[goldbeanchina]

I don’t have a wiki account. So I share my experience here. This is for rt-n16 jtag recovery.
Where to order the jtag adaptor or cable:
http://www.diygadget.com/jtag-cables/universal-jtag-adapter-v2-wiggler-and-xilinx-platform-cable-compatible-debrick-routers-modems-and-more.html
It has everything u need wires and pins.

Solder pins according to pin layout @ http://www.dd-wrt.com/wiki/index.php/JTAG_pinouts#Asus_RT-N16
I only soldered TDI, TDO, TMS, TCK &GND.
Wire up the jtag adaptor using buffer mode according to the diagram here: http://www.tiaowiki.com/w/Universal_JTAG_User_Manual_%28Parallel%29#Buffered_mode
In this web page, The pcb layout is not the same as the one I received. But the pins are labeled correctly. So it is ok.
Connect only TDI, TDO, TMS, TCK &GND from router to adaptor.

Plugin mini usb to the jtag adaptor and plug the adaptor to pc’s LPT port.

I use win7 and the software is from http://sourceforge.net/projects/tjtag/files/
I always use these switches for rt-n16: /noreset /nodma /byte_mode
For my case, it is easy. I only want to fix the nvram entry I messed up. I backup nvram and use hex editor and change clkfreq to the right value, and flash it back. My trusted rt-n16 is back. ^_~

Hope this is helpful for anyone who may decide to use jtag before trying replace NAND chip.

[Magnetron1.1]

@goldbeanchina: Congratulations on restoring your router.

I repeated your clkfreq experiment and found an easier and much faster way to recover. (JTAG flashing a 128KB NVRAM file requires about 1 hour and 54 minutes.)

Here's what worked for me:

• At a command line prompt enter: tjtag3 -erase:nvram /byte_mode <=== Executes in 1 second!
  
• Power cycle the router which causes the CFE to restore default values (i.e. clkfreq=480,240,120) to the NVRAM partition and allows the router to successfully boot.
  
• Use the router's WebGUI to restore a good, previously saved config file.

Here's a helpful wiring diagram for the TIAO Version 2 Universal JTAG PCB: (Click on image to make bigger in a new browser tab)


Download larger image from here.

- Magnetron1.1

[goldbeanchina]

Yours is definitely the preferred approach.

The reason I'd like to restore the modified Nvram is because that I do not have a recent backup, I am very lazy to go through the manually setup for VPN firewall rule and other things, Should have done the nvram backup more frequently.

BTW, the wiring diagram is wonderful.

[Milkman00]

Well I was lead here when my RT-N16 was bricked and couldn't be recovered. I am a little confused. I just bought this on eBay, but it doesn't look like this can be used to JTAG a router (this is my first time having to JTAG):

http://www.ebay.com/itm/261037239122

Will that not work to perform a JTAG??? Am I going to have to get one of these??

http://www.diygadget.com/universal-jtag-adapter-v2-wiggler-and-xilinx-platform-cable-compatible-debrick-routers-modems-and-more.html

[redhawk0]

your link to Ebay is for a Serial setup...not JTAG...get the one from diy.

redhawk

[Milkman00]

Thanks. What would a serial setup accomplish for this router, since I do see TX and RX pins on the main board?

[Milkman00]

[mstombs]

My Asus routers have serial pin header factory fitted. I assumed they all would and they use them for factory test before shipping?