Boundary-scan is a well
established test technology. Boundary-scan has been in use since
the early 1990s when the Joint Test Action Group (JTAG) devised
a solution to testing the many new printed circuit boards that
were being developed and manufactured where there was little or
no physical access for test probes. Once boundary-scan was
established, the next step was to develop a standard modeling
language for silicon vendors to model their boundary-scan
devices, for tool vendors to develop automation tools, and for
end-users to create boundary-scan tests. Thus the Boundary-Scan
Description Language (BSDL) was created.
BSDL is the standard modeling
language for boundary-scan devices. Its syntax is a subset of
VHDL and it complies with IEEE 1149.1-2001. It is used by
boundary-scan test developers, device simulators, semiconductor
testers, board level testers, and anyone using boundary-scan.
The use of BSDL promotes consistency throughout the electronics
industry. Additionally, it enables the specification of any
boundary-scan functions on a device in a useful, understandable,
and consistent manner.
BSDL came out of the development
of the boundary-scan test philosophy. The initial IEEE
1149.1-1990 (see [IEEE 1149.1 (JTAG)]) standard describing
boundary-scan was approved and released in 1990, and as a result
the use of boundary-scan techniques started to grow. The next
revision of the standard occurred in 1993. In 1994 a further
revision incorporated BSDL into the IEEE 1149.1-1994 standard.
What is BSDL?
The Boundary-Scan Description
Language enables users to provide a description of the way
in which boundary-scan is implemented in any particular
device. As each chip designer tends to apply the
boundary-scan standard in a slightly different way, it is
necessary to express tests in a comprehensible, specific and
BSDL is written within a subset
of VHDL. VHDL is commonly used as a design-entry language
for FPGAs and ASICs in electronic design automation of
digital circuits, and as such it is suitable for work with
boundary-scan since design of many chips is performed using
this language. However BSDL is a "subset and standard
practice" of VHDL, i.e., the scope of VHDL is thereby
limited for boundary-scan application.
During the design of BSDL there
were two main criteria for the language:
BDSL enables accurate and
useful descriptions of the features of a device that uses
boundary-scan. The BSDL file is used by the boundary-scan
tools to make use of the device features to enable test
program generation, failure diagnosis, as well as use in any
testability analysis. BSDL is not a language that can be
used for hardware description; rather, it is used to define
the data transport characteristics of the device, i.e. how
it captures, shifts, and updates scanned data. This is then
used in defining the test capability. The BSDL file includes
the following data:
The Entity Declaration is a VHDL construct that is used
to identify the name of the device that is described by
the BSDL file.
The Generic Parameter is the section that specifies
which package is described.
Logical Port Description:
This description lists all the connections on the
device. It defines its basic attributes, i.e., whether
the connection is an input (in bit;), output (out bit;),
bi-directional (inout bit;) or if it is unavailable for
boundary-scan (linkage bit;).
Package Pin Mapping:
The Package Pin Mapping is used for determining the
internal connections within an integrated circuit. It
details how the pads on the device die are wired to the
Use Statements: This
statement is used to call the VHDL packages that contain
the data that are referenced in the BSDL File.
Scan Port Identification:
The Scan Port Identification identifies the particular
pins that are used for the boundary-scan / JTAG
implementation. These include: TDI, TDO, TMS, TCK and
TRST (if used).
Test Access Port (TAP)
Description: This entity provides additional
information on the boundary-scan or JTAG logic for the
device. The data includes the instruction register
length, instruction opcodes, device IDCODE, etc.
Description: This description provides the structure
of the boundary-scan cells on the device. Each pin on a
device may have up to three boundary-scan cells, each
cell consisting of a register and a latch.
How is BSDL used?
When a board is designed,
boundary-scan-compliant devices are organized into "chains".
Scan chains form the basis for board-level and system-level
tests that can detect and diagnose pin-level structural
faults such as opens and shorts. Automated tools are used to
generate test programs or procedures for the boards. The
most important inputs to this process are the BSDL files for
boundary-scan-enabled devices, and the netlist that
describes the interconnects between the devices of the
board. The generated test program, when applied to a target
board, reports the structural test failures and can be used
to help with board repair.
Some tools are able to use
boundary-scan to create test patterns for clusters of
components that include non-boundary-scan-compliant devices,
and other tools can generate test patterns that an on-board
processor can run to enable at-speed functional testing.
These test procedures are applied stand-alone or in
conjunction with other test techniques, such as In-Circuit
Testing (ICT), with an overall goal of producing optimal
test coverage at the lowest cost and the shortest test
The Boundary-Scan Description
Language, BSDL, is widely used within the IEEE 1149.1 / JTAG
community to enable consistent, accurate and useful
information to be defined for a boundary-scan-enabled
device. In this way, the chip can be incorporated into a
design, and its capabilities used to their full in the most
The Boundary-Scan Description
Language (BSDL) specification is contained in the IEEE 1149.1
standard which can be obtained from
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