Removed `usbDelay(uint32_t cycles)`, added `usbSleep(uint32_t millis)`
The same method signature could cause silent code breakage at runtime,
as opposed to noisy code breakage at compile time which is the better
kind.
This patch adds calls to usbPoll in the progress callback. This
should address #98.
We call usbDelay instead of Poll, to call usbd_poll several times.
Otherwise it would only handle one event instead of handling all
events that were pending so far. The ugly magic number 5 is a guess.
Note that we also need to set usbTiny, so that we don't recursively
process messages. Since we don't know whether usbTiny is set, we
need to store the old value (especially true for u2f).
This fix also relies on another fix in libopencm3.
Clear storage marker first before clearing the second sector to prevent
leaving a state where only PIN failures have been cleared but storage is
still present.
Instead of reflashing the whole storage, we use a designated area
in the second storage block, where we mark each PIN failure by a
single zero bit. This is because one can set bits in flash to zero but
not to one. If the PIN was entered successfully the whole word is
set to zero and the next word stores the new PIN failure counter.
This diff contains three changes.
1. Make timing isPinCorrect independent of storage.pin, to avoid timing attacks
2. Only update failed PIN counter if the user entered a PIN.
Of course, the fail counter is still incremented, before the PIN is checked.
3. Don't cache the PIN, but just the fact that the PIN was entered. The
cache should be in sync with storage.pin in any case.
