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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

Hello James,

thank you very much for your detailed explanation. The 1 cycle "multi-cycle"-instruction (that takes 2 cycles in reality) is the way to go. I simple ignore the warning and change the (default) value of 2 cycle-duration to 1 cycle. However, I still think that the documentation is misleading in this point.

Your tip with the combinatorial instruction that just read is not allowed by my SOPC-builder (I am using Nios 2 1.01, Q II 4.1, I have not received my upgrade yet), it displays an error like "no external ports allowed for comb. instructions", even if I only declare external inputs. Maybe this is already improved in Nios2 1.1 ?

However, this "real" single-cycle solution would not fit in my case, because I also generate a "next data please" signal, which of course should not be generated speculatively. I suppose there is no way the detect if my custom combinatorial instruction was killed after specul. execution?

Regards

Thomas