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Author Topic: semi-dead GuruPlug: not much jtag serial output  (Read 1491 times)
mookiedog
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« on: May 16, 2010, 03:59:37 PM »

I got a guruplug with JTAG box.  When I connect everything up and boot the device, I get no serial output as the device boots instead of all the marvbel/uboot text that should be scrolling by. 

The guruplug does boot though, because it does finally come up with 3 solid green leds and one blinking green LED.  At that point, if I type in 'root' and the default password 'nosoup4u', and then type 'reboot', the device reboots.  That means that the serial input is working. 

I checked the operation with 'local echo' on my terminal emulator program.  If I enable 'local echo', I get two copies of everything, as in:

rroooott
nnoossoouupp44uu
rreebboooott

(except that all the input is on the same line, meaning my <return> key is not generating a line feed)

If I disable local echo on my terminal emulator, I get:

root
nosoup4u
reboot

(also all on the same line)

The doubling of the chars I type must mean that the device is echoing the chars that I am typing over the jtag serial.

Any ideas why I do not get any of the other output over the serial?  Is there something I need to do after logging on the guruplug to fully enable serial IO?

Am I doing something stupid?  (wouldn't be the first time)
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two9er
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« Reply #1 on: May 16, 2010, 04:34:05 PM »

Recheck your terminal emulator settings: 115200 8N1, no flow control.
I suspect it my be the flow control.
Details here:
http://code.google.com/p/guruplug/downloads/detail?name=GuruPlug%20Server-Quick%20Start%20Guide-100507.pdf
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mookiedog
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« Reply #2 on: May 16, 2010, 04:53:26 PM »

I double-checked, and my flow control is disabled.

I do get some output from the guruplug: the echoing of what I type.  That is the *only* output I get though. 

The guruplug sees what I type and echoes it, but I never get any other output from the plug.  I can type 'echo "FOO!"', and although I see the chars echoed to my screen, I get no output from the 'echo' command after I hit return.  And like I said, I can type 'reboot', and the machine reboots so it is definitely seeing my input.

I have a sheevaplug, and the jtag serial IO mechanism works perfectly using all the same programs and same settings.
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mookiedog
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« Reply #3 on: May 16, 2010, 05:41:51 PM »

On a whim, I tried disconnecting the UART cable (the 4-wire cable) from the guruplug.  I still get the local echo, which seems a bit odd to me, but it means that the jtag box is generating the echo.  Obviously, I do not get any response to what I type with the UART cable unplugged.

So: This means that my guruplug is not generating any serial output at all, even though it is recognizing the input.

I ohmed the UART cable, and it seems OK.  So I think my guruplug must be defective, unless I am overlooking something.
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