q[t] is a switching function, and I want to mark the corresponding time point when the value of q[t] changes from 1 to 0 in the curve. How should I rewrite my code? (From the code, it can be seen that when Mod [t, \ [Tau]]=(2/3) \ [Tau], q[t] changes from 1 to 0.)

The code:

tstart = 0;
tend = 0.06;
step = 0.00000005;
n = (tend - tstart)/step;
system = {vi q[t] == l iL'[t] + vC[t], 
   vC'[t] == iL[t]/c - vC[t]/(r c), vC[0] == 0, iL[0] == 0};
control = {q[0] == 1, 
   WhenEvent[Mod[t, \[Tau]] == (2/3) \[Tau], q[t] -> 0], 
   WhenEvent[Mod[t, \[Tau]] == 0, q[t] -> 1]};
pars = {vi -> 24, r -> 22, l -> 2 10^-2, 
   c -> 1 10^-4, \[Tau] -> 2.5 10^-5};
sol = NDSolve[{system, control} /. pars, {vC, iL, q}, {t, 0, .2}, 
   StartingStepSize -> step, 
   Method -> {"FixedStep", Method -> "LinearlyImplicitEuler"}, 
   DiscreteVariables -> q];
a = Evaluate[iL[t] /. sol];
b = Evaluate[vC[t] /. sol];
p1 = Plot[{a}, {t, 0, 0.08}, AxesLabel -> {"s", "il[t]/A"}, 
  PlotLegends -> {"LinearlyImplicitEuler"}, PlotStyle -> {Green}, 
  PlotRange -> All]
p2 = Plot[{b}, {t, 0, 0.08}, AxesLabel -> {"s", "vc[t]/A"}, 
  PlotLegends -> {"LinearlyImplicitEuler"}, PlotStyle -> {Yellow}, 
  PlotRange -> All]