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I think Osamu has some statistics included with his AVR-CDC project.

As you already found out: We take great care to ensure that newer versions have the same or less code size than previous versions. Regarding VID/PID: We added a warning if it's not defined in usbconfig.h because we want to make sure that people know what they are doing. Simply add obdev's free VID/P...

Please measure the voltage level on D- when the device is idle. It should be well above 2.5 V and below 3.6 V. Some Zener diodes are not suitable.

This is an old note. Recent versions of AVR-USB don't have this requirement any more.

If the boot loader fails to work, please check the usual things: fuses, speed selection in usbconfig.h, level conversion for D+ and D- etc.

You need to detect the Start Of Frame pulses. Since they are on D-, you need to supervise D-. The pulses are short (667 ns) and rare (every 1 ms), so you need hardware to detect them. This hardware could be an interrupt or a counter input. There are no such pulses on D+ (therefore we use D+ for the ...

The problem is not only with cdc_acm, but with all host side software. Libusb has different API functions for bulk and interrupt endpoints. Software which is written for one type of endpoint won't accept the other.

And take the difference with what? You need two captures which are a known number of cycles apart. This is easiest done with an interrupt.

Newer versions of PowerSwitch use the delay function (eith a much longer delay, BTW) instead.

If you use the input capture unit, you still get an interrupt every cycle. That gives the maximum frequency of ~ 3 kHz.

Other than that, the input capture unit can be very handy for precise measurements. I had frequency resolutions of more than 22 bits.

Yes, Bulk endpoints are not allowed for low speed devices. There is no particular reason for this (at least not these days with USB 2.0 hubs), but the standard defines it this way. [For USB 1.0 hubs, this was a performance problem since polling blocks the bus for a long time.] Since it's additional ...

You can contact me at the AVR-USB support address.

Can you please be more precise: How many 1N4148 did you use? What was the resulting supply voltage at the AVR? What's the idle voltage on D-?

The 1kHz SE0 pulses are on D-, not D+. You therefore need an interrupt on D-.

Thanks! I've added a link to the project page.

If D- is wired to a pin which can trigger an interrupt (e.g. INT1, pin change interrupt), there's also an example available how to implement it. Suspend mode is documented in the USB specification. When the host goes to sleep it MUST stop sending the 1 kHz pulses. The device may wake up the host by ...

You must reset data toggling after each new connection. Do you lose the first chunk or one in the middle? When you generate a trigger in usbFunctionWriteOut() if data toggling is wrong, you should see many DATA packets which are answered with a NAK between the two with the same token. The main loop ...