Built-in self-test
Encyclopedia
A built-in self-test or built-in test (BIT) is a mechanism that permits a machine to test itself. Engineers design BISTs to meet requirements such as:
or constraints such as:
BIST is commonplace in weapon
s, avionics
, medical device
s, automotive electronics
, complex machinery of all types, unattended machinery of all types, and integrated circuit
s.
s, which are then removed and repaired elsewhere, usually in depots or at the manufacturer. Commercial aircraft only make money when they fly, so they use BIST to minimize the time on the ground needed for repair and to increase the level of safety of the system which contains BIST. Similar arguments apply to military aircraft. When BIST is used in flight, a fault causes the system to switch to an alternative mode or equipment that still operates. Critical flight equipment is normally duplicated, or redundant. Less critical flight equipment, such as entertainment systems, might have a "limp mode" that provides some functions.
(POST) will perform a comprehensive test. Then, a periodic test will assure that the device has not become unsafe since the power-on self test. Safety-critical devices normally define a "safety interval", a period of time too short for injury to occur. The self test of the most critical functions normally is completed at least once per safety interval. The periodic test is normally a subset of the power-on self test.
) because it's a very complex piece of machinery. Since it includes a computer, a computerized self-test was an obvious, inexpensive feature. Most modern computers, including embedded system
s, have self-tests of their computer, memory and software.
. For example, power systems or batteries are often under stress, and can easily overheat or fail. So, they are often tested.
Often the communication test is a critical item in a remote system. One of the most common, and unsung unattended system is the humble telephone concentrator box. This contains complex electronics to accumulate telephone lines or data and route it to a central switch. Telephone concentrators test for communications continuously, by verifying the presence of periodic data patterns called frames (See SONET
). Frames repeat about 8,000 times per second.
Remote systems often have tests to loop-back the communications locally, to test transmitter and receiver, and remotely, to test the communication link without using the computer or software at the remote unit. Where electronic loop-backs are absent, the software usually provides the facility. For example, IP
defines a local address which is a software loopback (IP-Address 127.0.0.1, usually locally mapped to name "localhost").
Many remote systems have automatic reset features to restart their remote computers. These can be triggered by lack of communications, improper software operation or other critical events. Satellites have automatic reset, and add automatic restart systems for power and attitude control, as well.
s, BIST is used to make faster, less-expensive manufacturing tests. The IC has a function that verifies all or a portion of the internal functionality of the IC. In some cases, this is valuable to customers, as well. For example, a BIST mechanism is provided in advanced fieldbus
systems to verify functionality. At a high level this can be viewed similar to the PC BIOS
's power-on self-test (POST) that performs a self-test of the RAM
and buses on power-up.
The main purpose of BIST is to reduce the complexity, and thereby decrease the cost and reduce reliance upon external (pattern-programmed) test equipment. BIST reduces cost in two ways:
Both lead to a reduction in hourly charges for automated test equipment (ATE) service.
The BIST name and concept originated with the idea of including a pseudorandom number generator
(PRNG) and cyclic redundancy check
(CRC) on the IC. If all the registers that hold state in an IC are on one or more internal scan chains, then the function of the registers and the combinational logic
between them will generate a unique CRC signature over a large enough sample of random inputs. So all an IC need do is store the expected CRC signature and test for it after a large enough sample set from the PRNG. The CRC comparison with expected signature or the actual resultant CRC signature is typically accessed via the JTAG IEEE
1149.1 standard.
There are several specialized versions of BIST which are differentiated according to what they do or how they are implemented:
- high reliabilityReliability engineeringReliability engineering is an engineering field, that deals with the study, evaluation, and life-cycle management of reliability: the ability of a system or component to perform its required functions under stated conditions for a specified period of time. It is often measured as a probability of...
- lower repair cycle times
or constraints such as:
- limited technician accessibility
- cost of testing during manufacture
BIST is commonplace in weapon
Weapon
A weapon, arm, or armament is a tool or instrument used with the aim of causing damage or harm to living beings or artificial structures or systems...
s, avionics
Avionics
Avionics are electronic systems used on aircraft, artificial satellites and spacecraft.Avionic systems include communications, navigation, the display and management of multiple systems and the hundreds of systems that are fitted to aircraft to meet individual roles...
, medical device
Medical device
A medical device is a product which is used for medical purposes in patients, in diagnosis, therapy or surgery . Whereas medicinal products achieve their principal action by pharmacological, metabolic or immunological means. Medical devices act by other means like physical, mechanical, thermal,...
s, automotive electronics
Automobile
An automobile, autocar, motor car or car is a wheeled motor vehicle used for transporting passengers, which also carries its own engine or motor...
