Mid Cross — Control Systems/Pulse Metrics

Mid Cross

Control Systems / Pulse Metrics

Reports when a bilevel waveform last crossed its mid reference level, and in which direction – the streaming counterpart of MATLAB's midcross. One crossing is reported per transition, not per raw crossing of the level: a transition is a pair of consecutive settled samples in opposite states, and its instant is the FIRST mid crossing between them, linearly interpolated (IEEE Std 181-2003 Sec 5.3.3). Noise that flicks across the level while the waveform is still settled in a state produces no crossing at all.

Ports

• u – the bilevel waveform to measure. Scalar – see Notes.
• tc – the instant of the most recent transition, in seconds measured from the start of the run, held until the next one. Scalar.
• edge – +1 on the sample that reports a rising transition, −1 for a falling one, and 0 on every other sample. It is the one-sample marker that says the value on tc is new.

Parameters

• Low State Level – the value the waveform sits at in its low state. 0 by default.
• High State Level – the value it sits at in its high state. 1 by default. Every threshold below is a percentage of the distance between these two, so they must differ.
• State Level Tolerance (%) – how far into the amplitude a sample must be before it counts as having settled into a state. 2 by default, the value IEEE Std 181-2003 uses. Samples between the two boundaries belong to no state and are treated as part of a transition.
• Mid Percent Reference Level – the level whose crossing DATES a transition, as a percentage of the amplitude. 50 by default, which is the mid point IEEE Std 181-2003 uses and what MATLAB calls MidPercentReferenceLevel. It must lie strictly between the tolerance and 100 minus it.
• Sampling Time (s) – zero or less inherits the solver's rate; a positive value runs the block at that period.

Code export

All ten targets: Python, MATLAB, Java, Rust, C, C++, VHDL, Verilog, SystemVerilog and PLC Structured Text.

Every threshold is structural and is inlined into the comparisons at export time rather than exposed as a tunable parameter – they follow from the state levels and the percentages, and the emitted core carries the numbers rather than the percentages. Re-export after changing any of them.

⚠ The three HDL targets are simulation-only. They carry this block's arithmetic in real rather than Q16.16, quantising only at the port boundary, for a reason specific to what it measures: an instant is a sample index plus a fraction, and a 16-bit integer part runs out after 32767 samples – five and a half minutes at a 10 ms rate. The comparisons and the interpolation are exact in real, which is what makes the exported core agree with the simulation; a synthesizable variant would have to carry the index some other way and is not what this block offers.

Simulink bridge

No equivalent (Support::None). Measured rather than assumed: a find_system sweep over 22 DSP System Toolbox and Simulink libraries on R2026a finds no block matching duty, pulse, rise, fall, slew, overshoot, settling or state level – the whole Pulse Metrics group is MATLAB functions with no Simulink counterpart. The bridge reports this block rather than dropping it silently, and it therefore has no parity testbench. Code export verification still covers it across all ten languages.

Notes

• Stateful, and discrete by nature (setDiscreteOnlyBlock(true)): the tracker advances once per sample.
• A measurement appears one sample after the transition that produced it, in the live run and in all ten exported languages alike. A hardware block cannot read back a value it computes in the same clocked interval, so publishing immediately would put the three HDL targets one sample behind the other seven on every edge; the delay is uniform instead, and deliberate.
• Crossing instants are interpolated between the two samples that straddle a reference level, exactly as IEEE Std 181-2003 Sec 5.3.3.2 specifies and MATLAB implements – so a measurement is not quantised to the sampling period.
• The output is 0 until the first measurement exists, and holds its last value between them. A run that never settles into both states produces no transitions and the output stays at 0.
• The state levels are PARAMETERS here, not estimated from the data. MATLAB's pulse-metric functions call statelevels to guess the two levels from a histogram of the WHOLE signal when you do not supply them; that is a batch operation over samples a streaming block has not seen yet. This block takes the levels the way those same functions do when you pass 'StateLevels' explicitly.
• Scalar only. One waveform and its own tracker; wire one block per channel.
• No state space. The block is not linear in its input – it is a sequence of comparisons – so it carries none and model reduction correctly declines to merge it.
• The instant is measured from the start of the run, not from the model's absolute time origin. The block counts its own samples rather than reading a clock, which is what lets all ten exported cores produce the same number without one of them carrying a different notion of when zero was.
• MATLAB's second return value is the mid reference LEVEL, which here is a constant derived from the parameters; it is not worth a port and is not offered.