This USBasp firmware is based on a fork by Ralph Doncaster. Original fork readme can be found at README_nerdralph.md.
- From version 1.07 a default SCK clock of 1.5Mhz and automatic SCK slowing if target does not respond. PORTD is left as input, so this firmware also works with USBISP modules. ( nerdralph )
- From version 1.08 the firmware is WCID compliant, meaning it should work on Windows without any driver or .inf install.
- From version 1.09 a slow ( 4800 Baud ) UART HID implementation will be added for debugging purposes. USBasp will appear as a composite device with a WINUSB interface and a HID interface.
Note: A pre-built hex file for the mega8 (main.hex) is in the firmware directory, along with m88.hex for the mega88.
Pre-built avrdude 6.3 and 6.4, windows executables, if needed, is in the bin\avrdude-winusb directory. Build with MSYS2 and avr8-gnu-toolchain (3.6.2.17778) from Microchip, on a Windows 10 box.
UART HID implemention uses 8 byte size input and output reports. The last byte holds the actual serial bytes count. The remaining bytes are ignored.
i.e. Input or Output Report
0x55,0x34,0x00,0x00,0x00,0x00,0x00,0x02 -> Actual serial bytes 2 : 0x55,0x34
0x00,0x34,0x00,0x66,0x32,0x36,0x00,0x04 -> Actual serial bytes 4 : 0x00,0x34,0x00,0x66The USBasp's UART configuration uses a 1 byte size feature report, with the following format.
| Byte 0 | Byte 1 | Byte 2 | Byte 3 | Byte 4 - 7 RO |
|---|---|---|---|---|
| Prescaler Low Byte | Prescaler High Byte | See UART Flags | Unused | USBasp Capabilities |
To setup and enable the UART, send a feature set report, with the prescaler in the first two bytes and the parity, data bit, stop bit flags at the third byte ( see UART Flags ). The fourth byte is ignored.
To disable the UART, send a feature set report, with the prescaler bytes as zero.
Note: The UART is disabled by default, if read or write is detected for do to not interfere with those functions.