Connecting an SKR3 H723 via SBC in RRF 3.5.0 Onwards | RepRapFirmware for LPC and STM32

How to connect to an SKR3 H723 via SBC

Overview

The SKR3 H723 is a STM32H743 based board.

Warning: There have been a small number of users who have been suffering from random disconnects between the board and the SBC during printing. This has been due to the type of communication connection used by the DuetSoftwareFramework on the SBC to talk to the board being affected by electrical noise from either something on the printer or equipment near by.
There are a number of steps that can be done to limit this issue.
1. Keep the wires between the controller and the Pi short
2. Use either a ribbon cable, or if using jumper wires then use ribbon-style jumper wire strips with the individual conductors separate only at the ends
3. Use multiple ground connections between the two
4. Beware of ground loops. Problems are likely if more than one of the the PSU supplying the controller, the PSU supplying the Pi, and any other equipment that the Pi is connected to (other than via Ethernet) has its signal ground connected to the mains ground in the 3-pin plug that supplies the power. RPi PSUs are usually not grounded. ATX PSUs always are. Meanwell-style PSUs have a ground connection, but it is up to you whether you link mains ground to PSU negative output.
In short, these disconnects may happen to you or they may not. If they happen and you are unable to fix them, then the only remaining options are track down the noise by changing components one by one or switch to using WiFi rather than an SBC.
For STM32 based boards, there is little gain from using an SBC at this current time, especially as ESP32 is now available.

Firmware File

Teamgloomy now generate per board firmware files. The correct file to use for this board is firmware_skr3_h723.bin.
The firmware release includes both SBC and WiFi modes in one. There are 3 methods available to get the board into SBC mode. These are:

There is no SD card detected in the board.
There is no board.txt on the SD card.
There is an entry sbc.loadConfig=true in the board.txt file on the SD card.

These instructions use option 1.

The latest stable firmware files can be found here And the latest unstable firmware files can be found here

Remember to rename it to firmware.bin. Put it in the root of a FAT32 formatted SD card. The maximum size supported card is 32GB.
Load the SD card into the board and power it up (either using USB or 12/24v). Leave it for 1 minute or so and then power the board down. Check the SD card, and if firmware.bin has changed to firmware.cur, then your board has been flashed correctly and an SD card is not required in the mainboard any more.

SBC

Connecting a Single Board Computer, such as a raspberry pi 3B/3B+/4.

Prepare the Raspberry Pi

Follow the instructions detailed here.

Tip: If you want to use a board other than a Raspberry Pi, please follow the guide here

BOM

5 x 100R resistor
jumpers or other ways of connecting to the SKR3 H723

Connecting the SBC to the SKR3 H723

The pinout for the SKR3 H723 can be found here and the schematic for the Duet 3 for reference can be found here. The raspberry pi GPIO pinout can be found here.

The table below shows the pins required on the SBC and what they are connected to on the SKR3 H723. Please ensure that your cables are no longer than 30cm although they should ideally be as short as possible.

SBC Pin	SKR3 H723	Resistor Value
23/BCM11/SPI0 Clk	PB_13	100R
21/BCM9/SPI0 Miso	PB_14	100R
19/BCM10/SPI0 Mosi	PB_15	100R
24/BCM8/SPIO CE0	PB_12	100R
22/BCM25	PC_14	100R
20/GND	GND	None

Prepare the SD Card

Remember, there are 3 methods available to get the board into SBC mode. These are:

There is no SD card detected in the board.
There is no board.txt on the SD card.
There is an entry sbc.loadConfig=true in the board.txt file on the SD card.

This instruction will assume option 1. If any changes to the stock board.txt settings (shown below) are required, these can be made to a board.txt file on the SBC itself. These are then loaded during the startup process. Therefore, an SD card is not required.
The preset configurables are listed below for reference.

