The TeensyROM is a Commodore 64 ROM emulator and loader/interface cartridge, designed by Travis Smith (travis@sensoriumembedded.com), and is based on the Teensy 4.1. It offers immediate loading, emulation, and running of files from USB thumb drives, SD cards, or the internal flash of the Teensy board. Additionally, by including a C# Windows desktop application with the product, it is possible to transfer files directly from a PC for use on the emulator.
Apart from that, this cartridge also has the ability to set a system time from an Ethernet connection and to emulate 8KHi/Lo/16K .crt files and run .prg files too. The initial printed circuit board version 0.1 has been completed and tested – although some changes still may be made in future iterations such as integrating Ethernet and USB host connectors in order to eliminate the need for dongles when using this piece of hardware. So far only NTSC C64 machines have been tested with this device but compatibility tests may still continue on other variants later on.
For more information check out the TeensyROM page on GitHub.