LM101 is an Integrator fed by a current derived from the magnitude of the input control voltage. The output of the intergrator is the triangular wave output. The triangle amplitude trips a LM111 voltage comparator with a large hysteresis, so sets the peak amplitude (both positive peak and negative peak). The square wave output is used to switch the integrator such that it integrates either in the positive direction or the negative direction, depending the square wave.