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verilator/test_regress/t/t_timing_fork_unsup.v

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Timing support (#3363) Adds timing support to Verilator. It makes it possible to use delays, event controls within processes (not just at the start), wait statements, and forks. Building a design with those constructs requires a compiler that supports C++20 coroutines (GCC 10, Clang 5). The basic idea is to have processes and tasks with delays/event controls implemented as C++20 coroutines. This allows us to suspend and resume them at any time. There are five main runtime classes responsible for managing suspended coroutines: * `VlCoroutineHandle`, a wrapper over C++20's `std::coroutine_handle` with move semantics and automatic cleanup. * `VlDelayScheduler`, for coroutines suspended by delays. It resumes them at a proper simulation time. * `VlTriggerScheduler`, for coroutines suspended by event controls. It resumes them if its corresponding trigger was set. * `VlForkSync`, used for syncing `fork..join` and `fork..join_any` blocks. * `VlCoroutine`, the return type of all verilated coroutines. It allows for suspending a stack of coroutines (normally, C++ coroutines are stackless). There is a new visitor in `V3Timing.cpp` which: * scales delays according to the timescale, * simplifies intra-assignment timing controls and net delays into regular timing controls and assignments, * simplifies wait statements into loops with event controls, * marks processes and tasks with timing controls in them as suspendable, * creates delay, trigger scheduler, and fork sync variables, * transforms timing controls and fork joins into C++ awaits There are new functions in `V3SchedTiming.cpp` (used by `V3Sched.cpp`) that integrate static scheduling with timing. This involves providing external domains for variables, so that the necessary combinational logic gets triggered after coroutine resumption, as well as statements that need to be injected into the design eval function to perform this resumption at the correct time. There is also a function that transforms forked processes into separate functions. See the comments in `verilated_timing.h`, `verilated_timing.cpp`, `V3Timing.cpp`, and `V3SchedTiming.cpp`, as well as the internals documentation for more details. Signed-off-by: Krzysztof Bieganski <kbieganski@antmicro.com>
2022-08-22 12:26:32 +00:00
// DESCRIPTION: Verilator: Verilog Test module
//
// This file ONLY is placed under the Creative Commons Public Domain, for
// any use, without warranty, 2022 by Antmicro Ltd.
// SPDX-License-Identifier: CC0-1.0
module t;
class C;
task f;
int x = 0;
fork
#6 x = 4;
#2 x++;
x = #4 x * 3;
begin
#1 if (x != 1) $stop;
#2 if (x != 2) $stop;
#2 if (x != 3) $stop;
#2 if (x != 4) $stop;
$finish;
end
join_none
x = 1;
endtask
endclass
initial begin
C o = new;
o.f;
end
endmodule
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