Paul (or anybody else who has played with the Atmel USB controller):

I'm using PJRC's usb_serial sample code from the AT90USB1286 (?)
Teensy-2 tarballs on my AT90USB82-based 7-segment display.  It compiles
and runs OK, the device enumerates on Linux, and I can send characters
from the PC to the AVR, where I receive them with usb_get_serial (or
something like that).

HOWEVER...for some reason, usb_send_serial (with or without a subsequent
flush) doesn't seem to send characters from the AVR to the PC.

My understanding of USB is that even unidirectional transfer (e.g.
PC->AVR) requires both low-level USB directions to work, so it's not
like my problem is that D- or D+ is disconnected.  However, I don't know
where to look next.  The PC->AVR side works reliably, AFAICT, but the
AVR->PC doesn't work at all.

Any pointers, anybody?

(Incidentally, I use the same PJRC code in a bare-metal program that
runs on a Teensy-2, and both directions work fine.  Is there some
significant difference between the USB controllers on ATmega32U4 and
AT90USB82?  I'll try it on a Teensy++-2.0, with the AT90USB1286.  Maybe
it's just a low-memory issue?)
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