[E3-hacking] Serial port oddity

Mr.G gtompsett at gmail.com
Tue Nov 29 23:11:47 GMT 2011

My development stopped at a controller for Christmas lights. I still have
two virgin units unopened in their boxes.

On 28 November 2011 12:12, David Given <dg at cowlark.com> wrote:

> I realise that the E3 is almost entirely irrelevant these days, but just
> in case anyone wants to get one working...
> I recently pulled mine out of storage and tried to put Debian on it. (I
> want to use it as a modem.) Unfortunately PBL wouldn't handshake.
> Investigation showed that at baud rates of 57600 and above, the E3's
> serial port seemed to be unable to receive data reliably, getting
> frequent single-bit errors. Transmission seems fine.
> I eventually managed to get everything working by dropping the baud rate
> to 38400 (uploading the kernel and initrd takes an *age* at that speed),
> and everything works now.
> This might be age-related; my E3 is now years old. A flaky capacitor
> causing the pulses to get smeared so that the UART isn't registering
> them properly? This seems particularly likely given that I don't have a
> level shifter, so I'm driving the UART at out-of-spec voltages.
> Alternatively it could be clock drift, but given that the UART is on the
> processor this seems unlikely.
> So if anyone has an E3 which won't handshake any more, try lowering the
> baud rate and seeing if that helps. (pblq has an option for this.)
> ...
> Incidentally, I don't suppose any of the uboot patches got accepted by
> upstream, did they? Editing the environment with a hex editor is
> slightly harrowing and it'd be so nice to have a version which could
> store them in NAND...
> --
> ┌─── dg@cowlark.com ───── http://www.cowlark.com ─────
> │ "I have always wished for my computer to be as easy to use as my
> │ telephone; my wish has come true because I can no longer figure out
> │ how to use my telephone." --- Bjarne Stroustrup
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> e3-hacking at earth.li
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Best wishes

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