![]() Difficulty with timing closure and accurate timing analysis. Not all FPGAs and ASIC cell libraries support asynchronous latches. If not, Quartus will generate asynchronous “latches”, which are BAD (and NOT ALLOWED for the RLE and SHA1 projects) !!Īsynchronous “latches” are BAD for the following reasons: Most (if not all) industry chip designs follow a “synchronous” design methodology where all flip-flops must be controlled by the same clock. ![]() Reg data type can be driven from initial. This implies that we are storing previous value, for which a latch is required. No condition of your code is satisfied, which means that the output will be unchanged. Consider the case when both the inputs a and b are 0. In a combinational always statement, and functions, “case” and “if-then-else” statements must be completely specified for all signals. Something that we need to know about reg is that it can be used for modeling both combinational and sequential logic. Inference: special patterns are detected in the language descriptionand treated specially (e.g. A latch is inferred when the output of combinatorial logic has undefined states, that is it must hold its previous value. This will synthesize to sequential logic. Each problem appears twice, rst without a solution, and in the second half of this le, with a solution. ![]() The problems have been selectedto cover important areas and are ordered from simple to more elaborate. Presentation on theme: "Problems with “Inferred Latches” in Verilog"- Presentation transcript:ġ Problems with “Inferred Latches” in Verilog This is a collection of EE 4755 solved problems related to sequential logic. ![]()
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