  We show how the quantum Hall effect in an inverted-gap semiconductor (with
electron- and hole-like states at the conduction- and valence-band edges
interchanged) can be used to inject, precess, and detect the electron spin
along a one-dimensional pathway. The restriction of the electron motion to a
single spatial dimension ensures that all electrons experience the same amount
of precession in a parallel magnetic field, so that the full electrical current
can be switched on and off. As an example, we calculate the magnetoconductance
of a p-n interface in a HgTe quantum well and show how it can be used to
measure the spin precession due to bulk inversion asymmetry.
