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Altera_Forum's avatar
Altera_Forum
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21 years ago

Fast data access with Nios II ?

I have tried to quickly access external data with a custom instruction. After I have realized, that 1 cycle-custom-instructions cannot have external connections, I implemented a 2-cycle custom instru...
Altera_Forum's avatar
Altera_Forum
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21 years ago

for two cycles remember that:

Cycle 1 --> your hardware has to latch the data

Cycle 2 --> your hardware has to process the data

Cycle 3 --> the Nios has to read it back

So when you think of two cycle you imagine steps 1 and 2, however you are creating the custom instruction for the Nios which has it's own latching to do. I was thrown off by this the first time I did a CC but after that I just got into a habit of figuring out the cycles for my hardware and adding one.

In the Nios II ref. manual the latencies of the instructions are listed there. Being able to access memory across a bus in 2 cycles would result in a low fmax I'm sure.