The original author of usbasp is Thomas Fischl. My m32 firmware is forked from bperrybap, his modification is very stable and fast.
The hardware change is not much, apart from upgrading m8 to m32, the two LED is changed from PC0,PC1 to PC4 and PC5. JP3 is removed also.
To build the firmware, assuming the build envionment is ready, just navigate to firmware folder and "make hex".