, complex machinery of all types, unattended machinery of all types, and integrated circuit
Integrated circuit
An integrated circuit or monolithic integrated circuit is an electronic circuit manufactured by the patterned diffusion of trace elements into the surface of a thin substrate of semiconductor material...
s.
Weapons
One of the first computer-controlled BIST systems was in the U.S.'s Minuteman Missile. Using an internal computer to control the testing reduced the weight of cables and connectors for testing. The Minuteman was one of the first major weapons systems to field a permanently installed computer-controlled self-test.Avionics
Almost all avionics now incorporate BIST. In avionics, the purpose is to isolate failing line-replaceable unitLine-replaceable unit
A line-replaceable unit is a modular component of an airplane, ship or spacecraft that is designed to be replaced quickly at an operating location. An LRU is usually a sealed unit such as a radio or other auxiliary equipment...
s, which are then removed and repaired elsewhere, usually in depots or at the manufacturer. Commercial aircraft only make money when they fly, so they use BIST to minimize the time on the ground needed for repair and to increase the level of safety of the system which contains BIST. Similar arguments apply to military aircraft. When BIST is used in flight, a fault causes the system to switch to an alternative mode or equipment that still operates. Critical flight equipment is normally duplicated, or redundant. Less critical flight equipment, such as entertainment systems, might have a "limp mode" that provides some functions.
Safety-critical devices
Medical devices test themselves to assure their continued safety. Normally there are two tests. A power-on self-testPower-on self-test
Power-On Self-Test refers to routines run immediately after power is applied, by nearly all electronic devices. Perhaps the most widely-known usage pertains to computing devices...
(POST) will perform a comprehensive test. Then, a periodic test will assure that the device has not become unsafe since the power-on self test. Safety-critical devices normally define a "safety interval", a period of time too short for injury to occur. The self test of the most critical functions normally is completed at least once per safety interval. The periodic test is normally a subset of the power-on self test.
Automotive use
Automotive tests itself to enhance safety and reliability. For example, most vehicles with antilock brakes test them once per safety interval. If the antilock brake system has a broken wire or other fault, the brake system reverts to operating as a normal brake system. Most automotive engine controllers incorporate a "limp mode" for each sensor, so that the engine will continue to operate if the sensor or its wiring fails. Another, more trivial example of a limp mode is that some cars test door switches, and automatically turn lights on using seat-belt occupancy sensors if the door switches fail.Computers
The typical personal computer tests itself at start-up (called POSTPower-on self-test
Power-On Self-Test refers to routines run immediately after power is applied, by nearly all electronic devices. Perhaps the most widely-known usage pertains to computing devices...
) because it's a very complex piece of machinery. Since it includes a computer, a computerized self-test was an obvious, inexpensive feature. Most modern computers, including embedded system
Embedded system
An embedded system is a computer system designed for specific control functions within a larger system. often with real-time computing constraints. It is embedded as part of a complete device often including hardware and mechanical parts. By contrast, a general-purpose computer, such as a personal...
s, have self-tests of their computer, memory and software.
Unattended machinery
Unattended machinery performs self-tests to discover whether it needs maintenance or repair. Typical tests are for temperature, humidity, bad communications, burglars, or a bad power supplyPower supply
A power supply is a device that supplies electrical energy to one or more electric loads. The term is most commonly applied to devices that convert one form of electrical energy to another, though it may also refer to devices that convert another form of energy to electrical energy...
. For example, power systems or batteries are often under stress, and can easily overheat or fail. So, they are often tested.
Often the communication test is a critical item in a remote system. One of the most common, and unsung unattended system is the humble telephone concentrator box. This contains complex electronics to accumulate telephone lines or data and route it to a central switch. Telephone concentrators test for communications continuously, by verifying the presence of periodic data patterns called frames (See SONET
Sonet
Sonet may refer to:* Sonet Records, European record label* Synchronous optical networking * Saab Sonett...
). Frames repeat about 8,000 times per second.
Remote systems often have tests to loop-back the communications locally, to test transmitter and receiver, and remotely, to test the communication link without using the computer or software at the remote unit. Where electronic loop-backs are absent, the software usually provides the facility. For example, IP
Internet Protocol
The Internet Protocol is the principal communications protocol used for relaying datagrams across an internetwork using the Internet Protocol Suite...
defines a local address which is a software loopback (IP-Address 127.0.0.1, usually locally mapped to name "localhost").
