Moving Average Filter (4 samples)

Four-sample moving-average filter with no reset input.

Behaviour:

• o_data is combinational and continuously equals (i_data + r_x1 + r_x2 + r_x3) / 4, with the fractional part discarded.
• r_x1, r_x2, and r_x3 hold the three previously stored samples. They are initialized to zero.
• On each rising edge of i_clk, i_data enters the delay line and the oldest sample is discarded.
• To observe the average associated with a new i_data value, apply it after an edge and read o_data before the following edge.

*Division by 4 is a right shift by 2 bits.*