Convert severity tasks to Verilog

sifferman commented 5 months ago

Hello!

SystemVerilog added the system tasks $fatal, $error, $warning, and $info (20.10). However, sv2v does not convert them at all, causing Verilog tools to fail. It would be nice to convert them into Verilog-2005 tasks so that they can still be used in pure Verilog tools.

This is my interpretation of the LRM:

$error, $warning, and $info should all be turned into $display.
$fatal should first run a $display, then run $finish

This is a description of what should go in the $display:

[Each task should include a tool-specific message with] the following information:

The file name and line number of the severity system task call. The file name and line number shall be the same as `__FILE__ and `__LINE__ compiler directives, respectively.

The hierarchical name of the scope in which the severity system task call is made.

For simulation tools, the simulation run time at which the severity system task is called. The tool-specific message shall include the user-defined message if specified.

It could be helpful to have `__FILE__ and `__LINE__ for both the inputted .sv file and the outputted .v file. Verilog-2005 has no `__FILE__ equivalent, but it does have `line (19.7).

I would be happy to look into this if you'd like. :)

sifferman commented 5 months ago

I ran this example through the big 4 to see what the outputs should be:

module tb;
    initial begin
        $info;
        $info("%b", 1);
        $warning;
        $warning("%b", 2);
        $error;
        $error("%b", 3);
        // $fatal;
        // $fatal(0, "%b", 4);
        // showing results from both fatal calls if each were run individually
    end
endmodule

VCS

Info: "tb.sv", 3: tb: at time 0

Info: "tb.sv", 5: tb: at time 0
00000000000000000000000000000001

Warning: "tb.sv", 7: tb: at time 0

Warning: "tb.sv", 9: tb: at time 0
00000000000000000000000000000010

Error: "tb.sv", 11: tb: at time 0

Error: "tb.sv", 13: tb: at time 0
00000000000000000000000000000011

Fatal: "tb.sv", 15: tb: at time 0

Fatal: "tb.sv", 17: tb: at time 0
00000000000000000000000000000100

ModelSim

# ** Info: Assertion error.
#    Time: 0 ns  Scope: tb File: tb.sv Line: 3
# 
# ** Info: 00000000000000000000000000000001
#    Time: 0 ns  Scope: tb File: tb.sv Line: 5
# 
# ** Warning: Assertion error.
#    Time: 0 ns  Scope: tb File: tb.sv Line: 7
# 
# ** Warning: 00000000000000000000000000000010
#    Time: 0 ns  Scope: tb File: tb.sv Line: 9
# 
# ** Error: Assertion error.
#    Time: 0 ns  Scope: tb File: tb.sv Line: 11
# 
# ** Error: 00000000000000000000000000000011
#    Time: 0 ns  Scope: tb File: tb.sv Line: 13
# 
# ** Fatal: Assertion error.
#    Time: 0 ns  Scope: tb File: tb.sv Line: 15
# 
# ** Fatal: 00000000000000000000000000000100
#    Time: 0 ns  Scope: tb File: tb.sv Line: 17

Xcelium

xmsim: *N,INFSEV (./tb.sv,3): (time 0 FS).
tb

xmsim: *N,INFSEV (./tb.sv,5): (time 0 FS).
tb
00000000000000000000000000000001

xmsim: *W,WARSEV (./tb.sv,7): (time 0 FS).
tb

xmsim: *W,WARSEV (./tb.sv,9): (time 0 FS).
tb
00000000000000000000000000000010

xmsim: *E,ERRSEV (./tb.sv,11): (time 0 FS).
tb

xmsim: *E,ERRSEV (./tb.sv,13): (time 0 FS).
tb
00000000000000000000000000000011

xmsim: *F,FATSEV (./tb.sv,15): (time 0 FS).
tb

xmsim: *F,FATSEV (./tb.sv,17): (time 0 FS).
tb
00000000000000000000000000000100

Verilator

[0] -Info: tb.sv:3: TOP.tb

[0] -Info: tb.sv:5: TOP.tb: 00000000000000000000000000000001

[0] %Warning: tb.sv:7: TOP.tb

[0] %Warning: tb.sv:9: TOP.tb: 00000000000000000000000000000010

[0] %Error: tb.sv:11: Assertion failed in TOP.tb

[0] %Error: tb.sv:13: Assertion failed in TOP.tb: 00000000000000000000000000000011

[0] %Fatal: tb.sv:15: Assertion failed in TOP.tb

[0] %Fatal: tb.sv:17: Assertion failed in TOP.tb: 00000000000000000000000000000100

(Note that this run required the use of +verilator+error+limit+3. I think this is kind of a cool feature, and I wonder if it could be feasible to do something like $value$plusargs("sv2v+error+limit+%d", _sv2v_error_limit). Just a thought...)

Summary

This is what I'm thinking:

$info(message);

$display("[%t] Info: %s", $time, message);
$display("Src File: <PRE_SV2V_FILENAME>:<PRE_SV2V_LINE>, Scope: <PRE_SV2V_SCOPE>");
$display("Sv2v File: <POST_SV2V_FILENAME>:%s, Scope: <POST_SV2V_SCOPE>", "<POST_SV2V_LINE>");

<POST_SV2V_FILENAME> can be collected from sv2v --write
<POST_SV2V_LINE> can be collected from 1364 19.7 `line
<POST_SV2V_SCOPE> can be precomputed by sv2v

for example:

[10] Info: Handshake received.
Src File: rtl/com.sv:43, Scope: top.com
Sv2v File: sv2v.v:126, Scope: top.com

zachjs commented 5 months ago

I'm very interested in getting this enhancement in, and greatly appreciate your initiative in filing a PR. Thank you!

I think I'm missing an important piece of context: What tools don't support the SystemVerilog severity tasks? I know iverilog and Yosys do. Verilator does, but only in SystemVerilog mode. You've got a good sampling of the commercial simulators here, too. What tool are you using in your flow that doesn't support them?

sifferman commented 5 months ago

As far as I can tell, all commercial tools support the SystemVerilog severity tasks only when in SystemVerilog mode. And I wasn't aware that Yosys had support. So I don't believe that it is crucial for this issue to be completed. Plus, if a tool natively supports SystemVerilog severity tasks, it likely can provide more helpful warnings than what sv2v can offer.

But this change would bring sv2v closer to full 1800→1364 conversion. So I would say it is up to you on whether this change should be used. :smiley:

zachjs / sv2v