Hi,
I’m trying to get Remora to work with a Raspberry Pi 4
Compute Module (on the official IO board) and a BTT SKR 1.4 (LPC1768) board via SPI (using EXP2 directly).No matter what I do, I keep getting “bad spi payload” errors and I can’t reset estop in LinuxCNC. The estop status toggles randomly, sometimes reporting errors like “fffff”, “3a”, “71”, then “0”, but it never clears or lets me enable the machine.
Here’s what I’ve already tried:
- Double/triple-checked config files (.hal/.ini/config.txt) for base/servo thread values and SPI freq
- Tried SPI_FREQ values from 40000 down to 2500
- Used multiple different SD cards, freshly copied firmware/config.txt every time
- Swapped and powered from two different power supplies, always with common ground
- Used short (10–20 cm) jumper wires and a dedicated IDC ribbon cable between RPi CM4 IO board and SKR (connected to SPI0 CS0)
- Confirmed CS line matches config and wiring
- Tried wiring both loosened and via the screw-terminal “HAT”
- Tested with two different RPi modules
- Flashed the correct Remora firmware for LPC1768, config.txt matches hardware
Symptoms – what I see:
- LinuxCNC starts, RPi and SKR both power up
- E-stop never disengages, status bits change randomly
- Console/log shows many “bad spi payload” errors, with hex codes changing each time
- Stepper drivers do not respond, SPI module loads but does not work
My setup:
- Raspberry Pi 4 Compute Module on official IO board
- BTT SKR 1.4 (LPC1768) with Remora firmware
- Connecting via SPI (EXP2 header), CS0
- Cables all short, tried IDC and normal dupont/jumper types
Questions:
- Is there anything obvious I’m missing in configs or wiring?
- Has anyone had this persist even with good IDC cable and CM4?
- Any proven working “plug-and-play” cable or adapter for this combo?
- Are there common hardware quirks or firmware issues with this setup?
- Would using a logic analyzer or scope help, and what to look for?
I’m attaching my
,
and
files plus a photo of my wiring. Any advice, example configs, or troubleshooting steps would be greatly appreciated!
.hal file:
# Load the realtime components loadrt [KINS]KINEMATICS loadrt [EMCMOT]EMCMOT base_period_nsec=[EMCMOT]BASE_PERIOD servo_period_nsec=[EMCMOT]SERVO_PERIOD num_joints=[KINS]JOINTS loadrt remora-spi SPI num=0 CS_num=0 SPI [remora]SPI_FREQ=20000 # estop loopback, SPI comms enable and feedback net user-enable-out <= iocontrol.0.user-enable-out => remora.SPI.enable net user-request-enable <= iocontrol.0.user-request-enable => remora.SPI-reset net remora-status <= remora.SPI-status => iocontrol.0.emc-enable-in # add the remora and motion functions to threads addf remora.read servo-thread addf motion-command-handler servo-thread addf motion-controller servo-thread addf remora.update-req servo-thread addf remora.write servo-thread # Joint 0 setup setp remora.joint.0.scale [JOINT_0]SCALE setp remora.joint.0.maxaccel [JOINT_0]STEPGEN_MAXACCEL net x:pos-cmd <= joint.0.motor-pos-cmd => remora.joint.0.pos-cmd net x:pos-fb <= remora.joint.0.pos-fb => joint.0.pos-fb net x:enable <= joint.0.amp-enable-out => remora.joint.0.enable # Joint 1 setup setp remora.joint.1.scale [JOINT_1]SCALE setp remora.joint.1.maxaccel [JOINT_1]STEPGEN_MAXACCEL net y:pos-cmd <= joint.1.motor-pos-cmd => remora.joint.1.pos-cmd net y:pos-fb <= remora.joint.1.pos-fb => joint.1.pos-fb net y:enable <= joint.1.amp-enable-out => remora.joint.1.enable # Joint 2 setup setp remora.joint.2.scale [JOINT_2]SCALE setp remora.joint.2.maxaccel [JOINT_2]STEPGEN_MAXACCEL net z:pos-cmd <= joint.2.motor-pos-cmd => remora.joint.2.pos-cmd net z:pos-fb <= remora.joint.2.pos-fb => joint.2.pos-fb net z:enable <= joint.2.amp-enable-out => remora.joint.2.enable
.ini file:
