Design Verification at D2Audio


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Design Verification at D2Audio

  1. 1. Design Verification at D2Audio March 8, 2006 Mayur Mehta1
  2. 2. D2Audio Products • D2Audio builds all Digital Class D amplifier controller ICs which use sophisticated digital Pulse Width Modulation (PWM) Techniques. All-digital signal path On-Chip DSP provides amplifier controls and comprehensive audio signal processing. 25-600 watts per channel 93% power efficient2
  3. 3. D2Audio Products – Enabling Digital Power In The Broad Audio Market Consumer Professional Automotive3
  4. 4. D2Audio Integrates Multiple Functions in IC Amplifier GUI DSP Digital I /O VID1___ Firmware VID2___ AUD___ HDMI__ S/PDIF_ Tuner__4
  5. 5. ONLY True “Scalable” Solution from 15W to 600W Today! Assumed Performance Constraints • 8-ohm Loudspeaker • < 0.1% Distortion • > 100dB SNR D2Audio 150W+ • Reliable and Cost-Effective Intelligent Discrete Discrete PWM Controller Driver N+N FETs D2Audio 125W Intelligent Discrete Discrete PWM Controller Driver N+P FETs Power Level (8 ohm) Technology-Imposed Limit Integrated Discrete 75W Controller Driver FETs • 40V Process Limit • Protection • Control Integrated • Drive 50W Controller Power Stage PWM controller Drive/Protection/Power5
  6. 6. Verification Overview6
  7. 7. Chips Developed • 1st Gen Digital Audio Engine IC (DAE-1) PWM Controller with SRC (Sample Rate Converter), DSP, Output Protection In production for > 1year • Demonstrated full audio performance and features on first silicon. • 2nd Gen Digital Audio Engine IC (DAE-2) First to develop Class D amplifier with all-digital feedback • Power supply feed-forward and closed-loop feedback technology correct for power supply variations, non-linearity and other distortion-inducing mechanisms • As much as 60dB performance improvement • Most analog PWM Solutions use analog closed-loop feedback In Production Now • Demonstrated full audio performance with feed forward and feedback on first silicon • 4 channel and 7 channel reference design solutions7
  8. 8. Chip Block Diagram !! ! % ! # ! # " ! ! ) & ! " % ( * $8
  9. 9. Verification Techniques • C++ Model • Verilog simulations Block-level and chip-level verification NC-Verilog, Verdi and SureCov CVS, Bugzilla and nLint Verilog level transactors interacting with embedded C Program to synchronize DSP and I/O functions Assembly level and C code to perform DSP functions • FPGA emulation Full chip implementation synthesized to Xilinx FPGA Custom I/O boards developed for “rest of system” Connectivity to real world audio streams Back-end power electronics for amplifier system testing9
  10. 10. Development and Verification Flow for Signal Processing Blocks • Matlab – Numerical Analysis tool to aid in developing algorithms • C++ based simulator • Matlab script generates a setup file and input data files Executes the C++ simulator and dumps output into files. On termination of simulator, Matlab script performs analysis of the data produced by simulator. • C++ model to implement algorithms on a fairly high level Verify the functionality using the above C++ simulator Determine gross computational complexity • Refine the algorithms to a cycle accurate level10
  11. 11. Development and Verification Flow11
  12. 12. Development and Verification Flow (Contd.) • Verification environment Generate setup files, input and expected output data for the RTL Simulator. Verilog based transactor performs RTL initialization, initializes the computational engine and runs the simulation with input data while it compares output data to the expected data read from files. Run Verilog simulations with the cycle accurate model in parallel to verify that the RTL implementation has same functionality and identical performance to the original model. • Run extensive simulations to exercise typical setups as well as the boundaries of the design. • Typically the output files from Matlab become part of the design data base Test Suites for regression testing • Maintain C++ model to match architectural and design changes12
  13. 13. Block Diagram of Chip-level Verification Global Transactor Transactor Transactor PUMPLO PSSYNC OSCOUT PUMPHI XTALO SRD0 SRD1 SCK0 SCK1 XTALI STD0 STD1 SC0 SC1 TIO 3 3 3 2 SDIN Reserved Serial Audio Interface 2 PLL Timer SCKR Serial Audio Interface Transactor 2 LRCLK MCLK SCLKT LRCKT Digital Signal Processor Pulse Width Modulator SDOUT SCLK PWMH0 Frequency Response Correction RXD SCI Sample Rate Conversion PWML0 Transactor TXD PWMH1 Transactor Linear Interpolator PWM Correction PWML1 Noise Shaper Output Drive SCL Quantizer 2-Wire Effects PWMH2 SDA PWML2 SPDIFRX PWMH3 S/PDIF PWML3 SPDIFTX nRESET OTSEL Control nRSTOUT Transactor PWMSYNC 5 SYS 4 BMS 8 GPIO 16 TEST Power Supply Protection XGPIO 4 4 4 PROTECTC PROTECTA PROTECTB PLLAVDD PLLAGND PLLDVDD PLLDGND OSCVDD PWMVDD PWMGND CVDD CGND RVDD RGND nTRST TEST Test.c Test.V Transactor13
  14. 14. Verification Techniques – FPGA Emulation •1:1 Mapping with the chip •Capability to do performance correlation •Verify external Interfaces •Platform for software development •Vehicle to demonstrate performance and new FPGA Emulation System features14
  15. 15. Lessons Learned • Always Emulate Bug count found in FPGA emulation easily justifies effort and resources expended Confidence of working with real world interfaces without surprises Great tool to develop software which allows us to accelerate firmware development Emulation system should be scalable, repeatable and transportable • Top-level environment where tests can be interchangeably simulated and emulated is very valuable. Needed to debug emulation system during bring up stages FPGA was always correlated with RTL FPGA emulation is used as a hardware accelerator15
  16. 16. Lessons Learned (Contd.) • Code Coverage was useful in finding holes in our test cases • Project Management Comprehensive Microsoft Project scheduling with detailed dependencies between RTL Development, Block-level verification,Chip verification, FPGA and Physical design completion16
  17. 17. Why the current methodology works for D2Audio • Comprehensive block-level and system-level specifications • Easy to use test environment allowed us to generate comprehensive tests • Everything under CVS control • Production firmware was run on FPGA emulation before tape-out • Comprehensive verification in simulation environment before starting FPGA Verification • FPGA emulation confirmed performance before tape-out Confirms that the high-level model represents reality Plug tests • Simple verification environment allowed us to scale verification resources • Mature engineering team17
  18. 18. Improvements • Plan to use assertion tools for debugging, verification and Code/functional coverage • Add regression suite for FPGA builds • Evaluate System C/System Verilog Improve inefficiencies in the current verification environment • Test Development • CPU intensive • Verify external IP for complete functionality and clear specifications18
  19. 19. Suggested Follow-up activities of DVClub • Present a methodology which has used assertion tools • Present a methodology which has used code and functional coverage tools Correlation with bugs found on chip How do you use it to predict schedule and tape-out decision • Discuss Verification projects which did not use FPGA emulation • Discuss projects which developed software simulator of a chip for partners to use for software development • DV for mixed signal ICs • Pros and Cons of outsourcing verification19