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???
04/20/07 05:40
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 		 #137592 - The point is i think ... unitentional latches
Responding to: ???'s previous message
There are several ways in which it is possible to infer a latch when it wasnt intentional so if the tools didnt shout about it then people would be complaining that their designs didnt work.
The classic way to mistakenly infer a latch is to have an 'if' statement without an 'else' as in Andy's example.So its not so much a warning about the metastability issues, because most compilers wont actualy let you construct a latch with a combinatioanl feedback loop but always insert their own latch macro, its just a warning against unitentional ones.

List of 54 messages in thread
TopicAuthorDate
VHDL FPGA            01/01/70 00:00      
   Hello, world?            01/01/70 00:00      
      LCD display            01/01/70 00:00      
         video overlay            01/01/70 00:00      
            funny you should say that            01/01/70 00:00      
   bcd to binary            01/01/70 00:00      
      Try a different algorithm            01/01/70 00:00      
      easier way            01/01/70 00:00      
         LUT            01/01/70 00:00      
   This is what you want!            01/01/70 00:00      
      It is not as easy as it seems!            01/01/70 00:00      
   Here\'s a little exercise ...            01/01/70 00:00      
      more info required            01/01/70 00:00      
         I don't think its very fair.            01/01/70 00:00      
            consider this ...            01/01/70 00:00      
         pick an arbitrary frequency            01/01/70 00:00      
   warnings            01/01/70 00:00      
      Give us a clue,what do they say?            01/01/70 00:00      
         warnings sample            01/01/70 00:00      
            You can ignore most of them, but Quartus is buggy            01/01/70 00:00      
               Combinational Loops            01/01/70 00:00      
                  No doubt about it ...            01/01/70 00:00      
            gated/ripple clocks            01/01/70 00:00      
               ... but those complaints aren\'t always relevant            01/01/70 00:00      
            warnings            01/01/70 00:00      
               Andy, how would YOU construct a latch?            01/01/70 00:00      
                  latches in FPGAs            01/01/70 00:00      
                     Excellent Posting            01/01/70 00:00      
                     more about latches            01/01/70 00:00      
                        I like clear terms in my latches            01/01/70 00:00      
                           The point is i think ... unitentional latches            01/01/70 00:00      
                              exactly ...            01/01/70 00:00      
                                 elsif            01/01/70 00:00      
                                    Bad code            01/01/70 00:00      
                                    elsif            01/01/70 00:00      
                                 Quartus complains if you use the library latch            01/01/70 00:00      
                           latch reset inputs            01/01/70 00:00      
                              the library latch has no clear function            01/01/70 00:00      
                                 Brand A vs Brand X            01/01/70 00:00      
                                    true enough            01/01/70 00:00      
   Modelsim            01/01/70 00:00      
      about the only limitations on modelsim are ;-            01/01/70 00:00      
      ModelSim, PicoBlaze, MicroBlaze            01/01/70 00:00      
         there's a CPLD <=>LCD app note            01/01/70 00:00      
            JTAG interface            01/01/70 00:00      
            darn            01/01/70 00:00      
               Xilinx CPLD applications handbook            01/01/70 00:00      
   Mahmood, stick with the recommended circuit            01/01/70 00:00      
      Recommended circuit            01/01/70 00:00      
         I would be really careful ...            01/01/70 00:00      
            Thanks Richard            01/01/70 00:00      
               don't be distracted by the unnecessary parts            01/01/70 00:00      
                  Xilinx Jtag for Altera            01/01/70 00:00      
                     How about Altera JTAG for ALTERA            01/01/70 00:00      

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