Verifying Performance of a HDL design block Chhavi Patni Maninder Singh

Agenda Objective Performance parameters Application Scenario 1 Bus Probes Application Scenario 2 Conclusions

Objective Verification and Analysis of performance parameters of a Design Block Data Bandwidth Latency Efficiency Pipeline Protocol specific parameters Bus interface plugs requirement DUV

Performance Parameters Bandwidth : Rate of data transfer. Usually specified as KB/s, MB/s or Mb/s. Theoretical maximum bandwidth = (Data width) x (Bus Freq.) Actual Bandwidth = Amount of data transferred / Total clock cycles Example: Clock Freq: 200 MHz , Data Bus: 4 bytes Theoretical Max Bandwidth = 200 x 4 = 800 MB/s Efficiency : number of clock cycles transferring data divided by the total number of clock cycles. Efficiency (%) = Clock cycles transferring data Total Clock cycles x 100

Performance Parameters cont. Latency Requirements : Requests should be granted within certain cycles Request to response latency. Pipeline Features: Max. or Average Pending request transfers Protocol specific parameters : DDR Bus : bank BW analysis, ACT / PRECHARGE with no read/write cycles Bus Interface plugs requirements : Capable of accepting back to back requests. Capable of providing back to back responses.

Application Scenario 1 Cache IP Functional Specifications : Bandwidth Supported : Allegro streams : Max / Avg BW (MB/s) = 809 / 487 DVD streams : Max / Avg BW (MB/s) = 474 / 245 Efficiency : Reduction in number of Memory accesses = 30% Other requirements : request can be read every clock cycle data can be sent by IP every clock cycle

Verification Environment Reference Model checker checker Initiator BFM Target BFM Cache IP Bus Probe

Bus Probe Internal tool - Bus probes – on STBus, AXI, DDR3 "Probes" are transaction monitors, that observe the transitions of RTL signals, recognize transactions and record them in a transaction database Purpose : Monitor for Bus protocol compliance. Provides all transactions for scoreboarding/checking. Provides summary of transaction types along with start and end time for analysis. Provides latency, bandwidth figures.

Bus Probe Non-intrusive probing of the simulation Usage : A probing file defines each probe and the paths of the signals to monitor Usage : Static Mode: Need vcd/ shm database of simulation. Dynamic Mode: Reports generated on the fly during simulation run. Axi_probe <probe_name> .data_size(_value_of_attribute_data_size_) .*("_common_path_and_signal_root_*_suffix_") …….. OR .data_size((_value_of_attribute_data_size_) .AWVALID(“testbench.awvalid") .AWREADY(CONSTANT(1)) …………

Bus Probe Output Example Output :

Application Scenario 2 DDR Traffic Sequencer SoC Traffic BFM #N Model BW, η, Latency SoC Traffic Sequencer RTL Sequencer Architecture Model BFM #N #3 Memory #2 Traffic Generator #1 RTL BW, η, Latency Bus Probe

Conclusions Performance Verification of IP Performance Analysis of architecture models RTL v/s Architecture Model Comparison Tuning third Party IP for maximum performance

DDR Probe Efficiency of the memory Bank access analysis Compute the percentage of the maximum available bandwidth that is actually used by the DDR. global bandwidth, read / write bandwidth bandwidth per bank, read bandwidth per bank, write bandwidth per bank Bank access analysis number of pages accessed in each bank (different row addresses) number of ACT commands per bank Bus turnarounds Bus turnarounds between read transactions and write transactions, or the opposite. Sub-optimal usage of the memory banks ACT followed by a PRE on the same bank, without READ nor WRITE transactions continuous use of a single bank (as the efficient usage of the ddr is based on alternate bank accesses)