ATmega8U2 core?

I would find it to be a big advantage if I could use the ATmega8U2 as a serial <> usb adapter while also running personal arduino code, nothing resource heavy, just read serial, plop out to 74HC595

right now I am using FTDI cable > attiny85 > SR to accomplish the same thing, and well its frankly cheaper and tidier if I could save the whole FTDI + avr combo

if not … looks like I will be taking a dive into LUFA and AVR Studio this holiday weekend.

Does LUFA support a s/w based USB?

Sounds like V-USB might be the ticket.

See the projects links for examples.
There are some pretty neat projects out there.
There is also the AVR-CDC stuff that might also be useful:

This level work definitely requires that you leave Arduino and its IDE
behind for development.

Here are few other links that might be interesting:

--- bill

I vaguely recall that the ATmega8U2 is pretty full-up.

I was assuming continuing to use the attiny85 but with s/w based USB so the FTDI cable could
go away.

--- bill

either way, looking at a baud rate of 9600


This link is related to changing the program in Atmega8U2, maybe it will help you.

either way, looking at a baud rate of 9600

Baud rate is meaningless when using a virtual serial connection over USB
when using native USB since there is no actual asynchronous serial connection.

It would be USB->attiny85->Shiftregister.

Baud rate is still there and "can be set" since it is part of the virtual com protocol,
but it doesn't really do anything or affect the actual data transfer rate.

The data rate will be throttled by USB and the speed of the USB s/w in the attiny.

--- bill