board.longName="BTT SKR3 STM32H723"
sdcard.internal.type=2
SPI0.pins={A.5,A.6,A.7}
SPI1.pins={B.13,B.14,B.15}
SPI2.pins={NoPin,NoPin,NoPin}
SPI3.pins={E.14,E.15,E.13}
SPI4.pins={C.5,B.1,B.0}
SPI5.pins={E.9,NoPin,B.1}
SPI6.pins={NoPin,NoPin,NoPin}
SPI7.pins={NoPin,NoPin,NoPin}
SPI8.pins={NoPin,NoPin,NoPin}
stepper.powerEnablePin=NoPin
stepper.enablePins={D.6,D.1,E.0,C.7,D.13}
stepper.stepPins={D.4,A.15,E.2,D.15,D.11}
stepper.directionPins={D.3,A.8,E.3,D.14,D.10}
stepper.numSmartDrivers=5
stepper.TmcUartPins={D.5,D.0,E.1,C.6,D.12}
stepper.spiChannel=3
power.VInDetectPin=NoPin
sbc.TfrReadyPin=C.14
sbc.csPin=B.12
sbc.spiChannel=1
wifi.espDataReadyPin=B.10
wifi.TfrReadyPin=B.11
wifi.espResetPin=C.14
wifi.serialRxTxPins={D.9, D.8}
heat.tempSensePins={A.1,A.2,A.3}

Booting

Turn it all on and, assuming you have followed the steps correctly, the board will boot correctly.

You can either navigate to duet3.local or find the IP address of the rasberry pi using your router. If you don’t have access to that, use something like Fing to scan your network.

Important: DWC with load with an error of DCS not started if the board is not connected to the pi. If the board is connected and you still receive that error then there is an issue with your wiring.

Errors

Please report any disconnects on either the forum or discord.

Editing board.txt

These changes made to board.txt should be made to the board.txt file on the SBC (through DWC) in the system folder (where config.g can be found). If there is no board.txt present, it can be created using DWC.

Drivers

The following line should be added (obviously with the array entries matching your drivers and their locations):

stepper.DriverType = {Tmc2208, Tmc2240, tmc2209, tmc5160, stepdir}

The DriverType array allows for any driver to be used in any slot so there is no order requirement like the previous detection method. The array must also include an entry for each driver slot up to the last one thats populated.
The following list of entries are valid:

none
stepdir
tmc2208
tmc2209
tmc2660
tmc5160
tmc2240

The entry for stepper.numSmartDrivers is preset in the firmware for the number of drivers your board can handle. The number of drivers only needs to be changed if you are adding more drivers using something such as the BTT EXP MOT.

TMC2240 Driver Temperature

TMC2240 drivers support reporting their own temperature, rather than just hot and very hot like the other TMC drivers. To utilise this, add the following line to your config.g

M308 S11 Y"drivers"

This will return the highest temperature reading from any of the drivers, 2240s will return the actual temperature, other drivers will return 0, 100 or 150 (as before).

If you want to know the temperature of a particular driver you need to add the following line (as well as the above):

M308 S12 Y"drivertemp" p"S11.X"

Where x is the driver number that matches the driver number used by M569

Sensorless Homing

Follow the instructions as found here

Uploading your config

Once you’ve connected to the raspberry pi through your router, start to customise your config.g file etc or upload the outputted zip file from the Configurator to the pi using the system tab of DWC.

Changing the SBC hostname

This is an optional step if you only have a single duet3 on your network. It is required if you have more than one SBC configured RRF setup (as each setup on a network needs a unique host name) or you just want to change the name from the default “duet3”.

The name of the printer is its hostname on the network, you will need to connect to the SBC over SSH in order to run the Raspberry Pi configuration utility and change the hostname.

Note: you cannot currently use the gcode command M550 to set your printer hostname, as you can when using a WiFi setup

Connect via ssh
At a command prompt type
```
sudo raspi-config
```
Select “System Options” -> Hostname-> “OK”-> and set the new printername/hostname.
Select “Finish” and reboot.

Note: The hostname must confirm to certain limitations to be valid. Valid characters for hostnames are letters from a to z, the digits from 0 to 9, the hyphen (-).

Once up and running

You will need to PID tune your tools and your bed. Please be aware that bed tuning may take up to an hour and tool tuning normally takes around 15 minutes. If it takes longer, that is also fine as up to 30 cycles may be ran.

To tune the bed, run the following command, changing the temperature (the S value) if a different tuning temperature is required.

M303 H0 S60

To tune each tool, run the following command, changing the temperature (the S value) if a different tuning temperature is required. This proceedure will activate the part cooling fans during the final phase of the tuning process so their effect is taken into account. If your printer has more than one tool, make sure each one of them is tuned.

M303 T0 S220

Once the tuning is complete, either copy the M307 command into the heater definitions or send M500, ensuring you have M501 at the end of your config.g.
If the tuning fails at the end, carry on saving the values as in most cases the outputted values still work correctly.
If the values still result in a heater fault, please refer to this wiki page for information about how to adjust the values manually.

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