5.8.1. Capturing Data Using Segmented Buffers
Each acquisition segment acts as a non-segmented buffer, continuously capturing data after activation. When you run analyses with segmented buffers, the Signal Tap Logic Analyzer captures back-to-back data for each acquisition segment within the data buffer. You define the trigger flow, or the type and order in which the trigger conditions evaluate for each buffer, either in the Sequential trigger flow control or in the Custom State-based trigger flow control.
The following figure shows a segmented acquisition buffer with four segments represented as four separate non-segmented buffers.
When the Signal Tap Logic Analyzer finishes an acquisition with a segment and advances to the next segment to start a new acquisition. The data capture that appears in the waveform viewer depends on when a trigger condition occurs. The figure illustrates the data capture method. The Trigger markers—Trigger 1, Trigger 2, Trigger 3 and Trigger 4—refer to the evaluation of the segment_trigger and trigger commands in the Custom State-based trigger flow. In sequential flows, the Trigger markers refer to trigger conditions that you specify within the Setup tab.
If the Segment 1 Buffer is the active segment and Trigger 1 occurs, the Signal Tap Logic Analyzer starts evaluating Trigger 2 immediately. Data Acquisition for Segment 2 buffer starts when either Segment Buffer 1 finishes its post-fill count, or when Trigger 2 evaluates as TRUE, whichever condition occurs first. Thus, trigger conditions associated with the next buffer in the data capture sequence can preempt the post-fill count of the current active buffer. This allows the Signal Tap Logic Analyzer to accurately capture all the trigger conditions that occurred. Unused samples appear as a blank space in the waveform viewer.
Each segment before the last captures only one sample, because the next trigger condition immediately preempts capture of the current buffer. The trigger position for all segments is specified as pre-trigger (10% of the data is before the trigger condition and 90% of the data is after the trigger position). Because the last segment starts immediately with the trigger condition, the segment contains only post-trigger data. The three empty samples in the last segment are left over from the pre-trigger samples that the Signal Tap Logic Analyzer allocated to the buffer.
For the sequential trigger flow, the Trigger Position option applies to every segment in the buffer. A custom state-based trigger flow provides maximum flexibility defining the trigger position. By adjusting the trigger position specific to the debugging requirements, you can help maximize the use of the allocated buffer space.
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