When I use $fopen to output a file in a simulation in ModelSim®, the number of files is limited to 30. What is the workaround?

<message>
Warning: (vsim-3533) [FOFIW] - No mcd channels available. Failed to open file ". /<filename> for writing.

Due to Verilog / language limitations, there is no tool workaround.

If you do not want to use the mcf functionality, as described in Knowledge below, try using file descriptor with type:
https://support.sw.siemens.com/ja-JP/product/852852093/ knowledge-base/MG60108

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category: simulation
tool: ModelSim®
device: -