Interview Question

Your manager has given you the task of implementing the following pseudo code in an FPGA:

if is_odd(a + d) {

p = (a + d)*2 + ((b + c) - 1)/4;

} else {

p = (b + c)*2 + d;

}

NOTES:

• You must use registers on all input and output ports.
• p, a, b, c, and d are to be implemented as 8-bit signed signals.
• A 2-input 8-bit ALU that supports both addition and subtraction takes 1clock cycle.
• A 2-input 8-bit multiplier or divider takes 4 clock cycles.
• A small amount of additional circuitry (e.g. a NOT gate, an AND gate, or a MUX) can be squeezed into the same clock cycle(s) as an ALU operation, multiply, or divide.
• You can require that the environment provides the inputs in any order and that it holds the input signals at the same value for multiple clock cycles.

Questions:

1. What is the minimum number of clock cycles needed to implement the pseudocode with a circuit that has two input ports?
2. What is the minimum number of ALUs, multipliers, and dividers needed to achieve the minimum number of clock cycles that you just calculated?
3. What is the minimum number of datapath storage registers (8, 6, 4, and 1 bit) and clock cycles needed to implement the pseudocode if the circuit can have at most one ALU, one multiplier, and one divider?

Good luck!!

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