[knc1]

Two points:

*) That is a very old thread, and is written about a very simple Kindle (a K2) model. *

*) yifanlu was at one time employed as a lab126 consultant. (not a secret, its in his CV).

With the series 5.x devices, at least the more modern ones based on the i.MX6SL, SoC (which is PW2 or newer) -
You really, really, really want to use a serial port connection.

Prior to loading a boot loader, the SoC only communicates with the serial port.

After loading the boot loader (u-boot is used by Amazon, but there are builds of Redboot for the i.MX6SL also), then the boot loader only communicates with the serial port.

The next thing that loads and runs is the linux kernel, which only communicates via the serial port.
When first loaded, it is running in a memory (ram) resident, initramfs system.
That contains enough code to run the display (for the recovery menu) but its primary communications path is via the serial port.

Once the boot sequence gets past that point and does its 'switch root' command to replace the initramfs file system with the one rooted in an eMMC partition - -
THEN and only then can you bring up USBnetwork (main) or Rescue Pack (diags).

So you should be able to read above that without a serial port, any error you introduce to that very long boot sequence converts your Kindle into a PaperWeight.

You want to install a serial port. You really do.

You also want to get the Kindle network booting, or at least running its filesystem from NFS (the kernel, while still running ram resident, can use an NFS export for its main file system).
Of course, you need a serial port connection to 'talk' u-boot into giving the kernel the proper set of command line arguments when it loads the kernel.

Yes, you want a working serial port.

You can probably get away without a JTAG setup.

- - - - -

* For instance, the K2 was long before Kindle devices became dual boot machines.

= = = =

In general, replacing the Amazon OS is a very bad idea (tm).

Replacing any embedded system with a non-embedded system is an even worse idea.

If you feel you need more memory, there are a lot of the Amazon services specific to the Kindle that you can just stop.
There are threads here on how to do that on the modern Kindles.

If you still feel you need more memory, set-up and enable swap.
There are threads here on that also.