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2-Minute FPGAs: Blocking vs Nonblocking Statements in Verilog

Summer of FPGA
Blocking vs Nonblocking Statements in Verilog

FPGA Group | The Summer of FPGAs - Agenda

 

 

Join Whitney Knitter of Knitronics for two minutes as we discuss the logic and computer science behind programming with Lattice's ICE40 tinyFPGA! Today we discuss blocking vs nonblocking statements in Verilog! This's the first part in a series of videos and blog posts over the course of the Summer of FPGA.

 

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Additional Parts:

 

Product Name
iCE40 FPGAiCE40 FPGA
tinyFPGAtinyFPGA

 

Summer of FPGA 2-Minute FPGAs - More Videos Coming Soon!

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  • Great video Whitney !

    I have not written HDL in a very long time ...

    Back then, we called the two statements you described as combinatorial and sequential synchronous.
    Referring to your video:
    - non-blocking statement => combinatorial
    - blocking statement => sequential synchronous

    I agree that knowing the difference between the two is very important.

     

    Interestingly, back then, the language I coded with depended on my location:
    - when I worked on the west coast, I coded in Verilog

    - when I worked on the east coast, I coded in VHDL

    This may have must been coincidence, but was wondering if anyone else noticed this.

     

    Since I joined Avnet, I have been coding in both Verilog and VHDL.

    Again, have not touched these languages for quite a while now ... is anyone still using HDL languages ?

     

    Regards,

     

    Mario.

  • in reply to albertabeef

    "...Back then, we called the two statements you described as combinatorial and sequential..."

    I could potentially see mixing such terminology being confusing for those coming from a discrete logic background.

     

    Combinatorial/combinational logic in the discrete logic world would perhaps generally refer to logic where the output state would be dependent upon the input state at any given time. 

     

    Whereas sequential logic would perhaps generally refer to logic where the output state could depend not only on the current input state but also on the previous state, at the next clock cycle.

     

    So far the comparison holds out.

     

    However, in the video; at first glance, the logic diagram for blocking statements would perhaps appear to look more like combinatorial logic, whereas the logic diagram for non-blocking would perhaps appear to look more like sequential logic due to the addition of the clocks.

     

    Depending upon which way 'your brain is wired', then this logic perhaps may now appear to be inverted from discrete logic terminology.

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  • in reply to albertabeef

    "...Back then, we called the two statements you described as combinatorial and sequential..."

    I could potentially see mixing such terminology being confusing for those coming from a discrete logic background.

     

    Combinatorial/combinational logic in the discrete logic world would perhaps generally refer to logic where the output state would be dependent upon the input state at any given time. 

     

    Whereas sequential logic would perhaps generally refer to logic where the output state could depend not only on the current input state but also on the previous state, at the next clock cycle.

     

    So far the comparison holds out.

     

    However, in the video; at first glance, the logic diagram for blocking statements would perhaps appear to look more like combinatorial logic, whereas the logic diagram for non-blocking would perhaps appear to look more like sequential logic due to the addition of the clocks.

     

    Depending upon which way 'your brain is wired', then this logic perhaps may now appear to be inverted from discrete logic terminology.

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