x axis non-uniform labeling

I’m trying to find a glitch in an FPGA simulation. The data stored in a file is:
(simulation time, y)

In reality, if I plot that I get large gaps because the simulation time continues and data is only output periodically. In other words simulation time is not continuous. I’d like to view the data without the gaps, but with simulation time annotating the x-axis so I can determine where the glitch occurs.
I’ve tried a variety of things:
#ax1.plot(x1, x1,‘b–’)
#ax3 = ax2.twiny()
ax2.set_xticklabels(simtimedata, fontdict=None, minor=False, rotation = 45)
ax2.plot( idatanp.real,‘k–’,idatanp.imag,‘g.-’)
#ax2.plot(xdat, idatanp.real,‘k–’,xdat,idatanp.imag,‘g.-’)
#ax3.plot(simtimedata, idatanp.real,‘k–’,alpha=0)

but cannot get the axis to both show the data all together AND show where the glitch occurs. I thought the twiny might help to put another x axis up so I could plot the data first with the x axis incrementing based on when the data is read in, and then trying to place labels showing simulation time.

Does anyone have any ideas how I could do this?