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Altera_Forum's avatar
Altera_Forum
Icon for Honored Contributor rankHonored Contributor
16 years ago

why the simulation result is differenct between fork join and begin end?

this is the testbench in an495.

why can not use begin ... end.

initial

begin

arst <= 1'b0; // resetting the contoller initially

# 250

arst <= 1'b1;

iderst <= 1'b0;

ideen <= 1'b1;

pioiordyen <= 1'b1;

piorqst <= 1'b1;

pioaddr <= 4'b0111;

piodatain <= 16'b1111111100000000;

piowe <= 1'b1;

# 600 piowe <= 1'b0;

ddi <= 16'b0000000011111111;

iordy <= 1'b1;

intrq <= 1'b1;

flag <= 1'b0; //if error occured in the test procedure,then asserted

# 5000

$stop;

end

use the fork join,the result is right

fork

arst = 1'b0; // resetting the contoller initially

# 250

arst = 1'b1;

iderst = 1'b0;

ideen = 1'b1;

pioiordyen = 1'b1;

piorqst = 1'b1;

pioaddr = 4'b0111;

piodatain = 16'b1111111100000000;

piowe = 1'b1;

# 600 piowe = 1'b0;

ddi = 16'b0000000011111111;

iordy = 1'b1;

intrq = 1'b1;

flag = 1'b0; //if error occured in the test procedure,then asserted

# 5000

$stop;

join

2 Replies

  • Altera_Forum's avatar
    Altera_Forum
    Icon for Honored Contributor rankHonored Contributor
    16 years ago

    The difference between "begin-end" and "fork-join" is that in initial block "begin-end" operations work step-by-step, but in "fork-join" they work simultaneously. You can rewrite the testbench using "begin-end". For example,

    begin

    arst <= 1'b0; // resetting the contoller initially

    iderst <= 1'b0;

    ideen <= 1'b1;

    pioiordyen <= 1'b1;

    piorqst <= 1'b1;

    pioaddr <= 4'b0111;

    piodatain <= 16'b1111111100000000;

    piowe <= 1'b1;

    iordy <= 1'b1;

    intrq <= 1'b1;

    flag <= 1'b0; //if error occured in the test procedure,then asserted

    ddi <= 16'b0000000011111111;

    # 250 arst <= 1'b1;

    # 350 piowe <= 1'b0;

    # 4400 $stop;

    end

    I believe, it will work like original "fork-join"
  • Altera_Forum's avatar
    Altera_Forum
    Icon for Honored Contributor rankHonored Contributor
    16 years ago

    The begin-end-block also assigns the values to the nets simultaneously if non-blocking assignments are used (as it's the case in the example). The difference is that all timing assignments are with respect to the block entry time in case of fork-join and with respect to the previous timing assignment in case of begin-end.