Nerd Ralph writes:
While writing the picoboot module for avrdude, I noticed avrdude has a terminal mode which allows for commands to be sent to an AVR. The serial programming interface for AVR MCUs uses SPI, similar to the nrf modules. I realized instead of an AVR, the programmer could be attached to any device that communicates via SPI. A couple hours later I had finished writing aspspi for avrdude – which permits a USBasp to be used for interactive SPI communication.