My first post on a great forum. Here are my questions. I bought a used Linksys EA7500 v1 recently and it appears to have the GPG-signed firmware that keeps me from flashing OpenWrt. I have gone to a serial recovery for the first time ever, and I can get U-boot going but can't stop it from going to Autoboot. I've been trying the second way shown in the wiki (https://openwrt.org/toh/linksys/linksys_ea7500_v1?s[]=ea7500), using the 1.8V interface. I have time enough to stopAutoboot, but no matter what key(s) I press, or when I press them, it goes. One thing along the way--I did a poor job of desoldering and don't have much contact surface in the pads to show voltage (just using TX, RX, and GND, not VCC). What's funny is that there is a fair amount of copper exposed and I can easily get continuity from one contact to another, but not voltage. Anyway, the voltage was about 1.8 when I could find those magic spots, but it started to go up, and when I inadvertently touched the board there was a spark. I think that was when it went up quite a bit to 2.28-2.3, and there it stays. So I'm wondering whether I damaged a chip or something like that, and if there's a way to recover.
It might be the USB serial adapter, which shifts voltages to 5v, 3.3, and 1.8, but I can run a Raspberry Pi on it and get an SSH terminal from U-boot. Or maybe I just don't know what I'm doing. Well, I definitely don't. I've tried different static IPs on the PC, 192.168.1.2 and 192.168.1.254, with no more luck one way than another, and I've tried Putty on Windows, and Picocom and Minicom on Linux. I'm also wondering whether I could try the first of the methods outlined on the wiki, but I would have to get resistors and transistors, and maybe it wouldn't make any difference anyway. My real hope is that I just don't know enough and missed a setting, but I don't know how likely that is.
Does anyone have any suggestions? I've seen and read a number of posts on the EA7500 v1, but I don't think I've seen anything that addresses this issue. Thank you very much in advance.
Edit: I just tried the serial adapter using the 3.3v jumper, given that my voltages read well above 1.8, and it looks like I got the same output from U-boot (although I haven't compared closely with the previous). Might this be a sign that it's a problem with the adapter?
I did, thank you, but I think that I got the GPG-signed version of that version, and at that point I didn't realize that would be a problem. I appreciate the question.
I do have some ea7500V1 's & an EA8500
but as I'm outside the US in Australia
I didn't have any problems of signed firmware
I think I did recover an ea8500 once
and I only had a 3.3v usb adapter at the time
so I'm sure I used that
I would have imagined I check the voltage on the vcc pin
but maybe I didn't just expected it to be 3.3V
there is a risk of the 3.3V TX to 1.8V RX pin could brake something
but even 10K resister should limit the current & allow the catch diodes
to protect the 1.8V input I would hope the pcb or adapter has this on it anyway
I used putty on windows
you should be able to check looping back the tx to rx on the serial adapter
to check the adapter & software interaction & terminal echo state etc
I'll try to test the adapter. I am wondering if the spark I mentioned in my original post might have been something, perhaps a resistor, blowing, given that the voltage went from 1.8 to 2.3. But maybe those two things are unrelated. Thank you again.
Yes, the in the wiki (above) one image shows the ones I have tried (1.8), and the second the other set, which requires resistors and transistors to bring it up to 3.3v. But I am thinking that maybe without anything extra it will work at 1.8.
that page is very hard to read and make sense of about the serial port
In the 1st few lines it says
"3.3v logic" on the connector
but to use 3.3v (needs unsoldering and additional elements)
what ?
is it 3.3v logic or 1.8v logic with a 3.3v feed ?
needs to be fixed up i think
You mentioned GPG-signed firmware so I assume you have a US model. Yes, you can't flashing OpenWrt through Netgear's GUI. Just a couple of weeks ago, I went through the TFTP+serial method with my US-model EA7500v1 but I didn't have to mess around with desoldering. My serial I/F is 3.3v and I simply attached the serial I/F pins to the pin header (TX, RX and Ground) as shown in the wiki "Serial connector JM1 (3V3)" photo. Above the photo, the wiki has the statement " Flashing is possible with 3.3V uart (needsunsoldering and additional elements) and 1.8V uart (easier way, no unsoldering)." I think the statement is confusing, and possibly, is wrong. Maybe someone can chime in.
Thank you for that. I think you're right that it is confusing. My impression from reading various threads is that if the pins are already there you don't need to do any desoldering or soldering, but if they aren't you do in order to raise the voltage to 3.3. What I'm thinking is that maybe I can desolder without adding the resistors and transistors, and install at 1.8v.
Sorry, I missed this post at first. As I mentioned to rwl408, my impression is that whether you have to unsolder and add elements depends on whether the pins are there or not. If they are, it's already at 3.3, and if not, you have to add the elements to get it there (from 1.8?). But that's just my impression. I've been wrong before.
the best thing to do
it to use a oscilloscope on the pins going to the processor
work out what it's voltage its using
on it's data sheet find out the recommenced logic levels needed
and see what you have and adjust it to match
keeping in mine that most TTL serial line are inverted
in the translation
idle state is high say 3.3V but that is translated to ~ -10
and the active state 0V is translated to ~ +10
I'm afraid I don't have an oscilloscope. Also, I don't really understand the logic levels; I fear I'm out of my depth here. I do appreciate the suggestion, though.