Configuration

This page covers the minimum printer.cfg needed to get an Ouroboros board recognized by Klipper, ready for FOCI_SELFTEST and FOCI_SETUP on both steppers. Ouroboros is a single STM32H723 MCU driving two stepper channels, so it needs one [mcu] section and one [stepper_x]/[foci stepper_x] pair per channel, not two separate MCUs.

Tuned gains, encoder alignment, and everything else that FOCI_AUTOTUNE and FOCI_SETUP persist come from SAVE_CONFIG afterward. None of that belongs in this initial config.

MCU

[mcu ouroboros]
serial: /dev/serial/by-id/usb-foci_FOCI_Ouroboros_<serial>-if00

Use the serial path you noted down in Installation.

Stepper X and Y

Each axis needs a standard Klipper [stepper_x]/[stepper_y] section (FOCI reads microsteps, rotation_distance, and full_steps_per_rotation straight from it) plus a [foci stepper_x]/[foci stepper_y] section that turns on the TMC4671 driver for that channel. The foci section name must match the linked stepper section’s name exactly; that’s the only thing that links the two.

Channel 0 is STEP0/DIR0/ENA0, channel 1 is STEP1/DIR1/ENA1. Swap which physical stepper you wire to which channel if X and Y come out reversed, rather than trying to swap the pin names.

[stepper_x]
step_pin: ouroboros:STEP0
dir_pin: ouroboros:DIR0
enable_pin: !ouroboros:ENA0
microsteps: 16
full_steps_per_rotation: 200
rotation_distance: 40
# A real endstop is still required by Klipper here. ^PA0 is the
# endstop on your main MCU; alternatively, wire the switch to
# Ouroboros' own STOP0 connector and use ouroboros:STOP0 instead. See
# Sensorless Homing for FOCI's virtual_endstop option.
endstop_pin: ^PA0

[foci stepper_x]
run_current: 1.0
encoder_ppr: 1000

[stepper_y]
step_pin: ouroboros:STEP1
dir_pin: ouroboros:DIR1
enable_pin: !ouroboros:ENA1
microsteps: 16
full_steps_per_rotation: 200
rotation_distance: 40
# Same choice as X: ^PA1 (main MCU) or ouroboros:STOP1 (Ouroboros'
# own connector).
endstop_pin: ^PA1

[foci stepper_y]
run_current: 1.0
encoder_ppr: 1000

Keeping your existing physical endstops

Changing endstop_pin is only necessary if you want to move a switch onto Ouroboros’ own endstop connector. If a switch is already wired to a board you’re keeping, such as a toolhead board, leave it there and leave that axis’s endstop_pin as it is.

Required fields

run_current and encoder_ppr are the only two fields [foci <stepper>] requires.

• run_current is in amps. Start at 50-80% of your motor’s rated phase current from its datasheet, then raise it later if FOCI_AUTOTUNE or your motion tests call for more headroom.
• encoder_ppr is your encoder’s pulses-per-revolution rating, read off the encoder’s or motor’s datasheet or nameplate. It has nothing to do with microsteps or full_steps_per_rotation. The common LDO-42STH48-2504B-EN1000 ships with a 1000 PPR encoder, hence encoder_ppr: 1000 in the example above.

MCU and MOSFET temperature

Ouroboros exposes three analog channels as regular ADC pins: MCU_TEMP (the STM32H723’s internal die temperature) and TH0/TH1 (one MOSFET thermistor per channel). These work with Klipper’s stock [temperature_sensor] support directly:

[temperature_sensor ouroboros_mcu]
sensor_type: Generic 3950
sensor_pin: ouroboros:MCU_TEMP
min_temp: 0
max_temp: 120

[temperature_sensor ouroboros_tmc1_mosfet]
sensor_type: Generic 3950
sensor_pin: ouroboros:TH0
min_temp: 0
max_temp: 100

[temperature_sensor ouroboros_tmc2_mosfet]
sensor_type: Generic 3950
sensor_pin: ouroboros:TH1
min_temp: 0
max_temp: 100

Restart Klipper, then continue with Bring-up.