Why verilog “always_comb block contains only one event control” error flagged on always procedural block with multiple “@”
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the following code below generates this error message:
"verilog always_comb imposes the restriction that it contains one and only one event control and no blocking timing controls"
always_comb begin
if (sig_a)begin
@(posedge sig_b); // wait for a sig_b posedge event
@(negedge sig_b); // then wait for a sig_b negedge event
event_true=1;
end
if (event_true)begin
@((sig_c==1)&&(sig_a==0)); //wait for sig_a to deassert and sig_c assert event to be true
yes =1;
end
else yes =0;
end
Why does the combi logic procedural block generate this error ?
And would an always block with @ event wait be synthesizable ?
verilog system-verilog hdl
asked Nov 16 '18 at 11:46
TheSprintingEngineerTheSprintingEngineer
4319
add a comment |
the following code below generates this error message:
"verilog always_comb imposes the restriction that it contains one and only one event control and no blocking timing controls"
always_comb begin
if (sig_a)begin
@(posedge sig_b); // wait for a sig_b posedge event
@(negedge sig_b); // then wait for a sig_b negedge event
event_true=1;
end
if (event_true)begin
@((sig_c==1)&&(sig_a==0)); //wait for sig_a to deassert and sig_c assert event to be true
yes =1;
end
else yes =0;
end
Why does the combi logic procedural block generate this error ?
And would an always block with @ event wait be synthesizable ?
verilog system-verilog hdl
asked Nov 16 '18 at 11:46
TheSprintingEngineerTheSprintingEngineer
4319
add a comment |
the following code below generates this error message:
"verilog always_comb imposes the restriction that it contains one and only one event control and no blocking timing controls"
always_comb begin
if (sig_a)begin
@(posedge sig_b); // wait for a sig_b posedge event
@(negedge sig_b); // then wait for a sig_b negedge event
event_true=1;
end
if (event_true)begin
@((sig_c==1)&&(sig_a==0)); //wait for sig_a to deassert and sig_c assert event to be true
yes =1;
end
else yes =0;
end
Why does the combi logic procedural block generate this error ?
And would an always block with @ event wait be synthesizable ?
verilog system-verilog hdl
asked Nov 16 '18 at 11:46
TheSprintingEngineerTheSprintingEngineer
4319
the following code below generates this error message:
"verilog always_comb imposes the restriction that it contains one and only one event control and no blocking timing controls"
always_comb begin
if (sig_a)begin
@(posedge sig_b); // wait for a sig_b posedge event
@(negedge sig_b); // then wait for a sig_b negedge event
event_true=1;
end
if (event_true)begin
@((sig_c==1)&&(sig_a==0)); //wait for sig_a to deassert and sig_c assert event to be true
yes =1;
end
else yes =0;
end
Why does the combi logic procedural block generate this error ?
And would an always block with @ event wait be synthesizable ?
verilog system-verilog hdl
verilog system-verilog hdl
asked Nov 16 '18 at 11:46
TheSprintingEngineerTheSprintingEngineer
4319
asked Nov 16 '18 at 11:46
TheSprintingEngineerTheSprintingEngineer
4319
asked Nov 16 '18 at 11:46
TheSprintingEngineerTheSprintingEngineer
4319
asked Nov 16 '18 at 11:46
TheSprintingEngineerTheSprintingEngineer
4319
asked Nov 16 '18 at 11:46
TheSprintingEngineerTheSprintingEngineer
4319
4319
add a comment |
add a comment |
2 Answers
2
active
oldest
votes
The message reported by that error is misleading. You are not allowed ANY event controls in an always_comb block. It creates the event sensitivity list automatically for you. Maybe it is combining the implicit event control with the ones you added to it, then generating the error.
Unless you are using a high-level synthesis tool, you are restricted to having one event control at the beginning of a basic always block.
answered Nov 16 '18 at 15:45
dave_59dave_59
20.9k21639
I'm using VCS, it might allow multiple@event trigger to function as a wait in one always block (not so sure, how do i check for this ?). Anyhow, so say if I replacedalways_combwithalwaysin my code, would the syntax that follow, be allowed? As in multiple event controls@ (posedge sig_b)and@(negedge sig_b)in one always block as shown here in link
– TheSprintingEngineer
Nov 18 '18 at 15:22
1
Simulators allow more syntax than what is synthesizable.
– dave_59
Nov 18 '18 at 16:02
add a comment |
always_comb is for combinational logic only. the @ statements you use have nothing to do with combinational.
from lrm 9.2.2.2.2
Statements in an always_comb shall not include those that block, have blocking timing or event controls, or fork-join statements.
In your case you need to use a general purpose always. always @* will probably do.
answered Nov 16 '18 at 12:18
SergeSerge
4,13721016
add a comment |
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2 Answers
2
active
oldest
votes
2 Answers
2
active
oldest
votes
active
oldest
votes
active
oldest
votes
The message reported by that error is misleading. You are not allowed ANY event controls in an always_comb block. It creates the event sensitivity list automatically for you. Maybe it is combining the implicit event control with the ones you added to it, then generating the error.
Unless you are using a high-level synthesis tool, you are restricted to having one event control at the beginning of a basic always block.
answered Nov 16 '18 at 15:45
dave_59dave_59
20.9k21639
I'm using VCS, it might allow multiple@event trigger to function as a wait in one always block (not so sure, how do i check for this ?). Anyhow, so say if I replacedalways_combwithalwaysin my code, would the syntax that follow, be allowed? As in multiple event controls@ (posedge sig_b)and@(negedge sig_b)in one always block as shown here in link
– TheSprintingEngineer
Nov 18 '18 at 15:22
1
Simulators allow more syntax than what is synthesizable.
