Recore A8

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 of 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, MainSail or Fluidd installed

This document is for Recore Revision A8. For previous hardware revisions, please see:

• Recore_A7
• Recore_A6
• Recore_A5
• Recore_A4
• Recore_A3
• Recore_A2

Availability

Recore A7 can be purchased from the Intelligent Agent web shop https://www.iagent.no/product/recore/

Schematics

Recore is "open schematic", it is available here: https://github.com/intelligent-agent/Recore/blob/master/Schematics/Recore_A7.pdf

3D model

A STEP file of the PCB with components is available here: https://github.com/intelligent-agent/Recore/blob/master/3D-files/Recore_A7.step

Pinout

A64

The Allwinner A64 is a quad core Cortex A53 clocked at 1 GHz. It has an integrated RISC CPU (AR100) clocked at 300 MHz that handles the real time aspect for the 3D-printer. In 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.

Name	Bank and pin	Number	Name	Bank and pin	Number	Name	Bank and pin	Number
STEP 0	PL4	4	END STOP 0	PH4	228	OC-ALERT	PF6	166
STEP 1	PL5	5	END STOP 1	PH5	229	OC-RESET	PF4	164
STEP 2	PL6	6	END STOP 2	PH6	230	EN-HP	PF5	165
STEP 3	PL7	7	END STOP 3	PH7	231	UC-INT-1	PG3	195
STEP 4	PL8	8	END STOP 4	PH8	232	UC-NRST	PG4	196
STEP 5	PL9	9	END STOP 5	PH9	233	UC-BOOT	PG5	197
STEP 6	PL10	10	GAIN-ENABLE-T0	PD4	100	ES-EN-12V	PF0	160
STEP 7	PL11	11	GAIN-ENABLE-T1	PH11	235	EN-THERMISTORS	PF1	161
DIR 0	PE8	136	GAIN ENABLE T2	PE17	145	EN-ENDSTOPS	PF2	162
DIR 1	PE9	137	GAIN ENABLE T3	PB2	34
DIR 2	PE10	138	PU-ENABLE-T0	PG10	202
DIR 3	PE11	139	PU-ENABLE-T1	PG11	203
DIR 4	PE12	140	PU ENABLE T2	PG12	204
DIR 5	PE13	141	PU ENABLE T3	PG13	205
DIR 6	PE14	142	OFFSET-T0	PG0	192
DIR 7	PE15	143	OFFSET-T1	PG1	193
STEP DIAG 0	PE0	128	OFFSET-T2	PG3	194
STEP DIAG 1	PE1	129	OFFSET-T3	PG8	200
STEP DIAG 2	PE2	130	STEPPER UART 0-3	PE16	144
STEP DIAG 3	PE3	131	STEPPER UART 4-5	PD24	120
STEP DIAG 4	PE4	132	STEPPER UART 6	PD2	98
STEP DIAG 5	PE5	133	STEPPER UART 7	PD3	99
STEP DIAG 6	PD0	96
STEP DIAG 7	PD1	97

STM32F031

The STM32 is a Cortex M0 powered micro controller handling analog inputs and PWM outputs. It does not control any hard real time aspects of the print, that is handled by the AR100 core realized as a separate core in the A64 SoC.

Name	Bank and pin	Number	Name	Bank and pin	Number	Name	Bank and pin	Number
HEATER E0	PA8	18	THERMISTOR 0	PA0	6	ES1-PWM-OUT	PB3	26
HEATER E1	PA9	19	THERMISTOR 1	PA1	7	PWM-ES2-OUT	PB6	29
HEATER E2	PA10	20	THERMISTOR 2	PA2	8	EXT 1	PB7	30
HEATER BED	PA11	21	THERMISTOR 3	PA3	9	EXT 2	PB8	32
FAN 0	PF0	2	BOARD VOLTAGE	PA4	10	EXT 3	PA13	23
FAN 1	PB1	15	BOARD CURRENT	PA5	11	EXT 4	PB2	16
FAN 3	PB4	27	BOARD TEMPERATURE	PA6	12	USER LED	PA12	22
FAN 2	PB5	28	COLD JUNCTION	PA7	13	FAN_CURRENT	PB0	14

DBG header

The debug header has UART 0 layed out on some of the pins and is used for interacting with u-boot and getting early debug messages from the Linux kernel. It also has a the option to connect a "boot" button so the board can be safely started and shut down from the 3D-printers front panel. The USR pin can be used to light up a an LED or some other custom function.

