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Altera_Forum
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14 years ago

Question about Custom User HDL

Hi, I try to implement a VHDL code as custom user HDL. The component that i need to release is an algorithme that determine the five greatest value for 16 input in one clock cycle. I compile th...
Altera_Forum's avatar
Altera_Forum
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14 years ago

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i confuse between custom instruction and SOPC Component. At first i belive they were the same, if you can that you give me the difference between it. When can i use custon instruction and when i use SOPC component.

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A custom instruction is something that can be inserted into the NIOS II processor pipeline.

An SOPC Component is a memory-mapped component that a NIOS II processor can access.

When you need to use one or the other is application dependent. An example of a custom instruction would be a multiply operation, and an example of a custom component would be a checksum accelerator.

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I will try to explain what i suppose to implement. I have PRC algorithm that contain 16 bloc of SBC( mentionned on the attached file).

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The attached file is meaningless without a timing diagram that shows the waveforms used to control this block. This is a good start, but it does not help explaining what you are trying to do.

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1- the result of this algorithm it valid on two clock cycle.

2- For me i search if i can implement it "Using a NIOS II processor using a custom instruction", if it is possible ok, else i implement it '"Using a NIOS II processor and software, with data in FPGA RAM".

I use this solution because i implement it using c, but it give a big execution time, about 18 microseond. Om my project i have a real time contraint, and my project should be execute on 0.5 microsecond.

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So what is the timing requirement; finish in two clocks, or finish in 0.5us?

If its finish in 0.5us, then at 100MHz, this is 50 clocks.

If the data that you are finding the highest five values in is continuously streaming into your FPGA, then the highest five values can be read at any time, and they will represent the five highest values that have come in so far.

The search algorithm is not the only important part of the design; where the data comes from is just as important.

Try to draw a block diagram of the system design first, and then look at the implementation of each of the components.

Cheers,

Dave