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| A High-Performance Open Source Oscilloscope: development log & future ideas |
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| Marco:
--- Quote from: nctnico on December 07, 2020, 12:02:11 am ---if you want to capture a glitch with 100% percent certainty during a given interval the only way out is deep memory (+analysis) or triggering (combined with infinite persistence and/or saving a screendump). --- End quote --- It's much easier to compare a capture against bounds relative to a reference signal on the fly than doing digital persistence on the fly. Linear memory access vs. defacto random access. |
| tv84:
--- Quote from: Marco on December 07, 2020, 07:06:38 pm ---It's much easier to compare a capture against bounds relative to a reference signal on the fly than doing digital persistence on the fly. --- End quote --- Can you elaborate on what you mean by "digital persistence on the fly"? |
| tom66:
I feel persistence will be quite easy to implement. In infinite persistence, pixels are only updated if the value is greater than the previous - this can be adjusted at the final framebuffer stage so there are relatively few pixel values to compare. For variable persistence a moving average filter could be used although that would have a non-linear decay function (not sure if this is a problem.) Alternatively N buffers (~1024x256x16) would need to be stored and summed together although this would get computationally very expensive for longer persistence periods. It seems that Tek use an interesting approach for variable persistence on their newer scopes. They apply a random noise function to the previous buffer, which models the approximate desired persistence. The disadvantage of this method is that the trace constantly looks noisy. |
| Marco:
--- Quote from: tv84 on December 07, 2020, 07:24:22 pm ---Can you elaborate on what you mean by "digital persistence on the fly"? --- End quote --- Trying to updating the bucket counts for persistence at full sample rate is pretty much impossible, determining if it's within a given bound of a reference signal fairly trivial. |
| tom66:
--- Quote from: Marco on December 08, 2020, 12:07:42 am ---Trying to updating the bucket counts for persistence at full sample rate is pretty much impossible, determining if it's within a given bound of a reference signal fairly trivial. --- End quote --- What do you mean by this? Testing every sample against a reference signal is still fairly expensive. Mask testing after the waveform is captured is relatively easy and could be done in the rendering engine. The mask could be defined by some % of the signal e.g. 99% of all samples which could be gathered after say ~30 seconds of persistence data is collected. |
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