this loops an image from the camera to the oled display in real time.
it will also dump the Y (luminance) data to to a serial port for
offline development & testing of the QR code algorithm.
- fix tx_await() condition to consider both control and tx channels
- make tx_async more efficient for the common case that the buffer
fits in a single transaction by appending the CS de-assert as part
of the initial command stream
- make trait for the udma global clock setting
The high bit in this exploration is that there seems to be no
way to actually confirm when a UDMA transaction has fully completed
on the hardware interface. All the completion signals tell you
when the software-side UDMA resources are freed up. However, in this
case, the hardware-side resources may still be transmitting/receiving
data.
This is a problem for the case of a '4-wire SPI' display where you
need to set an extra line to control command/data mode addressing.
In this case, the current work-around is to read back the state of
the chip select pin as a GPIO to determine when the hardware has
finished.
I suspect that if we can figure out how to use UDMA in a full duplex
mode that we could do something more essentially linked to the
hardware, but this would also require having a dummy Rx buffer allocated
that is the same depth as the hardware Tx buffer if all you cared about
is the hardware conclusion of a Tx.
Realized that the last round of mixed values wasn't actually being
used because we nuke the `seed` value at the top of the loop.
We effectively had a round of ChaCha8 that we were doing but then
throwing away.
This construction should capture all the benefit of the computation
without wasting computation.
- use proper seeding of entire state
- chacha8 does not evolve internal state when extracting the seed,
so we have to run the cipher some to force mixing of the seed
state.
