Recore A4

Recore Rev A4

Recore is a 3D-printer control board running Linux. It is specifically tailored to be compatible with Klipper and OctoPrint. The main features are:

• Allwinner A64 SoC, quad core CPU running at 1 GHz.
• 1 GB or DDR3 RAM
• 8 GB of on board eMMC
• Gigabit Ethernet
• 6 TMC2209, 2 A stepper motor drivers
• 3 heater outputs + high power heated bed
• 4 USB High Speed ports
• 4 thermistor/thermocouple inputs (software selectable)
• Comes with Debian Linux with Klipper and OctoPrint installed

This document is for Recore Revision A4. For previous hardware revisions, please see:

• Recore_A3
• Recore_A2

Hardware overview

Pinout

A64

I the following table the pins used for End-stops and stepper control are described. The "bank and pin" can be used to specify the pin numbers in klipper. The "Number" column is useful for testing things on the command line in conjunction with gpiod.

Pinout
Name	Bank and pin	Number
END STOP 0	PH4	228
END STOP 1	PH5	229
END STOP 2	PH6	230
END STOP 3	PH7	231
END STOP 4	PH8	232
END STOP 5	PH9	233
STEP 0	PL4	4
STEP 1	PL5	5
STEP 2	PL6	6
STEP 3	PL7	7
STEP 4	PL8	8
STEP 5	PL9	9
STEP 6	PL10	10
STEP 7	PL11	11
DIR 0	PE8	136
DIR 1	PE9	137
DIR 2	PE10	138
DIR 3	PE11	139
DIR 4	PE12	140
DIR 5	PE13	141
DIR 6	PE14	142
DIR 7	PE15	143
STEP DIAG 0	PE0	128
STEP DIAG 1	PE1	129
STEP DIAG 2	PE2	130
STEP DIAG 3	PE3	131
STEP DIAG 4	PE4	132
STEP DIAG 5	PE5	133
STEP DIAG 6	PE6	134
STEP DIAG 7	PE7	135
OC-ALERT	PG0	192
OC-RESET	PG1	193
EN-HP	PG2	194
UC-INT-1	PG3	195
UC-NRST	PG4	196
UC-BOOT	PG5	197
ES-EN-12V	PG8	200
EN-HDMI-PWR	PG9	201
EN-THERMISTORS	PG10	202
EN-ENDSTOPS	PG11	203
USB-PWR-EN-0	PH0	224
USB-PWR-EN-1	PH1	225
USB-PWR-EN-2	PH2	226
USB-PWR-EN-3	PH3	227
GAIN-ENABLE-T0	PD4	100
GAIN-ENABLE-T1	PH11	235
GAIN ENABLE T2	PE17	160
PU-ENABLE-T0	PD6	102
PU-ENABLE-T1	PD24	120
PU ENABLE T2	PF0	160
PU ENABLE T3	PF1	161
STEPPER UART_RX 0-3	PB1
STEPPER UART_TX 0-3	PB0
STEPPER UART RX 4-5	PD1
STEPPER UART TX 4-5	PD0
STEPPER UART 6	PD2	98
STEPPER UART 7	PD3	99

STM32F030

Pinout
Name	Bank and pin	Number
THERMISTOR 0	PA0	6
THERMISTOR 1	PA1	7
THERMISTOR 2	PA2	8
THERMISTOR 3	PA3	9
BOARD VOLTAGE	PA4	10
BOARD CURRENT	PA5	11
BOARD TEMPERATURE	PA6	12
COLD JUNCTION	PA7	13
FAN 0	PB0	14
FAN 1	PB1	15
FAN 2	PB5	28
FAN 3	PB4	27
HEATER E0	PA8	18
HEATER E1	PA9	19
HEATER E2	PA10	20
HEATER BED	PA11	21
USER LED	PA12	22
EXT 1	PA8	32
EXT 2	PB7	30

Inductive Sensor

Connect the inductive sensor on ES0. You can choose either 5V or 12V output on the voltage pin.

Pinout
Name	Number
Black	signal
Blue	GND
Brown	12V

Connectors

Four pin male: TBP01P1-508-04BE

Two pin male: TBP01P1-508-02BE

Software for Recore

Recore should come pre-flashed with ReFactor image. If you want to update that, here are the steps:

1. Flash the ReFactor Linux distro to a USB drive.
2. Insert the Recore board in a host computer with the USB-C connector.
3. If the eMMC is blank or the "FEL" button is pressed, the board will go into bootloader mode.
4. Upload SPL, EL3 and u-boot through the USB port.
5. The board will boot using the USB drive.
6. Copy the contents of the USB drive into the eMMC/Internal flash.