# Basic LinuxCNC config for testing of Remora firmware [EMC] MACHINE = Remora-XYZ DEBUG = 0 VERSION = 1.1 [DISPLAY] DISPLAY = axis EDITOR = gedit POSITION_OFFSET = RELATIVE POSITION_FEEDBACK = ACTUAL ARCDIVISION = 64 GRIDS = 10mm 20mm 50mm 100mm MAX_FEED_OVERRIDE = 1.2 MIN_SPINDLE_OVERRIDE = 0.5 MAX_SPINDLE_OVERRIDE = 1.2 DEFAULT_LINEAR_VELOCITY = 50.00 MIN_LINEAR_VELOCITY = 0.00 MAX_LINEAR_VELOCITY = 200.00 DEFAULT_ANGULAR_VELOCITY = 36.00 MAX_ANGULAR_VELOCITY = 45.00 INTRO_GRAPHIC = linuxcnc.gif INTRO_TIME = 5 PROGRAM_PREFIX = ~/linuxcnc/nc_files INCREMENTS = 50mm 10mm 5mm 1mm .5mm .1mm .05mm .01mm [KINS] JOINTS = 3 #KINEMATICS =trivkins coordinates=XYZ kinstype=BOTH KINEMATICS = trivkins coordinates=XYZ [FILTER] PROGRAM_EXTENSION = .py Python Script py = python [TASK] TASK = milltask CYCLE_TIME = 0.010 [RS274NGC] PARAMETER_FILE = linuxcnc.var [EMCMOT] EMCMOT = motmod COMM_TIMEOUT = 1.0 COMM_WAIT = 0.010 BASE_PERIOD = 25000 SERVO_PERIOD = 1000000 [HAL] HALFILE = remora-xyz.hal POSTGUI_HALFILE = postgui_call_list.hal [TRAJ] COORDINATES = X Y Z LINEAR_UNITS = mm ANGULAR_UNITS = degree CYCLE_TIME = 0.010 DEFAULT_LINEAR_VELOCITY = 50.00 MAX_LINEAR_VELOCITY = 200.00 NO_FORCE_HOMING = 1 [EMCIO] EMCIO = io CYCLE_TIME = 1.00 TOOL_TABLE = tool.tbl [AXIS_X] MAX_VELOCITY = 250 MAX_ACCELERATION = 750.0 MIN_LIMIT = -5.0 MAX_LIMIT = 300.0 [JOINT_0] TYPE = LINEAR HOME = 0.0 MIN_LIMIT = -5.0 MAX_LIMIT = 300.0 MAX_VELOCITY = 250.0 MAX_ACCELERATION = 750.0 STEPGEN_MAXACCEL = 2000.0 SCALE = 80.0 FERROR = 2 MIN_FERROR = 2.0 HOME_OFFSET = 2.0 HOME_SEARCH_VEL = 0 HOME_LATCH_VEL = 0 HOME_SEQUENCE = 0 [AXIS_Y] MAX_VELOCITY = 250.0 MAX_ACCELERATION = 750.0 MIN_LIMIT = -0.01 MAX_LIMIT = 300.0 [JOINT_1] TYPE = LINEAR HOME = 0.0 MIN_LIMIT = -5.0 MAX_LIMIT = 300.0 MAX_VELOCITY = 250.0 MAX_ACCELERATION = 750.0 STEPGEN_MAXACCEL = 2000.0 SCALE = 80.0 FERROR = 5 MIN_FERROR = 5.0 HOME_OFFSET = 0.0 HOME_SEARCH_VEL = 0 HOME_LATCH_VEL = 0 HOME_SEQUENCE = 0 [AXIS_Z] OFFSET_AV_RATIO = 0.2 MAX_VELOCITY = 5.0 MAX_ACCELERATION = 200.0 MIN_LIMIT = -280 MAX_LIMIT = 280 [JOINT_2] TYPE = LINEAR HOME = 0.0 MIN_LIMIT = -280 MAX_LIMIT = 280 MAX_VELOCITY = 5.0 MAX_ACCELERATION = 200.0 STEPGEN_MAXACCEL = 3000.0 SCALE = 400.0 FERROR = 5 MIN_FERROR = 1.0 HOME_OFFSET = 0.0 HOME_SEARCH_VEL = 0 HOME_LATCH_VEL = 0 HOME_SEQUENCE = 0
config.txt:
{
"Board": "BIGTREETECH SKR v1.3 & v1.4",
"Threads": [
{ "Thread": "Base", "Frequency": 40000 },
{ "Thread": "Servo", "Frequency": 1000 }
],
"Modules": [
{
"Thread": "Servo",
"Type": "Reset Pin",
"Comment": "Reset pin",
"Pin": "1.31"
},
{
"Thread": "Base",
"Type": "SPI",
"Comment": "SPI interface to Raspberry Pi",
"CS Pin": "0.16"
},
{
"Thread": "Base",
"Type": "Stepgen",
"Comment": "X - Joint 0 step generator",
"Joint Number": 0,
"Step Pin": "2.2",
"Direction Pin": "2.6",
"Enable Pin": "2.1"
},
{
"Thread": "Base",
"Type": "Stepgen",
"Comment": "Y - Joint 1 step generator",
"Joint Number": 1,
"Step Pin": "0.19",
"Direction Pin": "0.20",
"Enable Pin": "2.8"
},
{
"Thread": "Base",
"Type": "Stepgen",
"Comment": "Z - Joint 2 step generator",
"Joint Number": 2,
"Step Pin": "0.22",
"Direction Pin": "2.11",
"Enable Pin": "0.21"
}
]
}
