For any USBasp user I would greatly recommend looking at alternative firmware set: USB AVR Lab. This software increases USBasp capabilities allowing to switch its firmware almost instantly and reusing hardware. It creates kind of "software defined" lab tool (hence the name) that can function as:
- AVR programmer with either original USBasp firmware, AVRISPmkII, STK500v2 or JTAGICEmkII emulation,
- JTAG/OpenOCD interface (unfortunately: still alpha),
- generic USB to digital I/O interface,
- digital sniffer supporting SPI, UART and I2C protocols,
- most impressive in my opinion: low-speed digital oscilloscope (230 kSps).