ReFactor

Flashing ReFactor from a USB drive

Get the latest ReFactor image from here: https://github.com/goeland86/ReFactor/releases for example:

wget https://github.com/goeland86/ReFactor/releases/download/v3.0.0-RC4/ReFactor-recore-v3.0.0-RC4.img.xz

Assuming you have managed to boot Recore from a USB flash drive and you have the ReFactor image available in the same folder, you can use dd to do a direct transfer of the image from the USB drive to eMMC.

xz -v -d -c Refactor-recore-v3.0.0-RC3.img.xz  | dd of=/dev/mmcblk0

Booting from USB if an OS is present on the eMMC

If the eMMC is parititioned and has an OS, u-boot will launch right into that. In order to override that and load the boot script from a USB dongle, stop u-boot by pressing a key and then write:

run bootcmd_usb0

In order to mount the root filesystem on the USB stick, you must change the kernel command line. In the file /boot/armbianEnv.txt add the line:

extraargs=root=/dev/sda1

This can be done on the USB stick.

USB initilization takes several seconds, so it has been disabled by default on the later u-boot in Refactor. If USB is not initialized, you can do it manually from u-boot:

usb reset

Install Klipper

With ReFactor, klipper comes pre-installed. However some quirks needs to be done in order to get it working.

cd /home/debian
mv klippy-env klippy-env-py3
virtualenv -p /usr/bin/python2 klippy-env
source klippy-env/bin/activate
pip --upgrade
pip install pyserial greenlet cffi jinja2
deactivate

After the quirks, restart klipper:

systemctl restart klipper

You can check the log by writing

tail -f /tmp/klippy.log 

Install STM32 firmware

This flash scripts requires gpiod

sudo apt install gpiod

cd /home/klipper/klipper
cp .config_stm32 .config
make
gpioset 1 197=1; gpioset 1 196=0; make serialflash FLASH_DEVICE="/dev/ttyS4 -i -196,196"; gpioset 1 197=0

Install AR100 firmware

The AR100 needs a cross compilation toolchain. It can be downloaded from feeds.iagent.no:

cd /opt
wget http://feeds.iagent.no/toolchains/or1k-linux-musl.tar.xz
tar xf or1k-linux-musl.tar.xz
export PATH=$PATH:/opt/output/bin

cd /home/debian/klipper/
cp .config_ar100 .config
make

Running Klipper

After a reboot, the ar100 firmware needs to be reflashed. We will get this into an automatic routine eventually, bit for now:

sudo /home/klipper/klipper/scripts/flash-ar100.py /home/klipper/klipper/out/ar100.bin

While details are ironed out there is a script that can be used to restart Klipper that will handle resetting things and setting up the steppers etc.

/home/klipper/klipper/scripts/restart-recore.py

Giving right privileges for AR100 restart

The AR100 flasher and reset script needs to be run as root. We create a group called flashers, add klipper to that and gie the group sudo access to the script

sudo addgroup flashers
sudo adduser klipper flashers
echo '%flashers ALL=(ALL) NOPASSWD: /home/klipper/klipper/scripts/flash-ar100.py *, /usr/bin/gpioset *' > /etc/sudoers.d/flashers

Install Octoprint

su klipper
cd ~
sudo apt update
sudo apt install python-pip python-dev python-setuptools python-virtualenv git libyaml-dev build-essential
mkdir OctoPrint && cd OctoPrint
virtualenv venv
source venv/bin/activate
pip install pip --upgrade
pip install octoprint
./venv/bin/octoprint serve

Add a systemd start-up script

nano /lib/systemd/system/octoprint.service

Add the following content

[Unit]
Description=The snappy web interface for your 3D printer
After=network-online.target
Wants=network-online.target

[Service]
Type=simple
User=klipper
ExecStart=/home/klipper/OctoPrint/venv/bin/octoprint

[Install]
WantedBy=multi-user.target

Enable and start script

sudo systemctl enable octoprint
sudo systemctl start octoprint

Software for Recore

Recore should come pre-flashed with ReFactor image. If you want to update that, here are the steps:

1. Flash the ReFactor Linux distro to a USB drive.
2. Insert the Recore board in a host computer with the USB-C connector.
3. If the eMMC is blank or the "FEL" button is pressed, the board will go into bootloader mode.
4. Upload SPL, EL3 and u-boot through the USB port.
5. The board will boot using the USB drive.
6. Copy the contents of the USB drive into the eMMC/Internal flash.

