EE694v - Verification - Lect 12 Lect 12,13,14 – 762 Testbenches Lets look at the EE 762 testbenches Look at stimulus generation techniques Look at response monitoring techniques EE694v - Verification - Lect 12

Pr_step1 Testbench – 4 to 1 Mux Number of inputs to design is small – only 6 inputs – input vector space is 26 = 64 Exhaustive testing used as only 64 testcases Output is checked via visual inspection of the waveform Total effort ~= effort for automation of check Design under verification is considered a “black box” – must verify from the inputs and monitor only the outputs NOTE: Still use additional indications/labels in testbench to make visual verification easier EE694v - Verification - Lect 12

EE694v - Verification - Lect 12 The waveform EE694v - Verification - Lect 12

Pr_step2 Testbench The ALU Slice Exhaustive testing is no longer a possibility. Number of inputs has grown to 15. Would need 32,768 inputs, some of which wouldn’t make sense. Choose 22 operations that the ALU slice is capable of computing and verify them for 4 inputs. 2 operations are verified for 8 inputs. Total - 96 Results are still checked visually Still ~= effort for automated checking EE694v - Verification - Lect 12

Pr_step – 8 Bit ALU Automatic Checking of Results Once you get to an 8 bit result can no longer do a visual verification of results. Number of inputs has grown to 29. Exhaustive testing would take ~539 million inputs!!! Number of input applied for testing is now 168 A separate process now monitors the outputs Expected outputs are listed in an array in the testbench. – Note the task to maintain this style of output checking. Not practical for more design efforts. EE694v - Verification - Lect 12

Pr_step – Behavioral ALU Description Using behavioral VHDL code to do description of the ALU Array of expected outputs now contain comments as to which test it represents Operation being tested and test number used to get expected result out of table – Test can be easily sequenced in a different order. Pr_step5 – testbench structure is the same – advancement to use of procedures in processes Pr_step6 – testbench structure is the same – advancement to the use of packages EE694v - Verification - Lect 12

Pr_step – Using Busses The Datapath Register Set This step advances to the use of busses for the transfer of data. There are now multiple drivers for the bus signals Procedure in testbench both applies values and checks results Bus is checked when it transitions from high-impedance (z) to the value, the value is held on the bus and then the bus returns to a value of z. Bus requires continual monitoring. EE694v - Verification - Lect 12

Pr_step8 – The Complete Datapath Need a testing plan as to what needs tested and how it will be tested. Initialize control signals (14 signals) Load initial values into registers and make sure they were loaded correctly, i.e., dump registers. Also assures that busses are working at least in part. Do basic operations using ALU(17 operations). Only the connectivity of the ALU needs verified not its full functionality. Final dump of registers EE694v - Verification - Lect 12

EE694v - Verification - Lect 12 Pr_step8 (cont) Procedures written to call bus cycle procedure for both one and two register operand operations Another procedure is used to run the bus cycle and do the results checking. Registers and functional aspects of ALU are assumed to be working for this testbench. Correct integration is checked for. Review the code. EE694v - Verification - Lect 12

Formatting Listing and Waveform A .do file is generated that provides a uniformity to the generation of the listing file and also to the waveform. A good idea is to develop such practices in your work, i.e., a format that makes it easier for you to locate that an error was found should be adopted. EE694v - Verification - Lect 12

Testing a sequential machine Free running clock of a given duty cycle May need to be checked in an industrial setting. Mixed mode system Discrete modeling of analog components EE694v - Verification - Lect 12

EE694v - Verification - Lect 12 Floating point tests Testing of Floating point execution unit. Hugh test space. Very large number of tests. Easiest A file of test inputs and expected results Each test is a “transaction” DUT responds to transaction Have reviewed textio EE694v - Verification - Lect 12