Interview Question 7: Enhance the memory

You are given a one port memory block as shown below.

In past you used this memory to design an application where you performed one read or write operation every clock. Now in next generation product you are asked to double the performance. How will you accomplish it? Brainstorm multiple scenarios.
For example:

1. How will you modify the design if you could double the clock at which memory can run?

2. What if you can not double the clock speed? How will you modify the design if you are asked to use memory at the same clock period as the surrounding logic.

I know, it is difficult to take out juice from the memory like this. What if you are asked just to allow (WRx + RDy) or (RD0 + RD1) combinations only? You may also use more than one memory to solve this problem.

Interview Question 6: 7 bit 1’s counter using 1 bit adders.

You are given a basic 1 bit adder block as shown below. 

How can you use this building block to create a module which finds out number of 1s in a 7 bit input?

Interview Question 5: Design / Architect a solution

Design a solution (state machine, timing diagrams etc) for following problem.

Followup question: What are the possible error conditions. How to  find and recover from them?

Interview Question 4: Digital Delay

You are asked to design a 512 Clock Digital delay. A 32 bit data is fed to this module. It comes out after 512 clocks at the output.
- What is the most efficient way to design this block?
- What happens if data widths of input and output change? For example {32,64} or {64,32}?

- Where such huge delays are used?

Interview Question 3: Random number generator with weights

Generate random numbers such that they follow certain needed pattern. For example out of 100 generated random numbers.

35% should be    5
20% should be   25
10% should be   123
35% should be   73

The naming is confusing. The set of output numbers is small. You are just creating numbers from a small set {5,25,123,73} but the sequence of output numbers is random or unpredictable.

Can you think of any application or test bench mechanism where such numbers are needed?

Interview Question 2: Find the largest bit in 64 bit number

Problem: You are asked to design a hardware which takes in a 64 bit number and finds out the largest position of  “1”.  For example if the input number is “00001010101111000” then the output should assert “1100” or 12 in decimal.

You can also dive deeper and find out corner cases and suggest how to fix them.
Also try to create solution which will be synthesis friendly and produces smallest and fastest solution.

Interview Question 1: Design a Tape Reader

Problem 1: Design a tape reading system. The tape contains 2^n - 1 numbers. One number is missing on the tape. Design hardware + software system to read the numbers and find out the missing number.
Assumptions:
- Tape is continuous. Assume that you have enough low level components given to identify and read a number.

Problem 2: The similar problem is posed with 2*n + 1 numbers. 2*n numbers are in pairs. For example
{10,10, 21,21,3} and you need to find out the odd number which is 3 in this example.
The numbers are not in any particular order. For example in the above example the numbers might occur as
{10,3,21,10,21}. The “n” is large.

You will notice that this is an open ended question. The interviewer is not looking for a fixed answer. Rather he is looking for a matured approach which shows how a person thinks and applies his existing knowledge in solving a given problem.

Block diagram of the desired system