Looks like 'swept' signal.

The square wave frequency is being increased (swept) from x(Hz) to y(Hz) by a modulating waveform. It 'looks' like it's sweeping from around 2kHz to 3kHz by a low (250Hz???) signal.

Configure an output to a 2kHz square wave and arrange for it to increase by 4Hz every 4uS until it reaches 3kHz then repeat.