This 2-in-1 PR started with the goal of support the Bangle.js 2
smartwatch with *no USB*.
* Adds "secure" DFU build support with a committed private key.
* Adds 3-bit color support with one dummy bit for the JDI memory display
* Allows nrf boards to have a board_background_task() run in RUN_BACKGROUND_TASK.
This is needed because the Bangle.js 2 uses the watchdog to reset.
* Renamed port_background_task() to port_background_tick() to indicate it
runs on tick, not RUN_BACKGROUND_TASK.
* Marks serial connected when the display terminal is inited. This means
that safe mode messages show up on the display.
ACep, 7-color epaper displays also pack 3 bits in 4. So, I added that
support as well.
* Adds 3-bit ACeP color support for 7-color e-paper displays. (Not
watch related but similar due to color depth.)
* Allows a refresh sequence instead of a single int command. The 7" ACeP
display requires a data byte for refresh.
* Adds optional delay after resetting the display. The ACeP displays
need this. (Probably to load LUTs from flash.)
* Adds a cleaning phase for ACeP displays before the real refresh.
For both:
* Add dither support to Palette.
* Palette no longer converts colors when set. Instead, it caches
converted colors at each index.
* ColorConverter now caches the last converted color. It should make
conversions faster for repeated colors (not dithering.)
Another reduction of -48 bytes can be had if the fine calculation
step is skipped. The worst difference compared to the old reference
code with my calibration values in the 0° to 60° was 2°C,
and the difference at 25°C is 1°C.
The final size decrease for non-full builds like Trinket M0 is 268
bytes.
Perform most arithmetic with scaled integer values.
For my calibration values
```
const uint32_t NVMCTRL_TEMP_LOG[]={0xfc05511e, 0xcc7ac0f7};
```
the maximum difference between the old and new calculation is 0.50°C.
The difference is smallest (0.13°) at 25.87°C in the old scale.
This reduces mcu_processor_get_temperature from 568 bytes to 348 bytes
(-220 bytes)
This tweaks the RMT timing to better match the 1/3 and 2/3 of 800khz
guideline for timing. It also ensures a delay of 300 microseconds
with the line low before reset.
Pin reset is now changed to the IDF default which pulls the pin up
rather than CircuitPython's old behavior of floating the pin.
Fixes#5679
Initially enabled for samd51, this enables reading raw flux data as well
as DOS/MFM formatted media.
This is only the low-level code for reading & decoding flux pulses from a floppy drive.
high level details will live in a Python library.
adafruit-circuitpython-floppy will take care of details like stepping
from track to track, etc.
The port is free to return NULL for any/all of these, and the caller has
to check.
This will be used in the floppy code, because aside from getting the
registers, it looks like all is independent of MCU.
