Term
 what are parameters to reduce power in analog level?
Definition
 capacitance, resistance, voltage
Term
 what are parameters to reduce power in digital level?
Definition
 capacitance, activity factor, clock frequency
Term
 what are 5 techniques for reducing power in analog level?
Definition
 dual-VDD, dual-Vt, exotic circuits, adiabatic circuits, clock trees
Term
 what are 5 techniques for reducing power in digital level?
Definition
 multiple clocks, clock gating, data encoding, glitch reduction, asynchronous circuits
Term
 what is dual-VDD power reduction technique?
Definition
 two different supply voltages. High voltage for performance-critical portions for design, low voltage for remainder of the circuit
Term
 what is dual-Vt power reduction technique?
Definition
 two different threshold voltages. low threshold voltage for high performance, high threshold voltage for low performance
Term
 what's exotic circuits in power reduction technique?
Definition
 special circuits that run high frequency while minimizing power
Term
 what's adiabatic circuits in power reduction technique?
Definition
 special circuits that consumes power on 0->1 transitions but not 1->0 transitions. Bad thing is this sacrifices performance
Term
 what's clock trees in power reduction technique?
Definition
 up to 30% of total power can be consumed in clock generation and clock tree
Term
 what's multiple clocks in power reduction technique?
Definition
 high speed clock in high performance circuit, low speed close for remainder of circuit
Term
 what's clock gating in power reduction technique?
Definition
 turn off portion of clock when not needed
Term
 what's data encoding in power reduction technique?
Definition
 gray coding vs one-hot vs fulling encoded
Term
 what's glitch reduction in power reduction technique?
Definition
 reduce glitches
Term
 what's asynchronous circuits in power reduction technique?
Definition
 get rid of clocks
Term
 what's power proportional to for hardware?
Definition
 v^2
Term
 what will happen to hardware when we increase the supply voltage?
Definition
 decrease delay through a circuit
Term
 what's max clock speed proportional to in terms of Vsupply and Vthresh?
Definition
 (Vsup - Vthresh)^2/Vsup
Term
 what will happen to Ileak as Vthresh is decreased?
Definition
 Ileak will increase
Term
 what is power proportional to in terms of Ileak?
Definition
 Ileak
Term
 what's effectiveness of clock gating?
Definition
 % of time there is invalid data, clock if off
Term
 what's %valid for clock gating?
Definition
 % of clock cycles with valid data in circuit the clock must be toggling
Term
 what's %clk for clock gating?
Definition
 percentage of clock cycles that clock toggles
Term
 what's equation for effectiveness of clock gating?
Definition
 %clkOff/%invalid
Term
 what happens to effectiveness of clock gating if clock toggles only when there is valid data?
Definition
 effectiveness = 100%
Term
 what happens to effectiveness of clock gating if clock always toggles?
Definition
 effectiveness = 0%
Term
 in clock gating, what happens if %clk < %valid?
Definition
 turning off clock when shouldn't
Term
 what's the new activity factor given clock gating?
Definition
 A - (1-%valid)*Eff*A
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