2.4.8. Filtering Relevant Samples
The Signal Tap logic analyzer offers a snapshot in time of the data that the acquisition buffers store. By default, the Signal Tap logic analyzer writes into acquisition memory with data samples on every clock cycle. With a non-segmented buffer, there is one data window that represents a comprehensive snapshot of the data stream. Conversely, segmented buffers use several smaller sampling windows spread out over more time, with each sampling window representing a contiguous data set.
With analysis using acquisition buffers you can capture most functional errors in a chosen signal set, provided adequate trigger conditions and a generous sample depth for the acquisition. However, each data window can have a considerable amount of unnecessary data; for example, long periods of idle signals between data bursts. The default behavior in the Signal Tap logic analyzer doesn't discard the redundant sample bits.
The Storage Qualifier feature allows you to establish a condition that acts as a write enable to the buffer during each clock cycle of data acquisition, thus allowing a more efficient use of acquisition memory over a longer period of analysis.
Because you can create a discontinuity between any two samples in the buffer, the Storage Qualifier feature is equivalent to creating a custom segmented buffer in which the number and size of segment boundaries are adjustable.
There are six storage qualifier types available under the Storage Qualifier feature:
- Continuous (default) Turns the Storage Qualifier off.
- Input port
Upon the start of an acquisition, the Signal Tap logic analyzer examines each clock cycle and writes the data into the buffer based upon the storage qualifier type and condition. Acquisition stops when a defined set of trigger conditions occur.
The Signal Tap logic analyzer evaluates trigger conditions independently of storage qualifier conditions.
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