The Universal Serial Bus protocol is used to connect many different devices to a computer, such as keyboards, mice, CD readers, video cameras and audio ports.
The Mizar32 has a micro OTG (On-The-Go) USB socket which can act as a USB device to be seen by an external computer, or as a USB master to talk with USB devices.
You can't program the USB subsystem directly from Alcor6L. Instead, it contains software that pretends to be a USB serial port which is connected to the Alcor6L console in the SimpleMachines firmware releases from 2013 onwards (before that, the console was connected to a real serial port on the Mizar32 RS232 UART add-on hardware module.)
On a GNU/Linux PC, you can use the minicom terminal to talk to Alcor6L's USB serial port, specifying the serial device as /dev/ttyACM0. When it's talking to a GNU/Linux-based operating system it takes about 8 seconds for the Mizar32 and the PC to start talking to one another after you power the Mizar32 on.
On Windows it should appear as a USB serial device when you plug it in and you can use the PuTTY terminal emulator to talk to it but the whole system hangs if you reset or power-cycle the Mizar32. To get the Mizar32 and Windows talking to each other again, a Windows user writes:
"In Win, for the USB CDC to be recognised, you must disconnect it from Mizar32, close the terminal ["putty"], reconnect Mizar32, reopen the terminal. If you press Reset on the Mizar32, you must disconnect the Mizar32 from the usb, close the terminal, reconnect the Mizar32, re-open the terminal."
You can compile custom firmware at http://builder.simplemachines.it placing the console on a real serial port or on telnet, leaving the USB system free from interference from console output. In this case it can be used like any other serial port by passing serial port number 176 to eLua's uart.*() functions.
As used by the DFU boot loader
When the Device Firmware Upgrade Boot Loader software is activated, it also uses the USB port to talk to your PC, but not as a USB serial port. Instead, it emulates a special Atmel device which speaks the DFU firmware-updating language and requires special software on the attached PC, such as
batchisp3. See the Advanced Topic on flashing firmware to the Mizar32 with the DFU bootloader.