There is also a way to work with the Teensy64 without an external drive.
My plan is to port the SD2IEC software to Teensy 3.6 and integrate it into "Teensy64".
SD2IEC can be connected to the interface of the board and works great. It seems to be a good replacement and emulates the floppy drive wonderfully. After some searching I found the "SD2IEC" project. However, a 1541 floppy disk drive that had been bought extra second-hand was damaged after a short time. Since the C64 operates this interface "in software" with the CPU and the signal lines have to be controlled more or less exactly in time, I couldn't find a way to keep the sound active even after many ideas and attempts.
For the serial floppy interface the SID sound emulation has to be switched off during the accesses, because reSID requires a lot of computing time. "Teensy64" is compatible enough to play many games and other programs like the original.
This goal has been achieved and I have the ambition to make some demos executable. In the beginning my goal was to make emulation good enough for "Boulder Dash" () and other of my old favorite games.
In the meantime I have rewritten the code for the VIC four times. But that was a good thing, otherwise I would never have started this project. I must admit that I have underestimated the VIC (the video chip of the C64) enormously. Unfortunately I forgot almost everything about the C64, and I had to and still have to learn everything anew and read a lot of technical details. After many preliminary considerations and deviations I came to the conclusion that the T3.6 should be capable of a C64 emulation. Paul Stoffregen thankfully provided me with an early pre-release version. After some attempts I had a working video player () - even before the official release of Teensy 3.6. Some time before, a user in the forum had noticed that you can overclock its SPi interface drastically. The first display that crossed my mind was the well-known ILI9341, which had already done a good job for the T3.2. However, the T3.6 has a fast SPI interface, which can be supplied via a DMA channel. There was no way to control a display fast enough. But before that, other hurdles had to be overcome. With 256KB RAM, more than enough flash, SD slot and 180 MHz it seemed possible to emulate a complete C64. Soon the wish for a SID-Player came up and a little later the Teensy 3.6 was announced. Unfortunately, current reSID versions require a lot of RAM, so I had to switch to an older version - which is not necessarily worse. It is even possible to emulate a second reSID for stereo operation. The porting () wasn't that difficult, but I've optimized some parts of it to better match the Teensy and its audio library. Since I had already had experience with the porting of audio codecs (mp3/aac/flac), I came up with the idea to search for a "finished" emulator and found the very good reSID. Some time ago, 2015, someone in the PJRC forum asked me if it was possible to emulate the C64's SID chip on the Teensy 3.2. Simple drive emulation included (load "whatever.prg" or load "$" ) Compatible to 1541 and other drives + SD2IEC