Pin	Function
1	UART RX
2	UART TX
3	3.3V
4	GND
5	BOOT
6	USR

MCU header

The MCU header is used for connecting external peripherals to the STM32F031 micro controller on the board. There are 4 pins in total available to use. In addition, there is a ground pin and a 3.3 V pin available.

Pin	Function	Alt
1	PB7	I2C1_SDA
2	PB8	I2C1_SCL
3	3.3V	0.7-3.3V
4	GND
5	PA13	EXTI 13
6	PB2	EXTI 2

SPI on S6 and S7 headers

Pin	Function	Alt
S6-3	PD0	SPI1_CS
S6-5	PD1	SPI1_CLK
S7-3	PD2	SPI1_MOSI
S7-5	PD3	SPI1_MISO

LEDs

There are 15 white LEDs on the board. Here is what they mean

Name	Location	Meaning
D2	By PMIC	Board powered
D3	By heater BED	BED output on
D4	By fan 0	Fan 0 is on
D5	By fan 1	Fan 1 is on
D6	By heater H2	Heater H2 is on
D7	By fan 2	Fan 2 is on
D8	By heater H0	Heater H0 is on
D9	By fan 3	Fan 3 is on
D10	By heater H1	Heater H1 is on
D12	By input connector	High voltage domain is on
D15	By eMMC chip	eMMC activity
D17	By USB hub chip	USB activitiy
D18	By the USB C connector	Linux Heartbeat
D19	By the A64 SoC	CPU activity
D20	By the STM32	Klipper running on STM32

Buttons

There are 3 push buttons on the board.

Name	Meaning
FEL	Enter FEL-mode of the A64
BOOT	Boots or shuts down the board
RESET	Hard reset of the CPU

Current limits

Note

The amount of current that can be drawn on the two USB host connectors closest to the HDMI connector is not according to spec. The combined current draw for USB 1 and 2 should not exceed 0.4 A.

Name	Limit
5V-ES (endstops)	0.75 A
USB host 3 and 4 each (5VP)	1.1 A
USB host 1 and 2 each (VSP)	0.75 A
Thermistors	0.75 A
MCU connector	0.5 A
Fan connectors	programmable
Heater connectors	programmable

Wiring

Below is a wiring diagram meant to aid in connecting motors, fans, extruders and hot ends to the control board. On the board, there is a small + sign next to output connectors where polarity is important. If passive heating elements are used, polarity is not important, but if those outputs are to be used with SSRs or relays, polarity must be observed.

Network connection

Recore is designed to be controlled through a browser on a computer, so the board must be connected to the local LAN or wifi network. Connect an ethernet cable between the board and a switch. The ping utility can be used to ensure that the board is discovered on the network.

LAN setup

Recore with Refactor is running avahi and should announce itself on the network once a connection has been established. On a Linux based host computer, it is possible to search for a booted device using the following command:

ping recore.local

If the device is present, an SSH connection can be established:

ssh root@recore.local

Furthermore, a web interface running OctoPrint can be found using a browser:

http://recore.local

Wifi setup

Wifi can be set up by connecting a wifi dongle to one of the USB host ports. Once the uSB dongle has been connected, and the board has been booted, access to the terminal command line can be given through a host computer. The board should appear as a TTY ACM device. On a Linux based host computer, the terminal program `screen` can be used to get access. From the host computer

screen /dev/ttyACM0 115200

If the host computer is running Windows, Putty can be used to get access.

Once a connection has been established, the wifi network can be set up using the command nmtui.

nmtui

Follow the instructions on screen to edit and activate the wifi connection.

Note

If the board is powered through the USB C connector, only the two USB host ports next to the HDMI port is powered.

Mating Connectors

The power connectors on the board are available either in the web shop as part of a connector pack or directly from Digi-key etc.

Four pin male: TBP01P1-508-04BE [| Digi-key]

Two pin male: TBP01P1-508-02BE [| Digi-key]

Klipper Configuration

There are no jumpers on Recore and no hard fuses. Everything is software configurable and resettable from software. This gives great power and flexibility without requiring physical access to the board once it has been installed. But with great power comes great responsibility. It is possible to break things if care is not taken during setup. There is one setting in particular that is worth mentioning: ES0 can have either +5V or +12V on the power pin. This is in order to allow a standard industrial inductive sensor to be used on that end stop. If a 5V only peripheral is connected, that could damage the connected peripheral.

