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We can do this directly from a parallel port – - this just involves connecting the right pins on the parallel port to the right pins on the Mini:

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It is possible to use dasa with a USB-to-serial converter, but the performance is very slow[1]. It is possible to use dapa with a USB-to-parallel converter, but the performance will be equally slow. In addition, I've heard the claim that some USB-to-parallel converters are meant solely to drive printers, and do not implement full parallel port functionality, and so would not work.

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usbspeed usbspeed

USB is moderately high latency (the numbers I've seen for low latency USB devices are order of magnitude is 1-30 ms, depending on device). Assuming AVRDude waits for each operation to finish before the next one, sending one bit requires 3 bit flips (3-90 ms). Sending one byte requires 24 bit flips (24-720ms). This gives ballpark of 1-42 bytes/second. What I saw when using a dasa cable with a USB-to-serial converter (5 bytes/second) was close to the middle of that, so I believe that was my
problem. The adapter uses an FTDI USB-to-serial chip, most of which are designed to also be able to bit bang with the RS232 control pins, so I doubt choice of dasa lines was the problem – - it ought to be able to flip all of them comparably quickly. The same dasa adapter worked at normal speed when it used an actual motherboard with a serial port.