EE434ASIC & Digital Systems Jacob Murray School of EECS Washington State University email@example.com
Test Methodologies Lecture 32
Conceptual Architecture of Core Test • Three separate elements in the embedded core test infrastructure. • Test pattern source and sink • Test Access Mechanism • Core test wrapper
Implementation of TAM • When implementing a TAM, we have the following options • A TAM can either reuse existing functionality to transport test patterns or be formed by dedicated test access hardware. • A TAM can either go through other modules on the IC or pass around those other modules. • One can either have an independent access mechanism per core, or share an access mechanism with multiple cores. • A test access mechanism can either be a plain signal transport medium, or may contain certain intelligent test control functions.
Reuse of Boundary scan test • A scan chain around embedded cores. • It provides access for the core-internal tests as well as intercore interconnect testing. • Boundary scan test has the advantage that it builds on an existing method. • Drawback: Single bit for test control and test data access path, does not allow trade off between bandwidth and test time.
Test Rail • Combines the strength of both the test bus and boundary scan test approaches. • One or more test rails of varying width per IC – trade off between test time and silicon area. • Multiple cores can be daisy chained into one test rail. • Per core there is a test rail bypass-allows user to test each core sequentially or multiple cores in parallel – trade off between diagnostic resolution and test time.
Test Rail (cont’d.) • Capable of transporting test stimuli and responses for synchronous digital tests • Test Rail width relates to following: • Host pins • Test time • Silicon area • Number of host pins available to accommodate test signals is given
Wrapper • Interface between the embedded core and its system chip environment. • It connects the core terminals both to the rest of the IC, as well as to the TAM. • It is implemented on chip.
Test Shell: An Example of Wrapper • Three levels of hierarchy • IP module • Test Shell • Host • IP module is the actual reusable core • Test Shell is the wrapper of the core • Host is the SOC environment in which the core is embedded
Host - Test Shell Interface (cont’d.) The interface between host and Test Shell consists of three types of input/output terminals: • Functional inputs/outputs: - these are the normal inputs/outputs of the IP module • Test Rail inputs/outputs: - handles the test data transport for all synchronous digital tests • Direct test inputs/outputs: - only non-synchronous or non-digital test signals
Test Shell - Control Mechanism • The TCM is meant to control the operation of the Test Shell • Two types of test control signals exist: • Pseudo-static test control signals - these signals set up the conditions for a certain test (e.g. IEEE 1149.1 type signals) • Dynamic test control signal like scan-enable
Wrapper Standardization - P1500 • TAM Source/Sink • From chip I/O and from test bus, test rail, BIST, etc. • TAM In/Out • 0 to n lines for parallel and/or serial test data, or test control • Standard P1500 Serial Access & Control • From chip-level TAP controller, chip I/O, etc.
P1500 Wrapper Instruction RegisterProposed Required Instructions • Normal • Wrapper cells allow normal core inputs/outputs to pass through the wrapper for normal system operation • Core Test • Wrapper cells are configured to disable the core’s normal mode & connected to TAM and/or wrapper serial input/output for core test • Sources & sinks, and core test methods are user defined • Serial External Test • Wrapper cells are configured to disable the core’s normal mode, and are connected serially between the wrapper serial input/output • Isolation • Wrapper cells are configured to disable the core’s normal mode, and enable setting of appropriate core inputs or outputs to constrained and/or disabled values for core isolation
P1500 Wrapper Registers • Standard P1500 protocol for Wrapper Registers will provide for: • Parallel capture of input data into the selected register • Serial shift of the register from serial input to serial output • Update scan-in data of register to a parallel update stage • Required for Wrapper Instruction Register and optional for others
P1500 Wrapper RegistersStandard Serial Scan Path Configuration • Serial Control lines enable & perform scan, and select between: • Wrapper Instruction Register (WIR) • Or other Data Registers (DRs), e.g. Wrapper Cell Register, Bypass, etc. • Updated WIR then selects between DRs
P1500 Wrapper Interface Port(WIP) • WIP is used to access the WIR,Bypass and other data registers
Example of application cf. IEEE P1500 Standard
Example of application (serial intest) cf. IEEE P1500 Standard
Example of application (bypass) cf. IEEE P1500 Standard
Example of application (serial extest) cf. IEEE P1500 Standard
Example of application (parallel extest, intest) cf. IEEE P1500 Standard
P1500 Wrapper Cell ExampleDedicated Output Cell with Update Stage & TAM-Out
P1500 Wrapper Cell ExampleDedicated Input Cell with Update Stage & TAM-In
Test control of multiple cores • Control signals are common to each core • scheduling of core test • control signals are applied accordingly • some kind of control mechanism either through a system FSM, embedded system controller or even external control from ATE