Many remote systems have automatic reset features to restart their remote computers. These can be triggered by lack of communications, improper software operation or other critical events. Satellites have automatic reset, and add automatic restart systems for power and attitude control, as well.
Integrated circuits
In integrated circuitIntegrated circuit
An integrated circuit or monolithic integrated circuit is an electronic circuit manufactured by the patterned diffusion of trace elements into the surface of a thin substrate of semiconductor material...
s, BIST is used to make faster, less-expensive manufacturing tests. The IC has a function that verifies all or a portion of the internal functionality of the IC. In some cases, this is valuable to customers, as well. For example, a BIST mechanism is provided in advanced fieldbus
Fieldbus
Fieldbus is the name of a family of industrial computer network protocols used for real-time distributed control, now standardized as IEC 61158....
systems to verify functionality. At a high level this can be viewed similar to the PC BIOS
BIOS
In IBM PC compatible computers, the basic input/output system , also known as the System BIOS or ROM BIOS , is a de facto standard defining a firmware interface....
's power-on self-test (POST) that performs a self-test of the RAM
Random-access memory
Random access memory is a form of computer data storage. Today, it takes the form of integrated circuits that allow stored data to be accessed in any order with a worst case performance of constant time. Strictly speaking, modern types of DRAM are therefore not random access, as data is read in...
and buses on power-up.
The main purpose of BIST is to reduce the complexity, and thereby decrease the cost and reduce reliance upon external (pattern-programmed) test equipment. BIST reduces cost in two ways:
- reduces test-cycle duration
- reduces the complexity of the test/probe setup, by reducing the number of I/O signals that must be driven/examined under tester control.
Both lead to a reduction in hourly charges for automated test equipment (ATE) service.
The BIST name and concept originated with the idea of including a pseudorandom number generator
Pseudorandom number generator
A pseudorandom number generator , also known as a deterministic random bit generator , is an algorithm for generating a sequence of numbers that approximates the properties of random numbers...
(PRNG) and cyclic redundancy check
Cyclic redundancy check
A cyclic redundancy check is an error-detecting code commonly used in digital networks and storage devices to detect accidental changes to raw data...
(CRC) on the IC. If all the registers that hold state in an IC are on one or more internal scan chains, then the function of the registers and the combinational logic
Combinational logic
In digital circuit theory, combinational logic is a type of digital logic which is implemented by boolean circuits, where the output is a pure function of the present input only. This is in contrast to sequential logic, in which the output depends not only on the present input but also on the...
between them will generate a unique CRC signature over a large enough sample of random inputs. So all an IC need do is store the expected CRC signature and test for it after a large enough sample set from the PRNG. The CRC comparison with expected signature or the actual resultant CRC signature is typically accessed via the JTAG IEEE
Institute of Electrical and Electronics Engineers
The Institute of Electrical and Electronics Engineers is a non-profit professional association headquartered in New York City that is dedicated to advancing technological innovation and excellence...
1149.1 standard.
There are several specialized versions of BIST which are differentiated according to what they do or how they are implemented:
- Programmable built-in self-testPBISTProgrammable Built-In Self-Test is a memory DFT feature that incorporates all the required test systems into the chip itself. The test systems implemented on-chip are as follows:* algorithmic address generator* algorithmic data generator...
(pBIST) - Memory built-in self-test (mBIST) - e.g. with the Marinescu algorithm
- Logic built-in self-test
- Analog and mixed-signal built-in self-test (AMBIST)
- Continuous built-in self-test (CBIST)
- Periodic built-in self-test
- Interrupt-driven built-in self-test (IBIST) or user-initiated built-in self-test
- Power-up built-in self-test (PupBIST)
- Automatic built-in self-test (ABIST)
See also
- Embedded systemEmbedded systemAn embedded system is a computer system designed for specific control functions within a larger system. often with real-time computing constraints. It is embedded as part of a complete device often including hardware and mechanical parts. By contrast, a general-purpose computer, such as a personal...
- System engineering
- Safety engineeringSafety engineeringSafety engineering is an applied science strongly related to systems engineering / industrial engineering and the subset System Safety Engineering...
- Watchdog timerWatchdog timerA watchdog timer is a computer hardware or software timer that triggers a system reset or other corrective action if the main program, due to some fault condition, such as a hang, neglects to regularly service the watchdog A watchdog timer (or computer operating properly (COP) timer) is a computer...
External links
- Hardware Diagnostic Self Tests
- BIST for Analog Weenies - A Brief general overview of the capabilities and benefits of BIST by Analog Devices.