Garbled serial line

Ben Leslie benno at
Sun Oct 26 01:06:54 CEST 2008

Hi all,

I'm hoping someone can help me out here. I have a GTA01, version B4,
with debug board version 3. I'm using the latest nightly version of
uboot. I'm having real trouble getting a console, u-boot or kernel, on
the serial console. I'm successfully using the JTAG, but the serial
justs echo '?' when I try to type.

The strange thing is it is almost working, for example, if I hold down
a key mostly it echos '?' but sometimes I get the actual character. On
occasion I've even seen the full uboot prompt.

My serial setting s are 115200,8n1 with flow control off. (Although
sometimes turning flow control on, and then off later results in some
characters getting through.)

I get the same behaviour regardless of the terminal emulator (although
the broken characters seem to crash iconv support in my version of
minicom, werid!). I've tried with different host OSes (mac and Linux),
different USB cables. I'm at a bit of a loss.

My best guesses are that there is something wrong with the ribbon
cable, although it looks fine, and jtag works, so it would just be one
line, not the whole thing that is broken if it is that.

My only other guess is that the tri-stating isn't working very well
(for some reason?) I thought it might be the old version of uboot
(somehow treating it as a B3 or something, which looking at the kernel
seems to have the tristate connect to a different pin), but I now have
the latest nightly, so it ain't that. Unfortunately I don't have the
tools or the skills to debug the actual hardware.

Can anyone make any suggestions as to what the problem might be, and
how I might go about debugging further?



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