NXP S32G: first character is eaten in bootloader shell

[rh-jkangas]

Haven't been able to test this on other hardware, but the first character is consistently eaten on the S32G when starting a bootloader shell:

trees ⚡nxp-s32g-vnp-rdb3-02 ➤ j storage bootloader-shell
[11/03/25 09:21:29] INFO     Setting up flasher bundle files in exporter                                                   client.py:78
[11/03/25 09:21:30] INFO     Power cycling target...                                                                       client.py:37
[11/03/25 09:21:30] INFO     Starting power cycle sequence                                                                 client.py:25
                    INFO     Waiting 2 seconds...                                                                          client.py:27
[11/03/25 09:21:32] INFO     Power cycle sequence complete                                                                 client.py:30
[11/03/25 09:21:32] INFO     Waiting for U-Boot prompt...                                                                  client.py:40
=> echo
Unknown command 'cho' - try 'help'

I think it's safe to rule out an issue on the hardware side since I have a script that automates a full boot sequence (custom U-Boot command -> Linux console login -> command line entry) that worked as expected when using the serial console directly, and on Jumpstarter, it breaks due to this behavior unless I add a throwaway byte to the beginning.

I've also tested it manually to verify the behavior; the character appears to be dropped regardless of if you send it as soon as the U-Boot prompt appears or 15+ seconds after the prompt shows up.

[rh-jkangas]

Noticed when looking at some logs that it might not be the input being eaten, but mangled by a stray nonprintable character. The first part of the log file with control characters rendered:

$ less -fr run-00.log | head
spawn j storage bootloader-shell
[11/11/25 11:16:36] INFO     Setting up flasher bundle files in exporter                                                                                                                                                                                          client.py:79
[11/11/25 11:16:37] INFO     Power cycling target...                                                                                                                                                                                                              client.py:37
[11/11/25 11:16:37] INFO     Starting power cycle sequence                                                                                                                                                                                                        client.py:25
                    INFO     Waiting 2 seconds...                                                                                                                                                                                                                 client.py:27
[11/11/25 11:16:40] INFO     Power cycle sequence complete                                                                                                                                                                                                        client.py:30
[11/11/25 11:16:40] INFO     Waiting for U-Boot prompt...                                                                                                                                                                                                         client.py:40
=> 
Unknown command '' - try 'help'

But taking a look at the hex dump of the prompt, there's an escape (0x1b) after the prompt:

$ xxd run-00.log  | grep -m1 '=>'
00000e40: 5d38 3b3b 1b5c 0d0a 3d3e 201b 3f0d 0a55  ]8;;.\..=> .?..U

I can reproduce this by just hitting the escape key:

=> <ESC>echo hi
Unknown command 'cho' - try 'help'

I'm not sure what's going on with the escape character showing up, but this sounds vaguely familiar... I definitely didn't see it before I started using Jumpstarter though.