Atomic Counters in VHDL

library IEEE;
use IEEE.STD_LOGIC_1164.ALL;
use IEEE.NUMERIC_STD.ALL;

entity AtomicCounter is
end AtomicCounter;

architecture Behavioral of AtomicCounter is
    signal counter : unsigned(63 downto 0) := (others => '0');
begin
    process
        variable local_counter : unsigned(63 downto 0) := (others => '0');
    begin
        -- Simulate 50 concurrent processes
        for i in 1 to 50 loop
            -- Each process increments the counter 1000 times
            for j in 1 to 1000 loop
                -- Read the current value
                local_counter := counter;
                -- Increment
                local_counter := local_counter + 1;
                -- Write back the new value
                counter <= local_counter;
                -- This is not truly atomic, but simulates the concept
                wait for 1 ns;
            end loop;
        end loop;
        
        -- Print the final result
        report "Counter value: " & integer'image(to_integer(counter));
        wait;
    end process;
end Behavioral;

In VHDL, we don’t have direct equivalents for goroutines or atomic operations as in high-level programming languages. However, we can simulate the concept using a process and signals.

The primary mechanism for managing state in VHDL is through signals and processes. In this example, we’re simulating atomic counters accessed by multiple concurrent operations.

We define a 64-bit unsigned signal counter to represent our always-positive counter.

The main process simulates 50 concurrent operations, each incrementing the counter 1000 times. In each iteration:

1. We read the current counter value into a local variable.
2. We increment the local variable.
3. We write the new value back to the counter signal.
4. We wait for 1 ns to simulate the passage of time and allow for signal updates.

This is not truly atomic as in software languages, but it simulates the concept of multiple processes accessing and updating a shared counter.

After all iterations, we report the final counter value.

To run this VHDL code, you would typically use a VHDL simulator like ModelSim or GHDL. The simulation would show the counter incrementing over time, and the final value should be 50,000, matching the expected result from the original Go example.

Note that VHDL is typically used for hardware description and simulation, so concepts like goroutines and atomic operations don’t have direct equivalents. This example demonstrates a simplified simulation of the concept in a hardware context.