I am just beginning my first USB design. I plan to use an AVR with built in USB like ATmega32U6 but I could maybe also use a software solution like vUSB but it may be too slow, I need to transfer 1 Gbit from a flash memory in a reasonable time. The design do only need to be able to put into a computer for download of the file so endpoint mode should be enough.
But I need to know if I need to use a crystal or if I can use the internal RC oscillator. And what speed must it be. Power consumption at the time it is not connected to the computer is very critical and the RC oscillator have much faster start-up time (it will use 32 kHz crystal and power up once a second) and therefore it may be to prefer if possible. Speed also depend on what is possible for the voltage. 3V is again best for power consumption but maybe I must use higher for clock speed demands of the USB.
Any information about the clock/voltage/USB is