DSP math interview questions and fundermentals

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GhostInABox

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Hi All,

I have a 2 questions
1. What are the most critical maths you need to know when going for a DSP + FPGA interview ? , e.g multiplying 2 N bit numbers will take up 2* N bits.

2. How many bits are needed for a MAC unit ( say you have two 16 bits inputs to a multiplier which goes in the a accumulator of 40 bits) . I dont understand how the extra 8 bits ( 40 bits - 32 bits ) allow us to do add up to 256 32 bit numbers.

A good example is provided here **broken link removed** ,but i dont really understand how the generalized formula is contructed for a N bit MAC , adding M times.

Any help is appreciated
 

Hi,

I dont understand how the extra 8 bits ( 40 bits - 32 bits ) allow us to do add up to 256 32 bit numbers.
Do a worst case test:
The max int32 value is 0xFFFFFFFF
Adding this up 256 times is the same as multipling the value by 256.
256 (decimal) = 0x100
0xFFFFFFFF x 0x100 = 0xFFFFFFFF00

Each hex nibble is 4 bits. --> 10 hex nibbles are 40 bits.

Klaus
 

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