ReFactor

Flashing ReFactor from a USB drive

Get the latest ReFactor image from here: https://github.com/goeland86/ReFactor/releases for example:

wget https://github.com/goeland86/ReFactor/releases/download/v3.0.0-RC4/ReFactor-recore-v3.0.0-RC4.img.xz

Assuming you have managed to boot Recore from a USB flash drive and you have the ReFactor image available in the same folder, you can use dd to do a direct transfer of the image from the USB drive to eMMC.

xz -v -d -c Refactor-recore-v3.0.0-RC3.img.xz  | dd of=/dev/mmcblk0

Booting from USB if an OS is present on the eMMC

If the eMMC is parititioned and has an OS, u-boot will launch right into that. In order to override that and boot from a USB dongle, stop u-boot by pressing a key and then write:

setenv devnum 0
run usb_boot

Install Klipper

With ReFactor, klipper comes pre-installed. However some quirks needs to be done in order to get it working.

cd /home/debian
mv klippy-env klippy-env-py3
virtualenv -p /usr/bin/python2 klippy-env
source klippy-env/bin/activate
pip --upgrade
pip install pyserial greenlet cffi jinja2
deactivate

After the quirks, restart klipper:

systemctl restart klipper

You can check the log by writing

tail -f /tmp/klippy.log 

Install STM32 firmware

This flash scripts requires gpiod

sudo apt install gpiod

cd /home/klipper/klipper
cp .config_stm32 .config
make
sudo ./scripts/flash-stm32.sh out/klipper.bin (might have to be run several times)

Install AR100 firmware

The ar100 needs to be compiled on an x86_64 computer. The reason for this is the lack of an or1k toolchain for aarch64. On a host computer:

cp .config_ar100 .config
make
scp out/ar100.bin root@recore.local:/home/klipper/klipper/out/

On the Recore board:

sudo /home/klipper/klipper/scripts/flash-ar100.py /home/klipper/klipper/out/ar100.bin

Running Klipper

After a reboot, the ar100 firmware needs to be reflashed. We will get this into an automatic routine eventually, bit for now:

sudo /home/klipper/klipper/scripts/flash-ar100.py /home/klipper/klipper/out/ar100.bin

While details are ironed out there is a script that can be used to restart Klipper that will handle resetting things and setting up the steppers etc.

/home/klipper/klipper/scripts/restart-recore.py

Giving right privileges for AR100 restart

The AR100 flasher and reset script needs to be run as root. We create a group called flashers, add klipper to that and gie the group sudo access to the script

sudo addgroup flashers
sudo adduser klipper flashers
echo '%flashers ALL=(ALL) NOPASSWD: /home/klipper/klipper/scripts/flash-ar100.py *, /usr/bin/gpioset *' > /etc/sudoers.d/flashers

Install Octoprint

su klipper
cd ~
sudo apt update
sudo apt install python-pip python-dev python-setuptools python-virtualenv git libyaml-dev build-essential
mkdir OctoPrint && cd OctoPrint
virtualenv venv
source venv/bin/activate
pip install pip --upgrade
pip install octoprint
./venv/bin/octoprint serve

Add a systemd start-up script

nano /lib/systemd/system/octoprint.service

Add the following content

[Unit]
Description=The snappy web interface for your 3D printer
After=network-online.target
Wants=network-online.target

[Service]
Type=simple
User=klipper
ExecStart=/home/klipper/OctoPrint/venv/bin/octoprint

[Install]
WantedBy=multi-user.target

Enable and start script

sudo systemctl enable octoprint
sudo systemctl start octoprint

Manual control and testing

To use the examples in this section, first install gpiod

apt install gpiod

Power domains

There are 9 power domains around the board controlling voltage on different pins:

• Input power controls power to 4 high power outputs, the 4 fans and the 6 stepper drivers. This input has current monitoring, fast acting over current protection, voltage monitoring, temperature monitoring and reverse polarity protection.
• Thermo couple power Controls +5V/1A output to the ADCs. This can be used for turning on power to the analog pins.
• End stop power Controls +5V/1A output on the six endstops. Ganged. ES5 can be switched to have 12V output. The 12V output has a

100mA internal current limit.

