Finally got home. I first tried making a USB Close-Case-Debug cable (shoutout to @DHowett and the EC Card for the info), but unfortunately, it didn’t work for me—just got some random garbage output.
So I ended up connecting directly to the EC Debug UART port and finally got some readable output, though unfortunately, it wasn’t very useful:
--- UART initialized after reboot ---
[Image: RO, hx20_v0.0.1-369d3c3 2021-12-13 21:47:58 runner@fv-az209-518]
[Reset cause: reset-pin soft]
[0.000407 I2C Slave init ctrl:3]
[0.001914 KB boot key mask 0]
[0.001986 Inits done]
[0.023142 SW 0x05]
[0.023617 PB init-on]
[0.026945 kblight registered]
VIVALDI keybd disabled on board request[0.028018 Retry Charger init]
[0.028324 reconfigure kbbl complete.]
[0.028838 event set 0x0000000000800000]
[0.029366 KB init state: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --]
[0.031087 PB task 8 = init-on]
[0.034624 PB task [0.035586 PD1 Reset Complete]
8 = init-on, wait 98199]
Co[0.039377 Controller 0 App1 version B:3.4.0.2570]
[0.039860 Controller 0 App2 version B:3.4.0.2570]
nsole is enabled; ty[0.041965 Dead Battery Condition?]
[0.042385 cypd_update_power_status power_stat 0x0]
pe HELP for help.
> [[0.046225 cypd_set_power_state pwr state 3]
0.045612 hostcmd init 0x0000000000800000]
[0.068585 Updating [0.069721 cypd_set_power_state pwr state 3]
SOC Power Limits: PL2 28, PL4 70, Psys 52, Adapter 0]
[0.073362 CYPD 0 Ready!]
[0.074[0.075220 Controller 1 App1 version B:3.4.0.2570]
[0.075709 Controller 1 App2 version B:3.4.0.2570]
196 running with no b[0.078025 Dead Battery Condition?]
[0.078448 cypd_update_power_status power_stat 0x0]
attery and no AC]
[0.082396 cypd_set_power_state pwr state 3]
[0.093142 charge problem: static update, 0x0 -> 0x1 after 0.093120s]
[0.094626 Battery 0% (Display 0.0 %) / ??h:?? to empty]
[0.097015 charge problem: set voltage, 0x0 -> 0x1 after 0.096993s]
[0.100101 charge problem: set mode, 0x0 -> 0x1 after 0.100079s]
[0.105334 cypd_set_power_state pwr state 3]
[0.108822 CYPD 1 Ready!]
[0.129239 Retry Charger init]
[0.136661 PB task 8 = init-on]
[0.136954 PB task 8 = init-on, wait 99707]
[0.159230 running with no battery and no AC]
[0.205621 PD Source supply changed! old=0x0, new=0x02]
[0.215468 CYPD_RESPONSE_PORT_CONNECT 1]
[0.220888 Updating board_set_active_charge_port port 1]
[0.225129 CL: p1 s1 i3000 v5000]
[0.225549 TODO Implement pd_set_new_power_request port 1]
[0.230270 cypd_update_power_status power_stat 0x0]
[0.235419 INTR_REG CTRL:0 TODO Device 0x2]
[0.237369 PB task [0.237911 INTR_REG CTRL:1 TODO Device 0x2]
8 = init-on]
[0.239051 PB task 8 = init-on, wait 98319]
[0.263897 running with no battery and no AC]
[0.337841 PB task 8 = init-on]
[0.338309 PB task 8 = init-on, wait 99533]
[0.363955 running with no battery and no AC]
[0.399369 update charger!!]
[0.401467 Cancel shutdown]
[0.402143 AC on]
[0.415473 charge_request(15400mV, 0mA)]
[0.419491 power state 0 = G3, in 0x0020]
[0.438309 PB task 8 = init-on]
[0.438694 PB task 8 = init-on, wait 99616]
[0.450346 CYPD_RESPONSE_PD_CONTRACT_NEGOTIATION_COMPLETE 1]
[0.455990 Updating board_set_active_charge_port port 1]
[0.460329 CL: p1 s0 i3000 v20000]
[0.460775 TODO Implement pd_set_new_power_request port 1]
[0.465224 cypd_update_power_status power_stat 0x6]
[0.470997 INTR_REG CTRL:0 TODO Device 0x2]
[0.476485 INTR_REG CTRL:1 TODO Device 0x2]
[0.538906 PB task 8 = init-on]
[0.539316 PB task 8 = init-on, wait 99591]
[0.556130 Updating SOC Power Limits: PL2 40, PL4 45, Psys 57, Adapter 60]
[0.639666 PB task 8 = init-on]
[0.640192 PB task 8 = init-on, wait 99475]
[0.740297 PB task 8 = init-on]
[0.740694 PB task 9 = recovery, wait 199995]
[0.941466 PB task 9 = recovery]
[0.941875 PB task 0 = idle, wait -1]
[4.474227 BB PCH PWR down]
Got Mainboard Power Button event[8.997789 power button pressed]
[8.998219 PB pressed]
[8.998463 PB task 1 = pressed]
[8.998788 BTN wait RSMRST to asserted]
[8.999099 PB task 1 = pressed, wait 19365]
[8.999714 power state 5 = G3->S5, in 0x0020]
[9.000114 setup s5 power up!]
