Re: A10-OLinuXino-LIME board
On Mon, Aug 25, 2014 at 1:22 PM, Karsten Merker <merker@debian.org> wrote:
> On Mon, Aug 25, 2014 at 01:46:50AM -0700, Joey Hess wrote:
>> Ian Campbell wrote:
>> > Why hd-media? The standard netboot images work fine on sunxi AFAIK
>> > (testing on cubie{truck,board}).
>>
>> Board doesn't netboot by default AFAIK, so this would need a serial
>> console, which needs a nonstandard cable.
>
> Hello,
>
> I have just looked at the board manual at
> https://www.olimex.com/Products/OLinuXino/A10/A10-OLinuXino-LIME/resources/A10-OLinuXino-LIME_manual.pdf
> and found the the description of the serial port rather
> confusing.
it's fairly standard nowadays to put a UART over pins that are
shared/multiplexed with other functions such as GPIO. in order to
avoid having to do "special I/O drivers" on the SoC they simply put
the 0s and 1s effectively straight out of the same pins at the same
voltage and current levels as the GPIO that they multiplex/share.
otherwise it would be necessary to have special RS232 driver logic
on-board the SoC and if you know how big I/O driver pads are compared
to actual transistors for logic or memory you start to appreciate why
this is almost never done.
so this is why you need a converter IC. it's actually very very
common practice, and things like the FTDI chipsets or the MAX232 will
do the job perfectly... for a given level of perfect. the only thing
you have to watch out for is not to spike the SoC or the USB
converter, especially when powering up from a separate power supply
from the USB converter you're connecting to.
typically FT5306s and MAX232s will easily support the full range 3.3
up to 5.0v input signal levels of SoCs so you need not be concerned
about having voltage converters: just wire them directly up...
preferably just *after* powering up.
there are people with a little more experience at this sort of thing,
henrik (u-boot maintainer) is one such person i know who can give you
a much better idea of the full technical details and the gotchas.
but, basically, grab yourself something like an FTDI USB dongle off
of farnell and you should be set. something like this:
http://uk.farnell.com/ftdi/um232r/dev-module-usb-to-serial-uart/dp/1146036?Ntt=FT232+USB+UART
l.
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