The default config file for Recore A6 can be found in the repository: generic-recore-a7.cfg

TMC2209

The 6 stepper drivers on Recore are of type TMC2209 from Trinamic. Each stepper has a configuration interface with a bidirectional UART port that is connected to a pin on the A64. The GPIO bit-banging functionality of Klipper is used to communicate with the stepper drivers.

Here is a table with pins and addresses for the steppers

Stepper driver config
Name	Pins	Address
S0	PE16	0
S1	PE16	1
S2	PE16	2
S3	PE16	3
S4	PD24	0
S5	PD24	1
S6	PD2	0-3
S7	PD3	0-3

External stepper drivers

It is possible to connect up to two external stepper drivers to Recore in addition to the 6 divers installed on the board. These can be connected using the headers S6 and S7.

See also Restep_A1 for a convenient alternative external stepper driver.

Temperature inputs

4 different temperature devices can be connected to the 4 analog inputs on Recore. Thermistor, Thermocouple, PT100 with INA826 and PT1000 without the use of a pre-amplifier.

Thermistor

Make sure the pull-up is enabled and the op-amp gain is set to 1.

Thermocouple

Make sure the pull-up is disabled and the op-amp gain is set to 100.

[recore]
...
gain_t0: 100
pullup_t0: 0
offset_t0: 1

[Extruder]
...
sensor_type: Type K

PT100 with INA826

In order to use a PT100 sensor, an external amplifier board must be used. There is an example configuration for Klipper that uses this. The ADC reference voltage is 5.0 by default, but for Recore it is 3.3 V. Here is an example:

[Extruder]
...
sensor_type: PT100 INA826
adc_voltage: 3.27

The pull-up must also be disabled.

PT1000

Make sure the pull-up is enabled and the gain is set to 1. In the latest version, the sensor must be prefixed with RECORE.

[Extruder]
...
sensor_type: PT1000
pullup_resistor: 4750

Connecting other sensors

The board has been designed to work with a range of 3rd party sensors for automating the print.

BLtouch

There are two versions of the BLtouch, the difference is the color of one of the GND wires.

The Creality version has a blue GND wire.

Note

There have been some cases of bad quality control for the Creality BLTouches, where the pinout on the sensor side have not matched the color coding in the photos/documentation. It might be good to make sure the color codes match up. For the Creality it should be, from left to right: Blue, red, yellow, black, white.

When connected per wiring diagram above, setting up BLtouch can be done by adding the following section to printer.cfg.

[bltouch]
sensor_pin: ar100:PH6
control_pin: !PB3
speed:15
samples:1
pin_move_time: 0.675
sample_retract_dist: 10
probe_with_touch_mode: true
stow_on_each_sample: false
x_offset:29.2
y_offset:-34
z_offset:0

Inductive Sensor

Connect the inductive sensor on ES0. You can choose either 5V or 12V output on the voltage pin. Inductive sensors often come with an industry standard voltage input of 6-36 V. For this reason there is a 12 V LDO (Low drop-out) voltage regulator integrated on the board. This voltage regulator can be output on the V+ pin of the connector marked ES0. If the Input to the board is 12 V, the LDO will supply a lower voltage, around 10.6 or so.

ADXL345

Note

The ADXL345 seems to cause Klipper to shut down when trying to calibrate at a high rate. A workaround is to use a Pi Pico or similar MCU to communicate with the ADXL345, or to lower the rate. It's been tested working at 400, but not 800 which is the recommended minimum.

See also Remove_A1, a convenient finished accelerometer.

A popular accelerometer sensor for doing input shaping with Klipper is the ADXL345. This can be connected to the connectors S6/S7. There is no hardware SPI interface available, but a software implementation in Klipper exists. Note: Only experimental support has been tested for this. https://learn.adafruit.com/adxl345-digital-accelerometer

Config:

[adxl345]
cs_pin: ar100:PL11
spi_software_sclk_pin: ar100:PL10
spi_software_mosi_pin: ar100:PE15
spi_software_miso_pin: ar100:PE14
rate: 400

[resonance_tester]
accel_chip: adxl345
probe_points:
    100, 100, 20  # an example

Using a Raspberry Pi Pico:

[adxl345]
cs_pin: pico:gpio17
spi_bus: spi0c

Neopixels

To use neopixels, the STM32F031 chip onboard needs to have the bitbanging SPI support compiled in. To do so, follow the steps below to recompile and flash the stm32 chip. Make sure you're not printing while doing any of these!

