Presenter: Jyun-Yan Li Specification-based Compaction of Directed Tests for Functional Validation of Pipelined Processors Heon-Mo Koo Intel Corporation, 1900 Prairie City Road Folsom, CA 95630, USA Prabhat Mishra Computer & Information Science & Engineering,University of Florida, Gainesville, FL 32611, USA CODES+ISSS '08 Proceedings of the 6th IEEE/ACM/IFIP international conference on Hardware/Software codesign and system synthesis

Functional validation is a major bottleneck in microprocessor design methodology. Simulation is the widely used method for functional validation using billions of random and biased-random test programs. Although directed tests require a smaller test set compared to random tests to achieve the same functional coverage goal, there is a lack of automated techniques for directed test generation. Furthermore, the number of directed tests can still be prohibitively large. This paper presents a methodology for specification-based coverage analysis and test generation. The primary contribution of this paper is a compaction technique that can drastically reduce the required number of directed test programs to achieve a coverage goal. Our experimental results using a MIPS processor and an industrial processor (e500) demonstrate more than 90% reduction in number of directed tests without sacrificing the functional coverage goal. 2

Random and biased-random test program generation is widely used  Simulation-based validation in the design cycle  Directed test generation has shorter tests in the same coverage Directed test still large  Multiple pipeline interactions reaches the target functional  Test generation after compact  This paper present FSM directed test generation 3

4 FSM model [2, 20] FSM model [2, 20] Abstraction FSM model [3, 8, 13,15, 17] Abstraction FSM model [3, 8, 13,15, 17] Model checker [10, 11] Model checker [10, 11] Produce test program Static Test compaction Architecture Description Language (ADL) [12] Architecture Description Language (ADL) [12] Specification-based Compaction of Directed Tests for Functional Validation of Pipelined Processors This paper: Remove unreachable & redundant state Complex FSM models, state explosion problem Generated from the abstract FSM Define processor’s functionalities Reduce unnecessary state

FSM modeling of pipelined processor Remove unreachable states Remove illegal transitions Remove redundancy state Test generation 5

6 Processor’s state S k : SS 1 SS 2 SS U N bits stall

Identifying unreachable states  Pass instruction to either EX1 or EX2  State: xx0100xx or xx0001xx,not xx0101xx 7 ID EX1 EX2 EX1 EX2 Idle00 Normal op.01 Stall10 Exception11

Table 1  State: xx0001xx -> xx0101xx, not xx0001xx Table 2  State: xx01xx -> xx00xx or xx01xx or xx11xx, not xx10xx Table 3  State: xx11xxxx -> xx0000xx 8 ID EXE ID EXE norm al ID norm al ID EXE exce ption idle ID EXE idle Idle00 Normal op.01 Stall10 Exception11

Inevitable state  Only one state in the next state list  Example 。 State: xx11xx -> xx00xx 。 No need state : xx01xx, xx10xx 9 MEM exce ption idle Idle00 Normal op.01 Stall10 Exception11

Coverage-driven test selection  StateCovered flag 。 Initial = 0  TransitionCovered flag 。 Initial = 0 10 ID idle oper stall IF IALU SC ns TC ps … … … … =0 =1 SCStateCovered flag TCTransitionCovered flag psPrevious state nsNext state

Multi-exception at clock cycle 7  overflow exception in IALU  divide by zero exception in DIV  memory exception in the MEM 11 Original property Negated property Decomposed into 3 sub-properties Input source Test program

12 Remove unreachable state Remove illegal state & redundancy

Functional test compaction technique to reduce test program and achieve functional coverage 3 methods for compaction  Identifying unreachable states  Identifying illegal stage transitions  Identifying inevitable state My comment  A idea for functional verification by the state FSM  How to select test program to achieve 100% state and transition coverage 13

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