• 4 USB host power domains Controls 5V/1A current output to the usb host connectors. These are turned on by u-boot.
• HDMI 5V output Controls the 5V/1A HDMI output. Turned on by u-boot.

Input stage

Reset over current protection and set it in "one-shot" mode.

gpioset 1 193=0
gpioset 1 193=1

The over current protection can also be set in "transparent" mode, where the current alarm will be reset automatically. Note that this is a bad idea for general operation, only use for testing.

gpioset 1 193=0

Enable 24V input

gpioset 1 194=0

End stop 5V /12V

End stop 0 to 4 has a programmable +5V output voltage. End stop 5 has +5V or +12V selectable.

To enable +5V on ES 0...4

gpioset 1 203=1

To disable again

gpioset 1 203=0

To switch to 12V output on ES5

gpioset 1 199=1

To disable again

gpioset 1 199=0

End stops values

To see what value the end stops have

gpioget 1 228 # ES 5
gpioget 1 229
gpioget 1 230
gpioget 1 231
gpioget 1 232
gpioget 1 233 # ES 0

HDMI power

echo 201 > /sys/class/gpio/export
echo out > /sys/class/gpio/gpio201/direction
echo 1 > /sys/class/gpio/gpio201/value

TMC2209

In window/shell 1:

stty -F /dev/ttyS2 raw -echoe -echo
xxd -c 4 /dev/ttyS2

In window/shell 2:

echo -n -e '\x5\x0\x6\x6F' > /dev/ttyS2

The return should be along the lines of

00000000: 0500 066f  ...o
00000004: 05ff 0620  ... 
00000008: 0001 4058  ..@X

To read the OTP registers

echo -n -e "\x5\x0\x5\x21" > /dev/ttyS2
echo -n -e "\x5\x0\x5\x21" > /dev/ttyS3
echo -n -e "\x5\x1\x5\x97" > /dev/ttyS2
echo -n -e "\x5\x1\x5\x97" > /dev/ttyS3
echo -n -e "\x5\x2\x5\x7a" > /dev/ttyS2
echo -n -e "\x5\x2\x5\x7a" > /dev/ttyS3
echo -n -e "\x5\x3\x5\xcc" > /dev/ttyS2
echo -n -e "\x5\x3\x5\xcc" > /dev/ttyS3

To set the OTP register to use RDSon:

echo -n -e "\x5\x0\x84\x0\x0\xbd\x6\xac" > /dev/ttyS2

To check that no errors are reported by the steppers write this on the command line. If a "1" shows up, that is an indication that the motor is reporting an error.

gpioget 1 128
gpioget 1 129
gpioget 1 130
gpioget 1 131
gpioget 1 132
gpioget 1 133

STM32F031

There is a small firmware to test all functionality that is controlled by the STM32F031 chip on the board. Once uploaded to the board using the flash script, the firmware will turn on all LEDs it controls and send back ADC readings.

To flash this firmware to the STM32:

gpioset 1 197=1
gpioset 1 196=0
stm32flash -i -196,196 -w Sumato-f031.bin -v -g 0x00 /dev/ttyS1
gpioset 1 197=0
stm32flash -i -196,196 /dev/ttyS1

To see the ADC readings:

stty -F /dev/ttyS3 38400 raw
cat /dev/ttyS3

You should see something like

ADC T0: 0
ADC T1: 0
ADC T2: 0
ADC T3: 0
ADC U: 2338
ADC I: 0
ADC TB: 3417

The following one-liners assumes gawk is installed.