1. Edit /home/debian/klipper/src/stm32/Kconfig: change the line that reads

   default 0x4000 if MACH_STM32F031

   to

   default 0x8000 if MACH_STM32F031

   This is because the STM32F031 used on the A7 board has double the amount of memory as the one used on A6 boards, and you need this extra space for additional features used by Klipper.
2. Run make menuconfig from the /home/klipper directory. Set the options according to those listed here, except you want to add Support for GPIO "bit-banging" devices under the Optional features menu.
3. Run make clean
4. Run make -j
5. Run cp out/klipper.bin /opt/firmware/stm32.bin
6. Run sudo flash-stm32

Use endstop ES1 (PB3) or ES2 (PB6). Make sure to use a 100 ohm pull-up from pin S (pin 2) to pin 5V (pin 3)

[neopixel my_neopixel]
pin: PB3

See also Relit_A0

RC Servo

Endstop 1 and 2 can be used as PWM outputs with 5V levels. Rev A6 is the first board with support for this. More testing and configuration documentation is needed.

Filament runout sensor

Any of the 6 end stops can be used for connecting a filament runout sensor

Software for Recore

Recore comes with the Linux distro Refactor (Armbian) pre-installed on the eMMC. For more instructions about software for Recore, see the Refactor wiki page: Refactor

AR100

Please see: AR100

Manual control and testing

https://wiki.iagent.no/wiki/Manual_control_and_testing

Performance

Start-up time

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

root@recore:~# systemd-analyze
Startup finished in 3.011s (kernel) + 12.292s (userspace) = 15.303s 
graphical.target reached after 11.934s in userspace

eMMC read and write speed

eMMC write speed: 25.3 MB/s

root@recore:~# dd if=/dev/random of=/random.bin bs=1M count=1000
1048576000 bytes (1.0 GB, 1000 MiB) copied, 41.5008 s, 25.3 MB/s

eMMC read speed: 106 MB/s

root@recore:~# dd if=/random.bin of=/dev/null                                                             
1048576000 bytes (1.0 GB, 1000 MiB) copied, 9.86672 s, 106 MB/s

Measured voltages

The final stages of Recore manufacturing consists of testing, calibration and flashing of firmware. The calibration stage measures a number of voltages on the board and classifies the input stages gain and offset. Instruments used:

• 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

5V Buck converter ripple and noise

The 5V step down/Buck converter is a AOZ2153EQI-30. It can provide 8A and has an input voltage range of 12-28V.

Below is a screenshot of the ripple and noise across the the 5V rail with a normal kernel running and pulling 4 A from the USB and with 6 Neopixels connected.

Input stage

When drawing a constant current of 20 A from the bed connector with and without any 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. The maximum board temperature of 100 degrees C is reached after about 10 minutes with no forced convection. Ambient temperature in the room: 20.1 degrees C.

With forced convection (a 92 mm Noctua fan) and a current load of 29 A, the maximum temperature reached after 10 minutes was 87.7 degrees C as measured by the on board thermistor. The thermal camera showed a higher temperature of 98 degrees.

Maximum input voltage

Using 1.5 m test leads and a 26 V bench top PSU (Agilent U8002A) a board has been tested for over voltage issues. This was a problem with Rev A6. No issues were found during testing.

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 28 A at peak, depending on PSU and cables. This is important to consider when setting the current limit with device tree. Below is a trace of the current draw of Recore A7 when the input is enabled. The PSU in use was a PeakTech 6160 (30V/30A) benchtop switchmode PSU. The cables used were Pomona B-24-0 and B-24-2, 24" 18 AWG banana plug test leads.

Over current protection

There are 3 different sensors present in the input stage for making sure the 12-24 V domain on the board does not overheat during startup and operation.

1. The Fast acting over current protection is to ensure that the high power domain is disabled in the case of a short circuit condition.
2. The current limit set in Klipper monitors the continuous current draw. This is now set at 20 A, but can go up to 30 A and still be within the limits of the connectors and input stage mosfets.
3. The over temperature protection monitors the temperature in the input stage and cuts the power if the temperature goes over 110 degrees. The board should not be kept at this temperature for a prolonged period, but during heated bed heat-up, it can be elevated compared to the rest of the print.

