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Author Topic: Help with GuruPlug JTAG connection  (Read 6211 times)
mookiedog
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« on: May 21, 2010, 06:33:10 PM »

My problem is that my Guruplug and JTAG box does not produce any serial output, although I know that the serial input into the guruplug is working.

Can someone with a Guruplug and a JTAG adaptor do me a favor?

1) connect _just_ the JTAG adaptor to your PC via USB cable (do NOT connect the JTAG to the guruplug)
2) start your serial program (putty or whatever)
3) type characters into the serial program

The question is: when you type characters, do BOTH the TX and RX blue lights flash?  Do the characters you type get echoed to the screen, even if you have local echo disabled?

They do on my setup, even when I have local echo disabled.  It seems to indicate that my JTAG module is echoing the data that it receives.

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big_ignoramus
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« Reply #1 on: May 21, 2010, 08:50:55 PM »

The question is: when you type characters, do BOTH the TX and RX blue lights flash?  Do the characters you type get echoed to the screen, even if you have local echo disabled?

Yes, I see that same behavior when I follow your instructions. I do get serial output from the JTAG and GuruPlug however when it is plugged into my computer's USB port. I'm using Linux so I set my serial port terminal to use /dev/ttyUSB0 or /dev/ttyUSB1 depending on how it shows up. I'm not sure how it shows up in Windows and you might need to install a usb-to-serial driver (such as at http://www.usbserialdrivers.com/ although I haven't tried the files offered there).

Hope that helps.

Edit: Actually you might want to check out this thread: http://plugcomputer.org/plugforum/index.php?topic=1679.0
« Last Edit: May 21, 2010, 09:11:19 PM by big_ignoramus » Logged

mookiedog
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« Reply #2 on: May 21, 2010, 09:46:24 PM »

Thanks for confirming that.

Now I am mystified.  Why does my serial input work, but not the serial output?

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mookiedog
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« Reply #3 on: May 21, 2010, 10:23:38 PM »

> Edit: Actually you might want to check out this thread: http://plugcomputer.org/plugforum/index.php?topic=1679.0

OK, I tried that: no change; still no serial output.
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j.hoekstra
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« Reply #4 on: May 22, 2010, 12:42:21 PM »

> Edit: Actually you might want to check out this thread: http://plugcomputer.org/plugforum/index.php?topic=1679.0

OK, I tried that: no change; still no serial output.
What do you mean by serial output? Seeing the plug boot and being able to give commands?
I noticed that you need to stick the cables in really deep, if your problem is getting no output from the plug check your connection, I put the cable in place and pushed it gently in with a screwdriver(short nails Wink).
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mookiedog
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« Reply #5 on: May 22, 2010, 01:02:26 PM »

> What do you mean by serial output? Seeing the plug boot and being able to give commands?

Exactly: when connected to the console serial port via the optional JTAG box, there is no output -- only input.  I *can* give it commands.  If I hit return a few times after applying power, the plug stays in the uboot command area and does not boot into the blinking WiFi LED stage.  If I don't hit returns after power on, the plug boots all the way. 

After the plug boots, even though I don't get any response from the plug when I type, I know it is doing what I am asking: I can log in by typing the root user name and default root password, and then if I type a 'reboot' command, the plug reboots.

I have a SheevaPlug too, and it works perfectly over the jtag serial console interface.  It's only my guruplug that seems to be JTAG output-challenged.
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j.hoekstra
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« Reply #6 on: May 22, 2010, 01:13:16 PM »

> What do you mean by serial output? Seeing the plug boot and being able to give commands?

Exactly: when connected to the console serial port via the optional JTAG box, there is no output -- only input.  I *can* give it commands.  If I hit return a few times after applying power, the plug stays in the uboot command area and does not boot into the blinking WiFi LED stage.  If I don't hit returns after power on, the plug boots all the way. 

After the plug boots, even though I don't get any response from the plug when I type, I know it is doing what I am asking: I can log in by typing the root user name and default root password, and then if I type a 'reboot' command, the plug reboots.

I have a SheevaPlug too, and it works perfectly over the jtag serial console interface.  It's only my guruplug that seems to be JTAG output-challenged.
I'm just a newbie in the plugworld, but is JTAG-communication defined by specific pins for in and output? Otherwise I'd say your JTAG is defective. I just was really surprised how deep it's pushed in the plug, the whole connector disappears into the housing so to say...
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mookiedog
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« Reply #7 on: May 22, 2010, 01:35:29 PM »

OK, I had serial output working for about 1 minute.  I was wiggling the 4-pin UART cable, and I started getting output.  If I continued to wiggle the cable, the output would come and go.  Now, it completely gone again.  I think it must be either be the cable or one of the sockets on either end.

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Leihcim
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« Reply #8 on: June 12, 2010, 01:22:12 PM »

Thanks for the advice on sticking the cables in deep enough in JTAG and plug. After double checking everyhting here for hours and scanning the forum on why I could not connect to the plug, pushing the cables in deeper was the solution!
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