I read this post Asus SRT-AC1900 firmware? and it seems that it's true that listing this router as one the supported ones isn't probably right.
But I am trying to attempt installing OpenWRT anyways. Just to see. I am ok if I brick this router; I am using it to learn.
I am a serial port to attempt to change the firmware. So here is my question, when I plug in the serial cable and turn on the router, I see the following line in the console screen "Uncompressing linux... done, booting the kernel." And that is it, no more messages to see on the serial console. I couldn't find any other ways to interact with kernel or the u-boot loader. Is there anything that I can do to give me a way to send commands or override the boot loader to pause it? Should I try my luck with the JTAG route?
That router does not appear to be supported by OpenWrt. Installing an OpenWrt build will likely brick the unit. If you are actually a developer, you can help bring support to this device, but otherwise I would not recommend attempting to install OpenWrt -- you can't just install a "generic" build since all of the routers have unique characteristics.
Your first interactions with your router should be:
finding out if the OEM firmware provides some means to access a login shell (ssh, telnet, serial <-- if possible).
interacting and documenting the bootloader (likely u-boot), checking the existing bootloader variables, trying to understand (and document) how the firmware is booted from flash, checking if there are means to tftpboot and bootm into an initramfs image over the network.
documenting the heck out of the installed OEM firmware, RAM size, flash size/ type and partitioning, GPIO/ interrupt assignments, OEM firmware installing facilities, etc. pp.
backing up everything on your flash, at least twice and keeping it safe.
Maybe you'll be able to test-run similar/ adapted ipq8064 initramfs images in a couple of days, but don't rush, or you'll regret it dearly due to permanent damage (damaging the bootloader and it's very hard to recover/ game-over for NAND flash, damaging calibration data and it's game-over for the WiFi capabilities, …).