[SOLVED] Lookahead error (and possibly related layer shifting)

[iratecrayons]

I'm trying to investigate a layer shifting problem that happens only after printing for many hours. In doing this, I've noticed a few consistently reported Look Ahead errors in my log.

I cannot say for certain that these are related, since I receive 2 LaErrors several hours apart, but only 1 layer shift and was not on hand to witness that the error and shift happened at the same time.

None the less, the details follow

=== Diagnostics ===
RepRapFirmware for Duet 2 Maestro version 2.02RC3(RTOS) running on Duet Maestro 1.0
Board ID: 08DGM-95762-FD3TD-6JTDD-3SW6S-18AZH
Used output buffers: 3 of 20 (16 max)
=== RTOS ===
Static ram: 22524
Dynamic ram: 95528 of which 0 recycled
Exception stack ram used: 408
Never used ram: 12612
Tasks: NETWORK(ready,456) HEAT(blocked,1300) MAIN(running,3632)
Owned mutexes:
=== Platform ===
Last reset 16:10:15 ago, cause: software
Last software reset at 2018-11-09 19:20, reason: User, spinning module GCodes, available RAM 12600 bytes (slot 3)
Software reset code 0x0003 HFSR 0x00000000 CFSR 0x00000000 ICSR 0x04418000 BFAR 0xe000ed38 SP 0xffffffff Task 0x4e49414d
Error status: 0
Free file entries: 10
SD card 0 detected, interface speed: 15.0MBytes/sec
SD card longest block write time: 5.0ms, max retries 0
MCU temperature: min 35.7, current 36.0, max 36.8
Supply voltage: min 22.6, current 22.9, max 23.1, under voltage events: 0, over voltage events: 0
Driver 0: standstill, read errors 0, write errors 0, ifcount 54, reads 2535, timeouts 0
Driver 1: standstill, read errors 0, write errors 0, ifcount 54, reads 2535, timeouts 0
Driver 2: standstill, read errors 0, write errors 0, ifcount 54, reads 2535, timeouts 0
Driver 3: standstill, read errors 0, write errors 0, ifcount 40, reads 2526, timeouts 9
Driver 4: standstill, read errors 0, write errors 0, ifcount 54, reads 2534, timeouts 1
Driver 5: ok, read errors 0, write errors 0, ifcount 0, reads 0, timeouts 2536
Driver 6: ok, read errors 0, write errors 0, ifcount 0, reads 0, timeouts 2536
Date/time: 1970-01-01 00:00:00
Slowest loop: 4581229.00ms; fastest: 0.12ms
=== Move ===
Hiccups: 0, StepErrors: 0, LaErrors: 2, FreeDm: 240, MinFreeDm: 150, MaxWait: 0ms, Underruns: 0, 0
Scheduled moves: 0, completed moves: 0
Bed compensation in use: mesh
Bed probe heights: 0.000 0.000 0.000 0.000 0.000
=== Heat ===
Bed heaters = 0, chamberHeaters = -1 -1
Heater 0 is on, I-accum = 0.0
Heater 1 is on, I-accum = 0.4
=== GCodes ===
Segments left: 0
Stack records: 2 allocated, 0 in use
Movement lock held by null
http is idle in state(s) 0
telnet is idle in state(s) 0
file is idle in state(s) 0
serial is idle in state(s) 0
aux is idle in state(s) 0
daemon is idle in state(s) 0
queue is idle in state(s) 0
lcd is idle in state(s) 0
autopause is idle in state(s) 0
Code queue is empty.
=== Network ===
Slowest loop: 4581229.00ms; fastest: 0.03ms
Responder states: HTTP(0) HTTP(0) HTTP(0) HTTP(0) FTP(0) Telnet(0) Telnet(0)
HTTP sessions: 1 of 8
Interface state 5, link 10Mbps full duplex
=== Filament sensors ===
Extruder 0 sensor: ok

And the info from the serial port:

(First error)
DDA.cpp(971) tn=63.789 DDA: start=[145.475998 106.597000 139.229996] end=[123.108002 118.694000 139.229996] s=25.429602 vec=[-0.879605 0.475705 0.000000 0.000000 0.000000]
a=590.270813 d=590.270813 reqv=100.837936 startv=16.817129 topv=100.837936 endv=63.788532 sa=8.373676 sd=5.166537
cks=302827 sstcda=1147363319 tstcddpdsc=85807 exac=7694

(Second error)
DDA.cpp(971) tn=28.953 DDA: start=[210.080994 92.476997 229.830002] end=[210.432007 92.358002 229.830002] s=0.370635 vec=[0.947059 -0.321059 0.000000 0.032903 0.000000]
a=630.855957 d=630.855957 reqv=60.000004 startv=20.305973 topv=29.310781 endv=28.953011 sa=0.354114 sd=0.016521
cks=13913 sstcda=1146301974 tstcddpdsc=71917 exac=22
DDA.cpp(971) tn=7.454 DDA: start=[139.722000 165.498993 246.629990] end=[138.919006 165.173004 246.629990] s=0.866642 vec=[-0.926558 -0.376152 0.000000 0.033772 0.000000]
a=614.104492 d=614.104492 reqv=60.000004 startv=27.890314 topv=30.804615 endv=7.454000 sa=0.139272 sd=0.727370
cks=40096 sstcda=1146608198 tstcddpdsc=63662 exac=0

Should I be concerned about these errors?

[dc42]

Thanks for reporting these errors - they are on my list to look at later today.

[dc42]

I've looked at those errors. There are three of them, and they are all caused by small rounding errors. I think it is unlikely that they are causing the layer shifts; however there is a small possibility that they are, so in the forthcoming 2.02RC4 release I have changed the code to avoid that possibility.

[iratecrayons]

@dc42 Thanks for taking a look so quickly.

Since the shifts only happen after 12-24 hours it's been a bit slow to confirm, but in the end it looks like it was caused by a bad cable that otherwise passed a visual inspection of the crimps.

I hope the bug report has helped in other ways at least.