> 64 byte endpoints on XMega

[Nick Sayer]

I see the release notes say >64 byte endpoints aren't supported, and - sure enough - they don't work.

I've started down the road of seeing if I could fix it. I found the most obvious things to change in Endpoint_XMEGA.h - namely the test in Endpoint_ConfigureEndpoint and the size of Data[] in Endpoint_FIFO_t, but that doesn't seem to be enough. It seems like the first large transfer (this is a mass storage device) causes the device to just hang during setup - it never even gets to the point of starting the bulk data movement.

I can't see any other overt references to 64 that would seem to matter, and I don't see anything in the XMega manual that talks about such a limitation.

Can someone point me in the right direction?

[Nick Sayer]

Oh, never mind. I see the problem. Buffers larger than 64 bytes are only supported for isochronous transfers (table 20-5, http://www.atmel.com/Images/Atmel-8331-8-and-16-bit-AVR-Microcontroller-XMEGA-AU_Manual.pdf).

Bummer.

[Paul Stoffregen]

That's not just an AVR Xmega limitation.

The USB spec says the maximum packet size at 12 Mbit/sec full speed is 64 bytes for control, bulk and interrupt endpoints.  Only isochronous is allowed larger packets, up to 1023 bytes.

At 480 Mbit/sec high speed, bulk and interrupt are allowed to use up to 512 bytes.  Control is still limited to 64 bytes.  Isochronous gets a maximum of 1024 bytes, a whopping 1 byte increase!  There's also special support for a high bandwidth mode, when I don't fully understand, that transfers 3 packets with minimal gaps.  I've seen mention of this effectively allowing 3072 byte isochronous.  It's one of many USB features than only exists at 480 Mbit/sec or higher.

At 1.5 Mbit/sec low speed, bulk and isochronous aren't allowed at all, and the others are limited to only 8 bytes.

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