In my quest to setup auto squaring on my Lead machine, the makers of xPro suggested that I re-compile the firmware enabling the A axis limit switch as Y2. This worked great for the auto squaring function. I now have the 4 limit switches working a treat and auto-squaring is working perfectly. Only trouble is when I send an M3 to fire up the spindle my controller goes into panic and continually reboots. With the pre-compiled firmware it works fine. Spindle is connected via VFD using 0-10V I compiled using the latest Arduino IDE I used the latest CNC Pro Source from GitHub - CNCxPROv5_20210708 Installed the board using boards manager - https://raw.githubusercontent.com/espressif/arduino-esp32/gh-pages/package_esp32_index.json I used GRBL_ESP32 source from GitHub - bdring/Grbl_Esp32: A port of Grbl CNC Firmware for ESP32 The only modifications I made to the source were the machine name, changing the A limit switch name to Y2 as instructed by SparkConcepts and changed the eStop from NO to NC as per src comments. When I send an M3 to the controller the spindle starts, but then the controller panics and restarts. Therefore I cannot sent and M5, I have to hit the eStop and reset the controller. Here is the console error: Guru Meditation Error: Core 1 panic'ed (Cache disabled but cached memory region accessed) Core 1 register dump: PC : 0x400df294 PS : 0x00060034 A0 : 0x80081680 A1 : 0x3ffc0670 A2 : 0x00000000 A3 : 0x00000000 A4 : 0xfffffff7 A5 : 0x3ffd1840 A6 : 0x00000020 A7 : 0xffffffe7 A8 : 0x8008157d A9 : 0x00000001 A10 : 0x00060820 A11 : 0x00000000 A12 : 0x15122500 A13 : 0x00060820 A14 : 0x00000003 A15 : 0x00060823 SAR : 0x0000001a EXCCAUSE: 0x00000007 EXCVADDR: 0x00000000 LBEG : 0x4000c2e0 LEND : 0x4000c2f6 LCOUNT : 0x00000000 Core 1 was running in ISR context: EPC1 : 0x4008ee9c EPC2 : 0x00000000 EPC3 : 0x00000000 EPC4 : 0x400df294 ELF file SHA256: 0000000000000000 Backtrace: 0x400df294:0x3ffc0670 0x4008167d:0x3ffc0690 0x4008e571:0x3ffc06b0 0x4008ee99:0x3ffd1880 0x4008f33d:0x3ffd18a0 0x4021a5e1:0x3ffd1910 0x40218da1:0x3ffd1930 0x402191e3:0x3ffd1950 0x40217b27:0x3ffd19c0 0x40218542:0x3ffd1a10 0x402172f1:0x3ffd1a70 0x401d0a25:0x3ffd1ab0 0x401d0b0a:0x3ffd1af0 0x401d0b31:0x3ffd1b10 0x400fe55b:0x3ffd1b30 0x400fe677:0x3ffd1b50 0x401f9993:0x3ffd1b70 0x400eef7d:0x3ffd1b90 0x400eacde:0x3ffd1c90 0x400eaf51:0x3ffd1d00 0x400d3fe8:0x3ffd1d20 0x400d2613:0x3ffd1d40 0x400fc22a:0x3ffd1d60 0x40091d02:0x3ffd1d80 I can provide source files if required. Any ideas where this has gone wrong