  We theoretically propose a method to perform in situ measurements of charge
noise during logical operations in silicon quantum dot spin qubits. Our method
does not require ancillary spectator qubits but makes use of the valley degree
of freedom in silicon. Sharp interface steps or alloy disorder in the well
provide a valley transition dipole element that couples to the field of an
on-chip microwave resonator, allowing rapid reflectometry of valley splitting
fluctuations caused by charge noise. We derive analytic expressions for the
signal-to-noise ratio that can be expected and use tight binding simulations to
extract the key parameters (valley splitting and valley dipole elements) under
realistic disorder. We find that unity signal-to-noise ratio can often be
obtained with measurement times below 1ms, faster than typical decoherence
times, opening the potential for closed-loop control, real-time recalibration,
and feedforward circuits