– dave_59
Nov 18 '18 at 16:02
add a comment |
The message reported by that error is misleading. You are not allowed ANY event controls in an always_comb block. It creates the event sensitivity list automatically for you. Maybe it is combining the implicit event control with the ones you added to it, then generating the error.
Unless you are using a high-level synthesis tool, you are restricted to having one event control at the beginning of a basic always block.
answered Nov 16 '18 at 15:45
dave_59dave_59
20.9k21639
I'm using VCS, it might allow multiple@event trigger to function as a wait in one always block (not so sure, how do i check for this ?). Anyhow, so say if I replacedalways_combwithalwaysin my code, would the syntax that follow, be allowed? As in multiple event controls@ (posedge sig_b)and@(negedge sig_b)in one always block as shown here in link
– TheSprintingEngineer
Nov 18 '18 at 15:22
1
Simulators allow more syntax than what is synthesizable.
– dave_59
Nov 18 '18 at 16:02
add a comment |
The message reported by that error is misleading. You are not allowed ANY event controls in an always_comb block. It creates the event sensitivity list automatically for you. Maybe it is combining the implicit event control with the ones you added to it, then generating the error.
Unless you are using a high-level synthesis tool, you are restricted to having one event control at the beginning of a basic always block.
answered Nov 16 '18 at 15:45
dave_59dave_59
20.9k21639
The message reported by that error is misleading. You are not allowed ANY event controls in an always_comb block. It creates the event sensitivity list automatically for you. Maybe it is combining the implicit event control with the ones you added to it, then generating the error.
Unless you are using a high-level synthesis tool, you are restricted to having one event control at the beginning of a basic always block.
answered Nov 16 '18 at 15:45
dave_59dave_59
20.9k21639
answered Nov 16 '18 at 15:45
dave_59dave_59
20.9k21639
answered Nov 16 '18 at 15:45
dave_59dave_59
20.9k21639
answered Nov 16 '18 at 15:45
dave_59dave_59
20.9k21639
20.9k21639
I'm using VCS, it might allow multiple@event trigger to function as a wait in one always block (not so sure, how do i check for this ?). Anyhow, so say if I replacedalways_combwithalwaysin my code, would the syntax that follow, be allowed? As in multiple event controls@ (posedge sig_b)and@(negedge sig_b)in one always block as shown here in link
– TheSprintingEngineer
Nov 18 '18 at 15:22
1
Simulators allow more syntax than what is synthesizable.
– dave_59
Nov 18 '18 at 16:02
add a comment |
I'm using VCS, it might allow multiple@event trigger to function as a wait in one always block (not so sure, how do i check for this ?). Anyhow, so say if I replacedalways_combwithalwaysin my code, would the syntax that follow, be allowed? As in multiple event controls@ (posedge sig_b)and@(negedge sig_b)in one always block as shown here in link
– TheSprintingEngineer
Nov 18 '18 at 15:22
1
Simulators allow more syntax than what is synthesizable.
– dave_59
Nov 18 '18 at 16:02
I'm using VCS, it might allow multiple
@ event trigger to function as a wait in one always block (not so sure, how do i check for this ?). Anyhow, so say if I replaced always_comb with always in my code, would the syntax that follow, be allowed? As in multiple event controls @ (posedge sig_b) and @(negedge sig_b) in one always block as shown here in link– TheSprintingEngineer
Nov 18 '18 at 15:22
I'm using VCS, it might allow multiple
@ event trigger to function as a wait in one always block (not so sure, how do i check for this ?). Anyhow, so say if I replaced always_comb with always in my code, would the syntax that follow, be allowed? As in multiple event controls @ (posedge sig_b) and @(negedge sig_b) in one always block as shown here in link– TheSprintingEngineer
Nov 18 '18 at 15:22
1
1
Simulators allow more syntax than what is synthesizable.
– dave_59
Nov 18 '18 at 16:02
Simulators allow more syntax than what is synthesizable.
– dave_59
Nov 18 '18 at 16:02
add a comment |
always_comb is for combinational logic only. the @ statements you use have nothing to do with combinational.
from lrm 9.2.2.2.2
Statements in an always_comb shall not include those that block, have blocking timing or event controls, or fork-join statements.
In your case you need to use a general purpose always. always @* will probably do.
answered Nov 16 '18 at 12:18
SergeSerge
4,13721016
add a comment |
always_comb is for combinational logic only. the @ statements you use have nothing to do with combinational.
from lrm 9.2.2.2.2
Statements in an always_comb shall not include those that block, have blocking timing or event controls, or fork-join statements.
In your case you need to use a general purpose always. always @* will probably do.
answered Nov 16 '18 at 12:18
SergeSerge
4,13721016
add a comment |
always_comb is for combinational logic only. the @ statements you use have nothing to do with combinational.
from lrm 9.2.2.2.2
Statements in an always_comb shall not include those that block, have blocking timing or event controls, or fork-join statements.
In your case you need to use a general purpose always. always @* will probably do.
answered Nov 16 '18 at 12:18
SergeSerge
4,13721016
always_comb is for combinational logic only. the @ statements you use have nothing to do with combinational.
from lrm 9.2.2.2.2
Statements in an always_comb shall not include those that block, have blocking timing or event controls, or fork-join statements.
In your case you need to use a general purpose always. always @* will probably do.
answered Nov 16 '18 at 12:18
SergeSerge
4,13721016
answered Nov 16 '18 at 12:18
SergeSerge
4,13721016
answered Nov 16 '18 at 12:18
SergeSerge
4,13721016
answered Nov 16 '18 at 12:18
SergeSerge
4,13721016
4,13721016
add a comment |
add a comment |
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