Below is a plot of what the current on the input looks like if there is an over current condition on the high power domain as that domain is turned on.

Below is a plot of what the current on the input looks like if there is an over current condition after the input has been turned on.

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

Temperature calibration

A set of experiments have been carried out to calibrate the different sensors using a dry-well calibrator. The reference probe was a Sensing Devices SDL385 PRT. The levels of calibration was: room temperature, 50, 100, 150, and 200 degrees C.

Thermistor

The thermistor in use was a standard EPCOS 100K B57560G104F. This thermistor has a resistance tolerance of 2 %. The value of the pull-up resistor as measured during calibration was 4740.17501. This value seemed to work well at all levels of calibration, although a little on the high side compared to the reference.

PT1000

The PT1000 in use was a Heraeus 31500989 [1] works well. The tolerance class given in the datasheet is "F 0.10 / Class 1/3 B". There are two different tolerances here: F0.10 and one third of Class B. The accuracy looks good at all temperatures, perhaps a bit on the high side if using the calibrated value for the pull-up. During the testing, 10 ohm was subtracted from the calibrated value.

PT100

The PT100 used in the calibration was the E3D PT100 with the INA826 amplifier board. There is no datasheet available for the PT100 sensor and no mention of what tolerance there is on the reference resistors used. Furthermore Klipper expects the reference voltage to be 5V exactly, and there is no way to supply a measured value. Measurements on Recore has shown that the value is often a bit lower due to the PMIC for the 5V output on the "input" ports. 4.979 V has been measured and is likely an expected value.

Thermocouple

Using the calibration values directly will give a slight offset to the thermocouple measurements. The gain and ADC voltage can be used as measured during calibration. It should be in the region of 101 for gain and 3.307 for ADC voltage. As for the offset, that can be increased slightly to compensate for the cold junction temperature difference. For instance, the measured offset for the test board was 0.0032960, but a value of 0.00340 fit the data points well. The measurements were done on T2, so it it possible that the distance from the cold junction caused the offset. The cold junction thermistor is located between T0 and T1.

FAQ

Where can I ask for help?

You can join the Discord: https://discord.gg/bCnp9H5SB5

What comes in the box with the Recore? Specifically, terminal connectors for power, etc?

It's only the board, no cables or connectors. There is a bag of connectors available to purchase in the web shop.

Do I need access to those 3 buttons on the board?

It is not necessary to have access to the three buttons for normal use.

What's the maximum current draw for heat bed?

This has been tested up to 30 A with good cooling using a fan and a heat sink.

I have a gadget that I want to connect with SPI. Is that possible?

On Recore A7, there is support for an SPI peripheral. The pins are broken out on header S6/S7.

What exactly is the role of the AR100 device?

The AR100 handles the fast real-time aspects, mainly the stepper motors and end stops.

What voltage fans are supported?

The same voltage as the input voltage, either 12 V or 24 V. You can experiment with PWM for running lower voltage fans on 24 V input.

Where is the board layout file?

The Layout file will not be available. It is an "open schematic" board, not open source hardware

Where are you shipping from?

Boards are shipping from Norway. Eventually shipping will be from a warehouse in the US

Known hardware issues for rev A8

List of changes from A7 to A8

• Use JST 2 mm connectors.
• Add enable pin on stepper motors
• 8 layer PCB
• Higher current 5V step down (AOZ2153EQI-30 8A)
• Reduce clearance from 0.15 to 0.1 on ground layers
• Recalculated transmission line impedances for lower Radiated emission
• Add more decoupling capacitors on CPUX node
• Add USB-button
• USB1 and USB2 can now draw much more current
• Add 2 kV capacitor on ethernet connector.
• Add Mipi VCC
• Terminating resistor for CK on DDR3
• Move AXP803 to make room for larger HDMI trace distances.
• Faster level shifter for using Neopixels.
• Fatter VREF traces on DDR3
• Fix FUSB pin usage.
• Lower minimum current limit to 17.5 A (max: 82.5)

Migrating Klipper config from A7 to A8

Section [recore]
Before	After
revision: A7	revision: A8

[tmc2209 stepper_x]
Before	After
	enable_pin: !ar100:PL12