[Fire HD 8 and HD 10 General] spdqbr:
I made it to bootrom-step.sh, and that appears to have run successfully. However now when I try

fastboot reboot recovery

I get the usage message for fastboot:

# ./bootrom-step.sh
[2019-03-04 00:27:18.798732] Waiting for bootrom
[2019-03-04 00:27:26.336656] Found port = /dev/ttyACM0
[2019-03-04 00:27:26.336890] Handshake
[2019-03-04 00:27:26.337276] Disable watchdog

* * * Remove the short and press Enter * * *

[2019-03-04 00:27:56.377687] Init crypto engine
[2019-03-04 00:27:56.395798] Disable caches
[2019-03-04 00:27:56.399726] Disable bootrom range checks
[2019-03-04 00:27:56.410763] Load payload from ../brom-payload/build/payload.bin = 0x4690 bytes
[2019-03-04 00:27:56.412639] Send payload
[2019-03-04 00:27:57.074721] Let's rock
[2019-03-04 00:27:57.075569] Wait for the payload to come online...
[2019-03-04 00:27:57.807523] all good
[2019-03-04 00:27:57.807917] Check GPT
[2019-03-04 00:27:58.164678] gpt_parsed = {'proinfo': (1024, 6144), 'PMT': (7168, 9216), 'kb': (16384, 2048), 'dkb': (18432, 2048), 'lk': (20480, 2048), 'tee1': (22528, 10240), 'tee2': (32768, 10240), 'metadata': (43008, 80896), 'MISC': (123904, 1024), 'reserved': (124928, 16384), 'boot': (141312, 32768), 'recovery': (174080, 40960), 'system': (215040, 6354944), 'vendor': (6569984, 460800), 'cache': (7030784, 1024000), 'userdata': (8054784, 22480863)}
[2019-03-04 00:27:58.164880] Check boot0
[2019-03-04 00:27:58.410125] Check rpmb
[2019-03-04 00:27:58.619520] Downgrade rpmb
[2019-03-04 00:27:58.621743] Recheck rpmb
[2019-03-04 00:27:59.515990] rpmb downgrade ok
[2019-03-04 00:27:59.516232] Flash lk-payload
[4 / 4]
[2019-03-04 00:27:59.847318] Flash preloader
[288 / 288]
[2019-03-04 00:28:06.291277] Inject microloader
[4 / 4]
[2019-03-04 00:28:06.623363] Reboot to unlocked fastboot
root@.../amonet-lite# fastboot reboot recovery
usage: fastboot [ <option> ] <command>

commands:
update <filename> Reflash device from update.zip.
flashall Flash boot, system, vendor, and --
if found -- recovery.
flash <partition> [ <filename> ] Write a file to a flash partition.
flashing lock Locks the device. Prevents flashing.
...

A few things I was able to try:

At this point I have the amazon logo on a black screen:

Holding down the power button shuts off the tablet.

Issuing

fastboot reboot

reboots the tablet to the Amazon logo

Issuing

fastboot reboot-bootloader

reboots the table and I get a black screen with just

=> FASTBOOT mode...

at the bottom

If I shut down the tablet, and rerun the script, I get the following:

# ./bootrom-step.sh
[2019-03-04 00:39:41.574553] Waiting for bootrom
[2019-03-04 00:39:51.413047] Found port = /dev/ttyACM0
[2019-03-04 00:39:51.413639] Handshake
Traceback (most recent call last):
File "/usr/lib/python3/dist-packages/serial/serialposix.py", line 537, in write
n = os.write(self.fd, d)
OSError: [Errno 5] Input/output error

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
File "main.py", line 121, in <module>
main()
File "main.py", line 54, in main
handshake(dev)
File "/home/spdqbr/Fire HD 8 2018/amonet-lite/modules/handshake.py", line 9, in handshake
dev.handshake()
File "/home/spdqbr/Fire HD 8 2018/amonet-lite/modules/common.py", line 97, in handshake
c = self._writeb(b'\xa0')
File "/home/spdqbr/Fire HD 8 2018/amonet-lite/modules/common.py", line 91, in _writeb
self.dev.write(out_str)
File "/usr/lib/python3/dist-packages/serial/serialposix.py", line 571, in write
raise SerialException('write failed: {}'.format(e))
serial.serialutil.SerialException: write failed: [Errno 5] Input/output error

I appear to be stuck from this point. Do you have any suggestions?