This is an initial cut for feedback.
Chamber temperature is currently reported along with hot end and bed
temperatures to serial. The format is just like that used for hot end
and bed temperatures, but using 'C' prefix. As there is no heater,
target is always 0. Is this appropriate, is there a better way to report
chamber temperatures?
Chamber temperatures are not reported on the LCD in any way.
When auto chamber fan is enabled, it currently just uses the same
temperature threshold as the other auto controlled fans.
As the chamber temperature is not connected to any heater, it doesn't
undergo mintemp/maxtemp monitoring. This would need to change in the
future if chamber heating became a feature.
Reverse engineered from the unpublished firmware from Creality,
inferring the base version and configuration they used. The basis is
the firmware version from "Jul 31 2017 10:16:30". Configurations were
found by seeing what code was compiled into the firmware, and
constants used there.
They used Marlin 1.0.1, because
* 1.0.0 had very different serial output in `setup()` and overall
code structure.
* 1.0.2 changed the `VERSION_STRING` to include a leading space,
and `lcd_init` uses `SET_INPUT` instead of `pinMode`.
For U8Glib, a version between 1.14 and 1.17 was used, because
* 1.12 didn't have the extra speed argument to u8g_InitCom.
* 1.13 didn't have the soft reset instruction for UC1701 initialization.
* 1.18 has a new directory structure.
Quirks
* The value of PID_dT hints that F_CPU is 20M, but MarlinSerial.begin
suggests it's indeed 16M (and the board uses 16M). Left at 16M for now.
* The LED and DOGLCD_CS are on the same pin.
Implements changes to LCD and encoder pins from
forums.reprap.org/read.php?110,716538,728278 and also sets
ST7920_DELAY_[1-3] to DELAY_2_NOP to be compatible with the slower LCD
