# Interview Question -- Design a module that receives a Stream of 20MB/s...

Thread Starter

#### swaviram

Joined Jan 25, 2022
7
Hey All,

I would like to get your help with the following question that I got in an interview and have not succeeded to solve it yet.

Design a module that receives a Stream of 20MB/s, with an input width of 8 bits (Byte).
The output stream should be 5 bits wide
.

+ Explain the problem, as you see it.
+ Share a diagram block.
+ Code (Schematic or Behavioural) that applicates the solution.
+ What is the rate of the output ?
+ What are the constraints or problems in this solution?

#### drjohsmith

Joined Dec 13, 2021
852
what have you so far ?
Have you had the interview ?

Thread Starter

#### swaviram

Joined Jan 25, 2022
7
I have not had the interview yet.
I have it next week, but I really don't know how to start even.
I did not understand the probelm at all. I asked the interviewer for a clarification and he told me that the unit should convert between the formats (8 bit to 5 bit).
I feel like more info is missing. If someone could help me understand the problem so I could solve it, that would be great.

#### Ian0

Joined Aug 7, 2020
9,802
Don’t worry about vague questions. It means that you can answer your own interpretation of it, provided that you do answer the question as written and don’t contrive it too much as in this great Rowan Atkinson sketch.
So you could, for instance, split the input into 4-bit samples and output them at twice the speed, using the extra bit to indicate whether you are sending the top half or the bottom half

#### ericgibbs

Joined Jan 29, 2010
18,840
Design a module that receives a Stream of 20MB/s, with an input width of 8 bits (Byte).
The output stream should be 5 bits wide.
hi swaviram

You could consider the question literally, it actually sounds like a 'trip up' question.

input width of 8 bits (Byte).
Infers a 8 Bit parallel input

output stream should be 5 bits wide.
Infers a 5 Bit parallel output

constraints or problems in this solution?
Loss of resolution by re-transmitting only the 5 High Bits

receives a Stream of 20MB/s,
What is the rate of the output ?

transmits a Stream of 20MB/s,

E

#### BobTPH

Joined Jun 5, 2013
8,938
I guess it is a trick question since I see it very differently than @ericgibbs . I assume he means ALL of the data is to be transmitted as a stream of 5 bits- wide. There is an obvious problem with doing that though, which leads to constraints.

Bob

#### ericgibbs

Joined Jan 29, 2010
18,840
hi Bob,
I mean, the 3 low order Bits are not retransmitted,
Basically 8 wide wire in and 5 wires out, retransmitting only the 5 high order Bits.

E

Thread Starter

#### swaviram

Joined Jan 25, 2022
7
Don’t worry about vague questions. It means that you can answer your own interpretation of it, provided that you do answer the question as written and don’t contrive it too much as in this great Rowan Atkinson sketch.
So you could, for instance, split the input into 4-bit samples and output them at twice the speed, using the extra bit to indicate whether you are sending the top half or the bottom half
I'm really Junior, still a student...
How do I trasmit them at twice the speed? I understand the idea but how could I design it practically.
I'm lost here...

#### Ian0

Joined Aug 7, 2020
9,802
The trick is not to take my interpretation, but to interpret the question in a way you can answer it. @ericgibbs has a good suggestion on how to do that.
Is there an implication that no information should be lost? Or not?
Maybe you should be implementing some data-compression algorithm that keeps the same data rate?

It is unusual for parallel data to be transmitted with a fixed bit rate. It usually has additional lines to indicate when the data may be changing and when it is valid.

#### drjohsmith

Joined Dec 13, 2021
852
I would say
that the interviewer is wanting to see your design process,
can you identify the bits that can be ambiguous,
can you some up with suggestions

Its the sort of ill defined problem that one gets in engineering,
and an engineer will be able to "work the problem",

The fact your asking,
on a public forum ,
would suggest to me , that this might not be the job for you at this time

#### BobTPH

Joined Jun 5, 2013
8,938
Usually, an interview question like that is used to observe your thought pricess in tackling the problem, not even expecting an actual solution. But giving you the question ahead of time defeats that purpose. So, maybe it is intended to scare off unqualified candidates.

Bob

#### MrChips

Joined Oct 2, 2009
30,794
As others have pointed out, the purpose of being asked such a question in an interview is not to see if you have the correct answer.
There is no right answer. The purpose is to examine your problem solving and communication skills.

Thread Starter

#### swaviram

Joined Jan 25, 2022
7
I would say
that the interviewer is wanting to see your design process,
can you identify the bits that can be ambiguous,
can you some up with suggestions

Its the sort of ill defined problem that one gets in engineering,
and an engineer will be able to "work the problem",

The fact your asking,
on a public forum ,
would suggest to me , that this might not be the job for you at this time
That might be true...
Even though, this position is for junior with 0 experience.
I have not solved problem like this one...

#### Ian0

Joined Aug 7, 2020
9,802
Even though, this position is for junior with 0 experience.
they are probably hoping for someone with senior skills to whom they can pay junior wages.

#### drjohsmith

Joined Dec 13, 2021
852
they are probably hoping for someone with senior skills to whom they can pay junior wages.
It's probably the same question sheet for all engineering roles .
I'd certainly expect a university student to be able to work through the problem

Thread Starter

#### swaviram

Joined Jan 25, 2022
7
It's probably the same question sheet for all engineering roles .
I'd certainly expect a university student to be able to work through the problem
The problem is not well defined at all, and that's what made me very confused.
After asking for more clarification from him today, he said that I'm right and info is missing.
He said that the data indeed should be preserved after processing.

#### MrChips

Joined Oct 2, 2009
30,794
The problem is not well defined at all, and that's what made me very confused.
After asking for more clarification from him today, he said that I'm right and info is missing.
He said that the data indeed should be preserved after processing.
Pay attention. There is no acceptable solution to this question.
Hence, you make up your own scenario.
Try to think outside the box. Be a self starter and an independent thinker.

Thread Starter

#### swaviram

Joined Jan 25, 2022
7
Pay attention. There is no acceptable solution to this question.
Hence, you make up your own scenario.
Try to think outside the box. Be a self starter and an independent thinker.
Thank you very much!

#### AnalogKid

Joined Aug 1, 2013
11,036
What is the rate of the output ?
That is one of the questions.

I vote for the nybble-plus-flag solution.

ak

#### BobTPH

Joined Jun 5, 2013
8,938
It just occurred to me, if you wanted to ask a really devious interview question, giving it to him ahead of time, you could find one of the worst Instructable's out there, then word the question so that it comes up first in a google search. If they come to you with that "solution", they are disqualified.

Not saying that is the case here, just thought it was a good evil plan.

Bob

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