It would be nice if the SDIO pins were defined for this variant like other variants. A pinout diagram is here. I think this is the correct definition. // SDIO #define PIN_SD_CLK (18u) #define ...

You can build a simple programmer using popular FT232RL breakout boards (search Ebay for "FT232RL adapter" for example). Pinout specified in spi.c file. Change it at will. Note that FTDI boards ...