[Fire TV Original Android Development] fabian19vs:
this time I tried without the otg, after the bootrom step, I connected to the TV and it was the "hacked fastboot mode", then after the fastboot step, the loop comes again and sometimes a => RECOVERY mode, and the adb shell gives error. This time everithing was made with the stick connected to the computer (booted from the USB with the fireISO) .

when powering the OTG, I have tried several, the computer's USB, a 5V 1Amp adapter, and a powered USB hub. But for some reason, the red light of the mouse works just for about half a second when the stick is booting, when the logo appears in the screen, it is already off... but I tried the OTG with another working stick and it works good

[root@sysresccd ~/Downloads/kama/kamakiri-mantis-v1.2/kamakiri]# sudo ./bootrom-step.sh
[2021-02-17 06:47:03.502876] Waiting for bootrom
[2021-02-17 06:48:20.424305] Found port = /dev/ttyACM0
[2021-02-17 06:48:20.424821] Handshake
[2021-02-17 06:48:20.425478] Disable watchdog

* * * If you have a short attached, remove it now * * *
* * * Press Enter to continue * * *

[2021-02-17 06:48:27.451878] Load payload from ../brom-payload/stage1/stage1.bin = 0x27C bytes
[2021-02-17 06:48:27.485075] Let's rock
[2021-02-17 06:48:27.491691] Waiting for stage 1 to come online...
[2021-02-17 06:48:27.494385] All good
[2021-02-17 06:48:27.494604] Load 2nd stage payload
[2021-02-17 06:48:27.494725] Load payload from ../brom-payload/stage2/stage2.bin = 0x36D4 bytes
[2021-02-17 06:48:27.494792] Send 2nd stage payload
[2021-02-17 06:48:27.519155] Party time
[2021-02-17 06:48:27.520661] Waiting for stage 2 to come online...
[2021-02-17 06:48:27.774322] All good
[2021-02-17 06:48:27.776204] Check GPT
[2021-02-17 06:48:27.896170] gpt_parsed = {'lk': (1024, 2048), 'tee1': (3072, 10240), 'tee2': (13312, 10240), 'boot': (23552, 32768), 'recovery': (56320, 32768), 'logo': (89088, 7168), 'kb': (96256, 2048), 'dkb': (98304, 2048), 'MISC': (100352, 2048), 'vendor': (102400, 307200), 'system': (409600, 2252800), 'cache': (2662400, 1048576), 'userdata': (3710976, 11558879), '': (0, 1)}
[2021-02-17 06:48:27.896515] Check boot0
[2021-02-17 06:48:27.938170] Check rpmb
[2021-02-17 06:48:28.142507] Clear preloader header
[4 / 4]
[2021-02-17 06:48:28.238919] Downgrade rpmb
[2021-02-17 06:48:28.241108] Recheck rpmb
[2021-02-17 06:48:29.119743] rpmb downgrade ok
[2021-02-17 06:48:29.120865] Flash tz
[7265 / 7265]
[2021-02-17 06:50:10.402089] Flash lk
[613 / 613]
[2021-02-17 06:50:19.020518] Flash lk-payload
[6 / 6]
[2021-02-17 06:50:19.147044] Inject microloader
[2 / 2]
[2021-02-17 06:50:19.293376] Force fastboot
[2021-02-17 06:50:19.386851] Flash preloader
[294 / 294]
[2021-02-17 06:50:28.692371] Reboot
[root@sysresccd ~/Downloads/kama/kamakiri-mantis-v1.2/kamakiri]# sudo ./fastboot-step.sh
Sending 'recovery' (11592 KB) OKAY [ 0.565s]
Writing 'recovery' OKAY [ 0.725s]
Finished. Total time: 1.301s
OKAY [ 0.002s]
Finished. Total time: 0.002s

Your device will now reboot into TWRP.

[root@sysresccd ~/Downloads/kama/kamakiri-mantis-v1.2/kamakiri]# adb shell
error: no devices/emulators found
[root@sysresccd ~/Downloads/kama/kamakiri-mantis-v1.2/kamakiri]# adb devices
List of devices attached

[root@sysresccd ~/Downloads/kama/kamakiri-mantis-v1.2/kamakiri]#