Garbled serial line

Ben Leslie benno at
Sun Oct 26 03:01:53 CET 2008

On Sun, Oct 26, 2008 at 11:36 AM, Andy Green <andy at> wrote:
> Hash: SHA1
> Somebody in the thread at some point said:
> | 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.
> It's the kind of thing you'd see if the UART clock was slightly off on
> one end or the other, and your terminal software was replacing 0x80+
> with '?'.  In that case the funny characters would strictly follow the
> real traffic and never spew on their own or be totally missing.
> If you get unreal spews of rx characters, I would suspect the flat cable
> no longer making proper contact and floating the pins, mine lasted a few
> months before I had to pinch it by hand in the SMT connector at the
> phone and finally it died altogether.

Hi Andy,

Thanks for the info, very useful. On the first theory, would
underclocking the processor in u-boot (through the pll speed command),
help ? (Or give another data point?) I assume uboot adjusts the serial
timings when the plls are changed (?).  I think the real cause is
probably the latter, are you suggesting that the (cheap) cable is the
fail point or that the SMT connector in the (expensive) phone is the
problem? Assuming it is the cable, do you know if OpenMoko supplies
replacement cables?

Thanks a lot,


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