Reading Current

The current shunt resistor is 1 mOhm, the amplifier is 20 times, the vref is 3.3V, so we get: (adc_val/4096*3.3)*1000/20 = (adc_val/4096)*165 You can convert the current (as in amps) reading to something useful like this:

cat /dev/ttyS4 | awk '/I:/ { printf "scale=4; (%i/4096)*165\n", $3; fflush(); }' | bc -l

Reading Board Temperature

To see the temperature readings, try this :

export beta=4327
cat /dev/ttyS1 | awk '/TB:/ { printf "scale=4; 4327/l( (4700/((3.3/(3.3*%i/4096))-1.0))/0.05306820342563400000) -273.15\n", $3; fflush(); }' | bc -l | awk '{print strftime("%k:%M:%S"), $0; fflush();}'

Reading Input Voltage

To see voltage on the input, it can be converted like this:

exec 4</dev/ttyS4 5>/dev/ttyS4
echo -n ";A4;" >&5
read -t1 reply <&4
echo $reply | awk '{ printf "scale=4; (%i/4096)*3.3*((100+10)/10)\n", $4; fflush(); }' | bc -l

Thermistor inputs

To enable pull-up on input for using thermistors for temperature measurements:

gpioset 1 102=1
gpioset 1 120=1
gpioset 1 160=1
gpioset 1 161=1

Setting Op-amp gain to 1:

gpioget 1 100
gpioget 1 235
gpioget 1 145
gpioget 1 34

In the device tree file, the gpio/ldos must be set to gpio input:

&gpio0_ldo {
  function = "gpio_in";
};

Thermocouple input

Either a thermocouple or a thermistor can be used as input on the T0-T3 inputs.

Bias

The thermocouple is set up to have a Bias of 0.7V/100 on the input which enables negative values (lower than the board temperature) as input to the ADCs. With the input short circuited, the bias can be recorded. Typical values are 750 This needs to be subtracted from the result.

Cold junction compensation

Another important aspect is cold junction compensation. There is a thermistor connected on the board close to the thermocouple inputs which can be used to measure the temperature close to the input junction. This temperature must be added in software.

For Rev A3, the cold junction compensation is actually located a bit away from the junction, so it might not be accurate. The connected thermistor is a TDK NTCG104EF104FT1X The connected Thermocouple has a (25/100) beta value of 4327. Beta 25/85 used in Klipper is 4308K

In order to use the inputs for thermocouple, the pull-up resistors must be deactivated:

gpioget 1 102
gpioget 1 120
gpioget 1 160
gpioget 1 161

Also, the op-amp needs a gain of 100:

gpioset 1 100=0
gpioset 1 235=0
gpioset 1 145=0
gpioset 1 34=0

Finally, the input bias needs to be enabled. The following LDOs needs to be enabled:

reg_ldo_io0
reg_ldo_io1
reg_dldo3
reg_dldo4

AR100

Please see: AR100

Performance

Start-up time

With a maximum clock for MMC2 of 200 MHz, here is the start-up time:

root@recore-3:~# systemd-analyze 
Startup finished in 5.128s (kernel) + 11.567s (userspace) = 16.695s 
graphical.target reached after 11.421s in userspace

Measured voltages

Instruments used:

• Siglent SDM3065X, 6.5 digit multimeter
• HP 3458A, 8.5 digit multimeter
• HP 3245A, Universal Source

Microcontroller voltages

VDDA uC: 3.312 V
VDD uC: 3.312 V

Voltage from the PMIC supplied as bias:
0.706 V

Offset and Gain Measurements

Input voltage measured with SDM3065X, output voltage measured with 3458A. Programmable Voltage reference used was the DIY DAC cape made by Elias. Measurements should be repeated with HP 3245A.

Op-amp gain measurements
Vin (mV)	Vout (V)	Gain
1.0103	0.754	95.73
2.0038	0.8492	95.78
3.013	0.9457	95.72
4.0032	1.04	95.60
5.0108	1.1372	95.78
6.0016	1.232	95.76
7.0094	1.3285	95.76
8.0015	1.4235	95.76
9.0106	1.5201	95.76
10.0005	1.615	95.77
11.0102	1.7116	95.76
12.0042	1.8067	95.75
13.0142	1.9035	95.76
14.0056	1.9985	95.76
15.0145	2.095	95.76
16.0055	2.1899	95.76
17.0145	2.2865	95.75
18.0055	2.3813	95.75
19.0163	2.4783	95.76
20.0067	2.5723	95.72

An experiment was done using an HP 3245A and a HP 3458A measuring the input and output voltages and calculating offset and gain. This will become a part of a calibration routine during final testing and flashing, values should be stored with the board.

