Interface Analysis
Interface analysis is a technique
to verify that the inputs and outputs of the complex electronic device
are consistent with the defined signals, outputs, inputs, and data of
the rest of the system. In addition, the technique looks for inputs and
outputs that do not connect with other elements of the system (missing
items).
Interface analysis is a
manual analysis, with an assurance engineer comparing the description
of the complex electronics with other system documentation. If the
various system and sub-system requirements and designs are included in
a data repository, it may be possible to use a tool to automate the
analysis. The use of a checklist or worksheet may help the assurance
engineer confirm the status of all inputs and outputs.
This page describes Requirements Interface Analysis for external
interfaces and Design Interface Analysis for
internal interfaces.
Requirements Interface Analysis
Interface analysis
verifies that the requirements for the complex electronics interfaces
with other hardware, software, users, and other systems are correct,
consistent, complete, accurate, and testable. At the requirements
phase, the main goal is to ensure that the system-level data and
communication paths are consistent and complete. At the board level,
the analysis should show that the complex electronics device inputs and
outputs match those specified for the circuit board.
Inputs to the Requirements Interface Analysis
- Complex Electronics
specification/requirements
- Circuit board and/or sub-system
specifications
- System specification
- Interface documentation (formal or
informal)
- System and sub-system descriptions
- Operational concepts
- Product information (e.g. for the
complex electronic device)
Process
Interface analysis is a
manual analysis that compares the inputs and outputs of the complex
electronic device with the corresponding connections from the system.
Each input to the complex electronics is traced to the part of the
system that provides that input, and the characteristics of the input
(e.g., voltage level, type of signal, acceptable range) are checked
against the description of what the system will provide. The same is
done for the outputs of the complex electronics. In addition, the
process of comparing the inputs and outputs should identify any signals
that are orphans (do not come from or go to another part of the system)
or undefined.
When performing an
interface analysis for a complex electronic device, you want to focus
on these areas:
- Physical. Check the number of pins on the device,
and ensure that it matches the number on the circuit board
drawing. If pin assignments are defined, verify that they are
consistent between the circuit board and the complex electronics
specification. Also check for pins that are undefined or floating.
- Power. Are the correct voltages applied to
power pins? Is the correct type of power (A/C, D/C) provided? Are
the ground pins connected? What voltage levels (range) are
acceptable for the input or output? What voltage is considered a
“high” or a “low” for logic values? Are
fan-in and fan-out requirements met?
- Signals. Verify that input signals match the
output signals of other devices. Verify that every input signal
comes from somewhere, and that every output signal is used by some
other device. Verify that the types of signals are correct and
consistent. Check timing requirements for the signals.
- Communications. If the complex electronics will
implement any communication schema, verify that the specification
is correct for that schema, and consistent with other elements of
the system. Check any defined messages or data for consistency
across the interface.
- System-level. Take a step back from the details and
consider how the complex electronics works within the system. Look
at the functions the device has to implement and consider whether
the correct inputs are provided to the device. Will the device
have enough information to perform its expected functions? Also
look at the broader data and communications paths. Are there any
bottlenecks that could affect the timing of data coming into the
complex electronics, or slow down any outputs on the way to other
devices? How would failure of one part of the communication path
affect the complex electronic device?
Outputs of the Requirements Interface Analysis
- Analysis Report
- Identified issues, inconsistencies, or
errors
The primary output of an
interface analysis is a report detailing the process followed, the
documents used, and the final results. The formality of the report will
vary with the complexity of the project, and with any contractual
requirements. For small projects, the information can be provided in an
e-mail or one-page report. For large and complex projects, a multi-page
report will often be necessary, with review and signature by the
analyst, the project manager, and perhaps others.
If the interface
analysis identifies problems or inconsistencies, these should be
provided to the project using their problem reporting method. The
assurance engineer should follow-up on the issues, to assure that the
problems are resolved and the documentation is updated.
Design Interface Analysis
While the requirements
interface analysis verified the external
interfaces for the complex electronics, the design interface analysis
looks at the internal interfaces. Signals
come in to the device, are processed, and an output is generated. The
internal connections along the way need to be consistent (e.g., digital
ground to digital ground) and correct.
At the design stage, the
external interfaces should be re-verified. The Design Interface
Analysis should be performed first on the behavioral model (to verify
that the signals are handled consistently) and then on the detailed
design.
Inputs to the Design Interface Analysis
- Complex Electronics design, including
HDL models and written documents
- The worksheets (or other documents) from
the Requirements Interface Analysis
The following documents
may be useful as references:
- Complex Electronics
specification/requirements
- Circuit board and/or sub-system specifications
- System specification
- Interface documentation (formal or
informal)
Process
At the design stage,
interface analysis traces the input signals through the design and
verifies that the signal type, range, voltage, and other factors are consistent.
Output signals are traced back into the design to verify the same
characteristics. This is a manual analysis that compares the inputs and
outputs of the signal at each connection within the design.
When performing an
interface analysis for a complex electronic device, you want to focus
on these areas:
- Logical. Logical blocks take inputs, process
them, and provide outputs. Check the description of the logical
block and verify that the correct types of inputs are provided.
Make sure that no inputs are undefined or floating.
- Power. At each internal connection, verify
that the voltage levels (range) are consistent. For example, if
the signal is +/- 5V, it should not suddenly become+/-10V
somewhere in the design. Check for consistency in the
“high” and “low” voltages for logic
values.
- Signals. At each internal connection, verify
that input signals match the output signals of other
devices/blocks. Verify that every input signal comes from
somewhere, and that every output signal is used by some other element.
Verify that the types of signals are correct and consistent. Check
timing requirements for the signals.
Outputs of the Design Interface Analysis
- Analysis Report
- Identified issues, inconsistencies, or
errors
As with the requirements
interface analysis, the report should indicate the inputs used, methods
followed, and final results. Problems and issues should be worked
through the appropriate project channels.
|
