Hardware Comparison
Hardware comparison allows the NI 655x to verify that a DUT returns the correct response data under different use cases and stimulus data.
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Note Real-time hardware comparison is supported with only the NI 655x devices. Other NI digital waveform generator/analyzers, such as the NI 654x/656x support acquiring the data into PC memory for analysis. |
There are two primary methods for comparing acquired response data with expected data. With the first method, the NI 655x captures the actual response data into PC memory and uses software to post-process the results. The software uses only the two basic logic states, 0 and 1, to configure the testers stimulus data. With the second method, you can preload the NI 655x with both stimulus and expected response data and make real-time comparisons as data is acquired. Whenever a waveform contains a comparison logic state (H or L), then the acquired response data is compared to the expected response. You can choose whether this real-time hardware comparison operation drives and compares data (Stimulus and Expected Response mode) or whether it only acquires and compares (Expected Response Only mode).
Data comparison logic in the onboard FPGA connects the generation and acquisition circuitry. The data decoder receives data from onboard memory and enables/disables the driver based on the logic state of each sample. The decoder transfers the expected response to the acquisition engine. A FIFO allows the alignment of the actual response with the expected response. If an error is detected during the comparison, then information on the fault is stored separately from the acquired data so the application software can retrieve both types of information for further analysis.
The device stores the following information for each fault detected:
- Sample number of the fault
- Channel(s) at fault
- Total number of repeated errors (useful if the Filter Repeated Sample Errors property or the NIHSDIO_ATTR_HWC_FILTER_REPEATED_SAMPLE_ERRORS attribute is enabled)
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