I would have thought a call to yield() from any of the user code (nothing like interrupt handler or any sort of callback) would be pretty harmless.. but seemingly I am getting a lot of panic(). The only possibly "odd" thing is it is not called from loop() but rather from setup() (I wrote some code that write to EEPROM so I had thought it prudent to do some yields). Is that not allowed? I am still not very familiar with CONT, and in fact, I used optimistic_yield() instead, thinking that the "can_yield()" call would have protected me, but no so. Right before panic, I can see cont->pc_ret is not 0 and cont->pc_suspend is 0, but I can't figure out what's ETS_INTR_WITHINISR() though I am sure where it is called from, it is not coming from an interrupt handler.

So, is calling from setup() OK? Or am I missing something.

(gdb) stepi
0x40201978 in __yield () at AppData/Local/Arduino15/packages/esp8266/hardware/esp8266/3.1.2/cores/esp8266/core_esp8266_main.cpp:191
191 panic();
(gdb) p *(cont_t *) 0x3fffefb0
$3 = {pc_ret = 0x40255258 <cont_run+52>, sp_ret = 0x3fffef4c, pc_suspend = 0x0, sp_suspend = 0x3ffffcb8, stack_end = 0xffffd0, unused1 = 0, unused2 = 0, stack_guard1 = 4277137406, stack = {4277137406, 4277137406, 0, 4277137406, 1073738080, 1073738032, 12, 4277137406, 1073738080, 1073738032, 8, 0, 1, 4277137406, 4277137406, 4277137406, 4277137406, 4277137406, 4277137406, 1073677020, 1073738032, 1073644492, 64, 1075975873, 1073737977, 4277137406, 38, 4294902280, 1073737952, 63, 4277137406, 4277137406, 4277137406, 4277137406, 4277137406, 4277137406, 4277137406, 4277137406, 4277137406, 4277137406, 4277137406, 4277137406, 4277137406, 4277137406, 0, 117, 0, 1075843432, 0, 1073737977, 1073737977, 1076269367, 1075888592, 25, 1073737952, 1075888592, 1073738080, 1073738032, 8, 4277137406, 4277137406, 4277137406, 4277137406, 1073677020, 1073738032, 8, 1073737952, 1075860040, 1819635523, 1869488228, 1768300660, 1948279918, 2053467497, 543518319, 4277075978, 4277137406, 4277137406, 4277137406, 4277137406, 4277137406, 4277137406, 4277137406, 4277137406, 4277137406, 1073738080, 1073738032, 8, 4277137406, 4277137406, 4277137406, 1073675388, 0, 0, 427, 4277137406, 4277137406, 4277137406, 1073648292, 1073738080, 4277137406, 4277137406, 4277137406, 4277137406, 0, 1073675388, 1073675256, 1712, 1075898584, 1076294196, 1076294191, 1076294185, 1076294179, 1076294173, 1076294168, 1076294162, 1076294157, 1076294152, 1076294146, 1076294140, 1076294134, 1076294128, 1076294120, 1076294093, 1076294088, 1076294083, 1076294077, 1076294071, 1076294065, 1076294057, 1076294052, 1076294046, 1076294040, 1076294033, 1076294027, 1076294021, 1076294015, 1076294009, 1076294003, 1076293997, 1076293991, 1076293986, 1076293980, 1076293974, 1076293968, 1076293962, 1076293956, 1076293949, 1076293942, 1076293936, 1076293931, 1076293925, 1076293919, 1076293913, 1076293908, 1076293903, 1076293897, 1076293892, 1076293886, 1076293880, 1076293874, 1076293850, 1076293825, 1076293820, 1076293815, 1076293808, 1076293801, 1076293794, 1076293787, 1076293780, 1076293773, 1076293766, 1076293759, 1076293752, 1076293745, 1076293738, 1076293731, 1076293724, 1076293719, 1076293688, 1076293683, 1076293676, 1076293653, 1076293648, 1076293641, 1076293636, 1076293631, 1076293624, 1076293617, 1076293594, 1076293571, 1076293564, 1076293559, 1076293552, 1076293545, 1076293540, 1076293517, 1076293494, 1076293489, 1076293484, 1076293477...}, stack_guard2 = 4277137406, struct_start = 0x3fffefb0}