random stuff serial usbboot and booting off sd card

Bas Wijnen wijnen at debian.org
Sat Dec 5 10:42:33 EST 2009


Hi,

On Sat, Dec 05, 2009 at 02:37:35PM +0100, Kristoffer Ericson wrote:
> Ive just purchased the tools needed to wire together the serial
> adapter. Anyone done this before and can offer some good advice?

Most of the ICs which do the voltage conversion need external power.  If
you want to experiment with USB booting anyway, you can copy my setup
(but you may not want to experiment, see below):

I have a board which connects a USB B recepticle (the plug in a printer,
for example) to a USB A recepticle (the plug in a computer).  No logic
is there, but all four wires are made available with 4mm plugs.  For the
current plan, you only need the black and red wire (the power lines).

Then I have another board, which has a max232 on it with the required
five capacitors to make it work.  Its rs232 in/outputs are connected to a
standard 9 pins serial port connector; its ttl in/outputs and power
input are made available using 4mm plugs.

Finally, I have soldered the TxD and Gnd pins of the NanoNote to wires
which also end in 4mm plugs.  I don't need the RxD, but it's trivial to
add it as well.

Having all this, I connect the following:
- NanoNote ground to max232 ground to USB ground.
- NanoNote TxD to max232 data input.  You should connect the RxD to the
  data output as well, if you want it.
- max232 Vcc to USB vcc so that it gets powered.
- computer USB port -> USB board -> nanonote with two USB cables.
- max232 serial connector to the computer's serial port.

To make this clear, I made a photo of the whole setup.  You can see it
on http://pcbcn10.phys.rug.nl/~shevek/nanonote-serial.jpg .

> I was also planning to fix the usbboot so I can more easily reflash
> when needed.

If you're planning on running Linux, this may not be a good idea.  When
the pins are connected, the device cannot boot normally.  It will wait
for commands from the USB host.  For Iris, I send it the kernel and run
it.  That should be possible for Linux as well.  However, nobody is
currently doing it. ;-)  The normal procedure is to use USB boot to
reflash, then test using normal boot.  So fixing them together isn't a
good idea unless you want to experiment with booting the device
"normally" over USB (which shouldn't be really hard, AFAICS, but it does
require some work).

> Those pins seem extremely close to one another so might be near to
> impossible to get it perfect without risking permantently merging them
> (which would be bad!).

The man who makes no mistakes usually doesn't do much else either. ;-)

I have soldered the pins together, and it wasn't a problem really.  Just
make sure you have 0.5mm solder wire, not the thick one of 1mm.  I've
also unsoldered them twice now, to test some things, and resoldered them
after that.  No problems at all.

> Ive also gotten hold of micro sd so will use that to test the userland
> instead of flashing.

If you want to do that, you will not want to fix the usbboot pins
together, because if you do, you can only boot from USB.

Thanks,
Bas
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