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# What is the real need of RTL

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#### phutanesv

##### Full Member level 2
Dear dudes,

As i know that RTL is Register transfer logic , which helps in transfering

to logics by using HDL's. or modelling of a digital system.

Suppose case1) we need to add two numbers we write c<=a+b

we give inputs to A and B. i check for functionality by simulating. if i get the

need i synthesis it. i get a hardware. in this case i know i am adding two numbers

fine.

Case 2) suppose i want to do z= k.a+(1-k) b

if k=0 i get 'b' and if k=1 i get 'a'

how to write a HDL for this , is RTL necessary

phutane

I may be missing something here, but I believe you're describing a mux...

assign z = k ? a : b

Hi,
In both cases your describing a combinational block one is adder, other mux. These blocks are used in describing some other functions which may be big, like these there are many combinational blocks like nand,nor, subtractor, comparator etc,. In large designs we do many operations on the data like additiion, comaprision, muxing etc. each operation takes some delay and all the data may not come simulataniously. In this case we need registers between different logics, this describes RTL. It also helps in increasing clock frequency.

I Hope it helps you

Regards
satyakumar

you should know the arrange of K , if k is a integer between 0,1,the equation will be tranlated into a mux , if k is a real , it will be a floating point adder.

Hi phutanesv,

ur case 2 simplifies to simple Mux if we are taking K as binary scalar

you cannot calculate or verify everything in a big design like this.. simulation by RTL is neccessary in designs to check its functionality for every possible inputs....

dear Designers,

my 2 cents in this discussion...

Let us define the Aim:
1. We need to realize in hardware.
2. How fast we can realize it and how can we automate it specific to the design related constraints.
3. Methodology to be more generic so the hardware can be realized in different process technologies (say 130nm/90nm...).
4. Ease in terms of Verification.

I believe these were the prime ingredients to drive a Register Transfer Language, where in we code in a bit higher level , what do we expect with in Registers (derived from micro architecture of a Requirement).

If you want to come with the hardware directly then no need for RTL, this is something more towards "CUSTOM Designing".

Praise the Lord.

best regards,
vlsichipdesigner
https://www.vlsichipdesign.com