GHDL is free simulator. I found this tool very useful. GHDL is also capable simulating the free LEON processor. Presently, if the VCD option is enabled, all signals of the design are recorded. This impacts the performance and requires large disk space.
I generate my own form the VHDL code (example: probe_i2c_slv.vhd). This way it is easy to select what signals to dump and on what time. More details are at :
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