Input 1	Vin	Vout	Offset	
	0.0003	0.6685	0.6685	
				
Vin set	Vin	Vout	Gain	Deviation
-5 mV	-4.9983	0.1840	96.93	0.16
0 mV	0.0003	0.6685	96.76	-0.01
5 mV	5.0000	1.1523	96.77	0.00
10 mV	10.0013	1.6355	96.69	-0.08
15 mV	15.0005	2.1198	96.75	-0.01
20 mV	20.0005	2.6025	96.70	-0.07
	Average gain		96.77	
				
				
				
Input 2	Vin	Vout	Offset	
	0.0017	0.6485	0.6483	
				
				
Vin set	Vin	Vout	Gain	Deviation
-5 mV	-4.9961	0.1722	95.30	-0.07
0 mV	0.0017	0.6485	95.37	-0.01
5 mV	5.0014	1.1253	95.37	-0.01
10 mV	10.003	1.6025	95.39	0.01
15 mV	15.0021	2.0793	95.38	0.01
20 mV	20.0023	2.5559	95.37	-0.01
	Average gain		95.38	
				
				
Input 3	Vin	Vout	Offset	
	0.0013	0.6560	0.6559	
				
				
Vin set	Vin	Vout	Gain	Deviation
-5 mV	-4.9969	0.1794	95.35	-0.02
0 mV	0.0013	0.6560	95.35	-0.03
5 mV	5.0012	1.1329	95.38	0.01
10 mV	10.0025	1.6098	95.37	-0.01
15 mV	15.0015	2.0864	95.36	-0.02
20 mV	20.0013	2.5631	95.35	-0.02
	Average gain		95.36	
				
				
Input 4	Vin	Vout	Offset	
	0.0024	0.6498	0.6496	
				
				
Vin set	Vin	Vout	Gain	Deviation
-5 mV	-4.9954	0.1714	96.98	1.18
0 mV	0.0024	0.6498	94.50	-1.31
5 mV	5.0015	1.1283	95.96	0.16
10 mV	10.0028	1.6069	95.83	0.02
15 mV	15.0024	2.0853	95.78	-0.02
20 mV	20.0022	2.5642	95.78	-0.02
	Average gain		95.81	

5V Buck converter ripple and noise

The 5V step down/Buck converter is a AOZ2151PQI-10. It can provide 4A and has an input voltage range of 12-28V. It is hard wired to be in PWM mode. PFM mode results in a loud whine.

Below is a screenshot of the ripple and noise across the the 5V rail with a normal kernel running.

Input stage

An experiment with a constant current load drawing 20 A from the bed connector with and without a 92 mm fan on top of the board for forced convection. The temperature measured was with the on board thermistor. Using a thermal camera, the temperature displayed matches well with the temperature reported by the camera. However, in Rev A2, this is not the hottest point on the board. The MOSFET controlling the bed seems to consistently get the highest temperature. The reason for this is probably due to a 3.3 V VGS.

Inrush current

During turn on of the high power stage, there will be an inrush current to charge up the bank of capacitors present on the board. If no loads are turned on, the inrush current reaches 31 A at peak. This is important to consider when setting the current limit with device tree.

Temperature low pass filter

A Low pass filter has been added on each of the temperature input channels. The cut-off frequency is below what my oscilloscope can handle, but a plot in the time domain verifies a 7 Hz -3dB point.

ADC offset and gain measurements

To measure the ADC offset error, measure the voltage on the uC input pin and record when the transition from 0 to 1 occurs. It should occur at 0.5 LSB = 3.3/4096/2 = 0.4028 mV. Offset: 55.35 mV - 0.4028 mV = 54.95 mV

FAQ

A: It's only the board, no connectors at all.

There will be a bag of connectors available to purchase eventually, but for now you will have to supply your own.

A: There are 6 pins available from the main SoC that can be used for various things.

There is no hardware SPI, but you can make a program that uses soft SPI. There is no dedicated I2C, but perhaps that would be a nice addition.

Known Issues

Too low capacitance on USB nodes

High current draw on USB lines can cause instability in some devices. Specifically having a webcam or a wifi dongle and a Manga Screen 2 can cause flicker on the screen.

Manga Screen EDID not always read correctly

There seems to be a timing issue with powering the display and reading the EDID. The EDID is not always read correctly during boot.

Ethernet adapter not reset correctly

Often times the ethernet chip is not reset correctly. The symptoms are that no IP address is given to the board. A possible workaround is a manual reset of the eth chip:

gpioset 1 110=0
sleep 1
gpioget 1 110

Reboot possibly not working when power by USB

It seems that powering the board by USB might cause reboot to have problems. Needs verification.