Error detection/correction and fault detection/recovery – Pulse or data error handling – Digital logic testing
Reexamination Certificate
1998-06-02
2001-10-30
Tu, Christine T. (Department: 2784)
Error detection/correction and fault detection/recovery
Pulse or data error handling
Digital logic testing
C714S724000, C370S244000
Reexamination Certificate
active
06311303
ABSTRACT:
BACKGROUND
1. Field of the Invention
This invention relates to methods and interfaces for facilitating testing or debugging an integrated circuit.
2. Description of Related Art
Debugging a problem in an integrated circuit (IC) is generally easier using a simulation of the IC rather than an actual IC because a simulation allows a circuit designer to probe the state of every signal and register in every module of the IC. The same design, when in the form of an IC, is more difficult to debug because most signals that the designer wants to observe are internal signals that are not connected to any I/O cells. However, significant debugging of actual integrated circuits is often required before an IC design is fully operational under a variety of system conditions.
One way to observe an internal signal for debugging is with a probe that can contact a pad or other structure within an IC, to measure a signal at the contact point. However, the small size of such structures make probing extremely difficult. Additionally, such structures are generally inaccessible when the IC is fully packaged. Focused ion beam (FIB) technology provides one method of bringing an internal signals out of an IC. FIB techniques “jump” an internal signal that a designer wants to observe, to an output line. A cost of jumping an internal signal to an output line is the loss of the function of the output signal normally on the line. The designer may be able to jump an internal signal to a non-critical output signal, but finding enough non-critical output signals becomes more difficult as the number of internal signals to be observed increases. Further, using FIB technology becomes tedious and expensive if the internal signal and the output signal are widely separated in the IC.
Accordingly, methods and circuits that permit observation of internal signals for debugging of an IC are desired. Further, such methods and circuits are sought which can be used on packaged IC and do not required jumping of signals, alteration of the IC, or precise positioning of probes.
SUMMARY
In accordance with the invention, an integrated circuit, such as a host adapter IC, includes a monitor port, several circuit modules, and a selection circuit that selects which of the circuit modules drives an internal signal through the monitor port. The internal signal, while not required as output signals for the normal functions of the integrated circuit, are useful for debugging. A debugging process can observe the internal signals at the monitor port to identify problems in the integrated circuit. If a particular module is identified as having a problem, that module can be selected for driving the monitor port. Alternatively, the modules can be selected and observed one by one to identify which module may have a problem and the specific origin of the problem.
In one embodiment, the selection circuit includes a trace bus and enable lines. The trace bus runs serially from the monitor port to each circuit module, and each module has tri-state buffers that connect the module to the trace bus. The select circuit uses the enable lines, which are coupled to enable terminals of the tri-state buffers, to select which circuit module drives each line. Preferably, only one module drives all the trace bus lines simultaneously so that only one enable line is required per module. Alternatively, multiple modules can drive different lines (or bits) of the trace bus. An alternative selection circuit includes a multiplexer with input ports coupled to the circuit modules via parallel buses. In either embodiment, a trace select register controls which circuit module drives the monitor port, and control registers or the current operating mode of each module select which set of internal signals the circuit module applies to the monitor port. Accordingly, a large number of internal signals can be easily selected and observed through the monitor port when debugging the integrated circuit.
REFERENCES:
patent: 4439858 (1984-03-01), Petersen
patent: 5132614 (1992-07-01), Sakumoto et al.
patent: 5189675 (1993-02-01), Nozuyama et al.
patent: 5909450 (1999-06-01), Wright
Devanagundy Uday N.
Gates Stillman F.
Adaptec, Inc.
Millers David
Skjerven Morrill & MacPherson LLP
Tu Christine T.
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