[9.019241 PB task 1 = pressed]
[9.020320 BTN wait RSMRST to asserted]
[9.020632 PB task 1 = pressed, wait 18610]
[9.039716 PB task 1 = pressed]
[9.040126 BTN wait RSMRST to asserted]
[9.040437 PB task 1 = pressed, wait 19280]
[9.047716 SW 0x07]
[9.060322 PB task 1 = pressed]
[9.060815 BTN wait RSMRST to asserted]
[9.061127 PB task 1 = pressed, wait 19196]
[9.071664 can't read any temp sensors!]
[9.072229 can't read any temp sensors!]
[9.080799 PB task 1 = pressed]
[9.081254 BTN wait RSMRST to asserted]
[9.081565 PB task 1 = pressed, wait 19235]
[9.101405 PB task 1 = pressed]
[9.101802 BTN wait RSMRST to asserted]
[9.102242 PB task 1 = pressed, wait 19164]
[9.121881 PB task 1 = pressed]
[9.122412 BTN wait RSMRST to asserted]
[9.122724 PB task 1 = pressed, wait 19157]
[9.142358 PB task 1 = pressed]
[9.142837 BTN wait RSMRST to asserted]
[9.143149 PB task 1 = pressed, wait 19209]
[9.162835 PB task 1 = pressed]
[9.163289 BTN wait RSMRST to asserted]
[9.163601 PB task 1 = pressed, wait 19234]
[9.183441 PB task 1 = pressed]
[9.203925 PB PCH pwrbtn=LOW]
[9.204289 PB task 10 = was-off, wait 479152]
[9.224426 Cancel shutdown]
[9.224823 PH G3S5->S5]
[9.225077 power state 1 = S5, in 0x0071]
[9.225580 PH S5]
Got Mainboard Power Button event[9.437960 power button released]
[9.438264 PB ignoring change]
[9.461233 SW 0x05]
[9.684071 PB task 10 = was-off]
[9.684468 PB released]
[9.684824 PB task 6 = released]
[9.685296 PB PCH pwrbtn=HIGH]
[9.685570 PB task 0 = idle, wait -1]
[10.072458 can't read any temp sensors!]
[10.072965 can't read any temp sensors!]
[10.225869 power state 5 = G3->S5, in 0x0071]
[10.226545 power state 1 = S5, in 0x0071]
[10.226933 PH S5]
[11.073028 can't read any temp sensors!]
[11.073656 can't read any temp sensors!]
[11.227233 power state 5 = G3->S5, in 0x0071]
[11.227875 power state 1 = S5, in 0x0071]
[11.228262 PH S5]
[12.073495 can't read any temp sensors!]
[12.074117 can't read any temp sensors!]
[12.228563 power state 5 = G3->S5, in 0x0071]
[12.229201 power state 1 = S5, in 0x0071]
[12.229588 PH S5]
[13.073960 can't read any temp sensors!]
[13.074577 can't read any temp sensors!]
[13.229888 power state 5 = G3->S5, in 0x0071]
[13.230519 power state 1 = S5, in 0x0071]
[13.230906 PH S5]
[14.074580 can't read any temp sensors!]
[14.075221 can't read any temp sensors!]
[14.231207 power state 5 = G3->S5, in 0x0071]
[14.231832 power state 1 = S5, in 0x0071]
[14.232219 PH S5]
[15.075038 can't read any temp sensors!]
[15.075645 can't read any temp sensors!]
[15.232519 power state 5 = G3->S5, in 0x0071]
[15.233138 power state 1 = S5, in 0x0071]
[15.233525 PH S5]
[16.075497 can't read any temp sensors!]
[16.076100 can't read any temp sensors!]
[16.233825 power state 5 = G3->S5, in 0x0071]
[16.234437 power state 1 = S5, in 0x0071]
[16.234825 PH S5]
[17.075956 can't read any temp sensors!]
[17.076552 can't read any temp sensors!]
[17.235253 power state 5 = G3->S5, in 0x0071]
[17.235860 power state 1 = S5, in 0x0071]
[17.236247 PH S5]
[18.076416 can't read any temp sensors!]
[18.077006 can't read any temp sensors!]
[18.236675 power state 5 = G3->S5, in 0x0071]
[18.237242 power state 1 = S5, in 0x0071]
[18.237757 PH S5]
[19.076875 can't read any temp sensors!]
[19.077459 can't read any temp sensors!]
[19.238022 timeout waiting for S5]
[19.238464 power state 10 = S5->G3, in 0x0071]
[19.239015 PH S5G3]
[19.240830 power state 0 = G3, in 0x0020]
[23.242284 BB PCH PWR down]
[24.078949 Boot issue: HW 0x00000612 BIOS: 0x0000]
I’ll keep digging.