I have NetGear WNR3500Lv2, which I had installed with Oleg wl500 firmware gotten from, which already disappeared in wast of internet.

Wished to update to TomatoUSB, but there was no way to upload firmware through GUI, and all recovery using tftp didn't work for some reason.

Until I found these things mentioned in different places:

nvram get boot_wait

showed off.

nvram get time_wait was 10.

So I did:

nvram set boot_wait on
nvram set time_wait 60
nvram commit

And then I still was unable to install another firmware using tftp2.exe (mentioned in FAQ in NetGear site). So in another post I found:

erase linux

which I think clears flash where Linux image is. That actually made tftp work straight away. Otherwise I suspect I would have bricked my router.