First off, some clarifications from discoveries since the last log:

1. The USB B /CH340 and ESP8266 share the same USART, Serial1. This is why plugging in USB kills the ESP - they didn't want conflicts.

2. I've had no success getting USB working through the female connector, despite having a spare A->A cable. The serial that works is the output of the CH340, and it should be zero surprise it works since it's basically a dedicated FTDI clone.

Secondly...never accidentally leave test code in.

I removed a "blink forever" line from Marlin's main, re-enabled watchdog, and boom, I can issue commands to Marlin. After a few more adjustments it will be time to plug it into the printer.

Did I mention you can do WIFI printing? Yeah. You connect to Marlin by telnetting to Port 23 on the ESP and using the Serial bridge. Soon Windows, Com0Com will give you a virtual com port for Marlin. Or ESP3D could be run.

What does not work:

SD. Marlin uses SPI. This board uses SDIO. I need to test if SDIO via Arduino libraries works.

LCD. Nope, not even a little bit, yet. I'll need to figure out FSMC initialization before it will work.

All changes are pushed to my github, so you can enjoy if broken builds of Marlin are your thing.

start
echo: External Reset
Marlin bugfix-2.0.x

echo: Last Updated: 2018-01-20 | Author: (xC0000005, Lerdge-X Config)
echo:Compiled: Dec 29 2018
echo: Free Memory: 51035  PlannerBufferBytes: 1344
echo:Hardcoded Default Settings Loaded
echo:  G21    ; Units in mm (mm)

echo:Filament settings: Disabled
echo:  M200 D3.00
echo:  M200 D0
echo:Steps per unit:
echo:  M92 X80.00 Y80.00 Z4000.00 E500.00
echo:Maximum feedrates (units/s):
echo:  M203 X300.00 Y300.00 Z5.00 E25.00
echo:Maximum Acceleration (units/s2):
echo:  M201 X3000.00 Y3000.00 Z100.00 E10000.00
echo:Acceleration (units/s2): P<print_accel> R<retract_accel> T<travel_accel>
echo:  M204 P3000.00 R3000.00 T3000.00
echo:Advanced: B<min_segment_time_us> S<min_feedrate> T<min_travel_feedrate> X<max_x_jerk> Y<max_y_jerk> Z<max_z_jerk> E<max_e_jerk>
echo:  M205 B20000.00 S0.00 T0.00 X10.00 Y10.00 Z0.30 E5.00
echo:Home offset:
echo:  M206 X0.00 Y0.00 Z0.00
echo:PID settings:
echo:  M301 P22.20 I1.08 D114.00
echo:SD init fail
G1 X
ok
M503
echo:  G21    ; Units in mm (mm)

echo:Filament settings: Disabled
echo:  M200 D3.00
echo:  M200 D0
echo:Steps per unit:
echo:  M92 X80.00 Y80.00 Z4000.00 E500.00