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Jan Waclawek
12/13/11 15:27
Read: 789 times

#185082 - silabs with cache
Responding to: Frieder Ferlemann's previous message
Thanks for the comment, Frieder.

I went to the Silabs datasheets and I think I know how it works, but I need to have this confirmed.
So, normally, in the 25MHz parts, the unconditional jumps take some cycles, say 3 for SJMP or 4 for LJMP; and the conditionals appear to take a different number of cycles depending on whether the jump is or is not taken, say 2/3 for JC and 3/4 for JB.

Now this means, that if there is a cache miss, the instruction may take 4 cycles more to fetch the word containing the target of the jump. That happens only when the jump is taken with the conditionals, so I should write say 3/4+4 for JB, correct?

My problem is, that the datasheet mentions also less-than-four-cycle cache-miss penalties. How comes? I couldn't really find the explanation in the datasheet, and did not dig deeper back then (nor now).

Can anybody explain these details for the >25MHz Silabs's?



List of 19 messages in thread
'51 derivatives cycle comparison table updated      Jan Waclawek      12/11/11 15:29      
   above about 40 Mhz devices may need extra cycles      Frieder Ferlemann      12/12/11 15:11      
      silabs with cache      Jan Waclawek      12/13/11 15:27      
         Ok, a SILabs cache lesson      Erik Malund      12/14/11 06:22      
            Bytes      Michael Karas      12/14/11 11:08      
               ecc?      Per Westermark      12/14/11 12:44      
               not the cookies      Erik Malund      12/15/11 07:17      
                  Washed?      Michael Karas      12/15/11 09:55      
                     am I as has happened before ...      Erik Malund      12/15/11 10:10      
                        Is that how it's spelled?      Richard Erlacher      12/15/11 12:52      
                     re: Washed?      Andy Peters      12/16/11 09:35      
            jump cache miss penalty      Jan Waclawek      12/15/11 00:35      
               clarifications      Erik Malund      12/15/11 07:33      
               no cache for 50MHz      Maarten Brock      12/15/11 16:01      
                  surely not all      Jan Waclawek      12/16/11 07:13      
                     you missed a word      Erik Malund      12/16/11 07:18      
   more update      Jan Waclawek      01/02/12 15:21      
      Table suggestions      Jim Granville      02/14/12 23:52      
      Updated MC51 supports Cycle Define      Jim Granville      04/26/12 16:17      

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