The Bung Game Master copier is special amongst all of the "NES era" copiers in that the games do not need to have their mapper writes modified to work with idiosyncratic copier mapper registers. Instead, the device has a Xilinx XC3042 FPGA that can emulate any NES-era mapper:
The FPGA bitstream data is included on the game disk itself for one-game mappers, while for standard mappers such as the MMC1 or MMC3, loading the game is preceded by loading the bitstream data from the appropriate mapper disk (called "preboot"), as this video demonstrates (preboot disk "M" is the disk for 256KiB PRG/128 KiB CHR MMC3).
A high-level emulation of this copier would be trivial by just reusing the normal MMC1 and MMC3 etc. emulation code. A true hardware-level emulation on the other hand would emulate the FPGA and make use of the bitstream data. I've read that the format of such bitstream data is undocumented, but given the age of that particular FPGA, I could imagine that its format has since been released or reverse-engineered, and emulators might even be available. I didn't find any, but maybe I didn't look in the right places?
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(Picture and info by Tomy)The FPGA bitstream data is included on the game disk itself for one-game mappers, while for standard mappers such as the MMC1 or MMC3, loading the game is preceded by loading the bitstream data from the appropriate mapper disk (called "preboot"), as this video demonstrates (preboot disk "M" is the disk for 256KiB PRG/128 KiB CHR MMC3).
A high-level emulation of this copier would be trivial by just reusing the normal MMC1 and MMC3 etc. emulation code. A true hardware-level emulation on the other hand would emulate the FPGA and make use of the bitstream data. I've read that the format of such bitstream data is undocumented, but given the age of that particular FPGA, I could imagine that its format has since been released or reverse-engineered, and emulators might even be available. I didn't find any, but maybe I didn't look in the right places?