WRT1900AC Single User Mode

[chadster766]

I can get into my WRT1900AC using the TTL serial port console in Single User Mode. Then I fire it up into normal operation. Now I can use standard Linux tool for troubleshooting. I just finish figuring this out. I though you might like to see the screenshot below.

If you are interested in finding out how to do this send me a PM.

 

[RogerSC]

I can get into my WRT1900AC using the TTL serial port console in Single User Mode. Then I fire it up into normal operation. Now I can use standard Linux tool for troubleshooting. I just finish figuring this out. I though you might like to see the screenshot below.

In you are interested in finding out how to do this send me a PM.

So opening up the router doesn't void the warranty?

 

[chadster766]

So opening up the router doesn't void the warranty?

No word back from the Linksys team regarding that

Linksys did make it super easy to open the case though and the TTL cable is off the shelf.

This is for developers, advanced users and Information Tech enthusiasts anyway.

 

[RogerSC]

No word back from the Linksys team regarding that

Linksys did make it super easy to open the case though and the TTL cable is off the shelf.

This is for developers, advanced users and Information Tech enthusiasts anyway.

Well, I do have a 3.3V TTL-USB cable for serial console, myself. I'm more reluctant to get into situations where I may have to use it if it means that if something goes wrong with my router that I can't get it fixed.

That's why I'm asking.

 

[chadster766]

You have the USB to TTL serial cable already.

As long as you don't physical break the unit while undoing the two easy access screws or short it electrically you should be good.

The WRT1900AC was advertise as open source ready. How else can you do open source development without serial access to the boot loader?

 

[RogerSC]

Good question, but companies aren't always logical that way. There are times when they don't think through the results of the conditions of their warranties, etc.

 

[chadster766]

Good question, but companies aren't always logical that way. There are times when they don't think through the results of the conditions of their warranties, etc.

Somewhere in the linksys forum I read a user bricked his WRT1900AC experimenting with OpenWRT and a moderator helped him with the RMA.

I found it:

Re: WRT1900AC; May have bricked it...

 

[RogerSC]

Yeah, I saw those, but not having the content of the PM that was sent, I didn't know what was going on, or what the final resolution was, if there was one.

Did you talk with the person who sent the PM, and see what was going on, then?

Thanks.

 

[chadster766]

Yeah, I saw those, but not having the content of the PM that was sent, I didn't know what was going on, or what the final resolution was, if there was one.

Did you talk with the person who sent the PM, and see what was going on, then?

Thanks.

That's a good idea I will ask tomorrow.

 

[sfx2000]

No word back from the Linksys team regarding that

Linksys did make it super easy to open the case though and the TTL cable is off the shelf.

This is for developers, advanced users and Information Tech enthusiasts anyway.

I think as long as one doesn't break the housing or solder on the board, it'll be pretty tough to invalidate a warranty claim...

 

[thiggins]

This is curious. Linksys told me that serial port write was disabled in factory firmware, at least in the original firmware load.

 

[chadster766]

This is curious. Linksys told me that serial port write was disabled in factory firmware, at least in the original firmware load.

Hi Tim,

I can confirm that write does work on the WRT1900AC TTL serial port.

 

[RMerlin]

This is curious. Linksys told me that serial port write was disabled in factory firmware, at least in the original firmware load.

With stock firmware I wasn't able to write anything (I couldn't start a console), however while I was still on the bootloader I had both read/write access on the serial port.

A serial port with only read access would be half useless for custom firmware developers, as it would prevent using the bootloader to recover from a failed/corrupted firmware flash.

 

[thiggins]

With stock firmware I wasn't able to write anything (I couldn't start a console), however while I was still on the bootloader I had both read/write access on the serial port.

That is what is currently supported as Linksys described it to me. Once you start the Linksys firmware, the serial port is disabled.

 

[chadster766]

With stock firmware I wasn't able to write anything (I couldn't start a console), however while I was still on the bootloader I had both read/write access on the serial port.

A serial port with only read access would be half useless for custom firmware developers, as it would prevent using the bootloader to recover from a failed/corrupted firmware flash.

I didn't try loading firmware across the serial port. Below is CLI I have used:

#Load a firmware TFTP into the Primary Image Location
setenv openwrt-armadaxp--jffs2-128k.img
setenv ipaddr 192.168.200.4
setenv serverip 192.168.200.2
run flash_pri_image

#Get into Linux Single User Mode with Linksys Firmware
setenv 'single' 'single'
setenv 'linksys_nandboot' 'nand read $default_load_addr $pri_kern_addr $pri_kern_size; setenv bootargs $console $default_mtdparts root=/dev/mtdblock5 ro rootfstype=$fs_type init=/sbin/init $single; bootm $default_load_addr;'
boot

#From Single User Mode startup WRT1900AC to normal operation
/etc/system/sysinit
/etc/system/wait
/etc/system/once

#Dangerous!!!! This saves boot loader environment variables to NVRAM
saveenv

 

[RMerlin]

That is what is currently supported as Linksys described it to me. Once you start the Linksys firmware, the serial port is disabled.

Gotcha. That makes sense then.

So technically, it's not the serial port itself that is limited, just the stock firmware that offers no bidirectional console support.

They seem quite intent on keeping the stock firmware as closed/blackboxed as possible.

 

[thiggins]

They seem quite intent on keeping the stock firmware as closed/blackboxed as possible.

Yes. I've encouraged them to reconsider this. But for now it is what it is.