Computing stuff tied to the physical world

Tiny embedded Linux

In Hardware on Mar 8, 2009 at 00:01

The MMnet1001 is an interesting little setup, based on the AT91 ARM chip. Here’s a close-up image, as provided by Propox:


The ethernet connector is about the only hint you get on how small this thing actually is. It’s shorter than a JeeNode (and it has a lot more hardware!).

I did not order the development board with this, given that I only need minimal hardware interfacing. So my first try was to simply hook up 3.3V power to J2-1 and J2-2 and plug in an Ethernet cable.

Hmm, nothing happens. No new device shows up on the LAN. It turns out that the bootstrap uses a debug serial line, and unfortunately in this revision the internal pull-up on the RX pin is not enabled. So the bootstrap picks up something on the line, and then waits for a complete command.

A 10 KΩ pull-up resistor on J1-13 fixes it. The user LED is flashing!

Now I can see a network device, but it won’t let me in via SSH and I don’t see an HTTPD server on port 80 either.

Ok, time to hook up the serial port @ 115200 baud via an FTDI cable. Aha!

Picture 3.png

(actually, this is the text I get after editing out some cruft from “/etc/issue”, not a first-time hookup)

Great. I’m in. And there’s a “dropbear” SSH. Ok, turns out the root password hasn’t been set – that’s easy to fix.

Yes! Now I can connect over ethernet at last:

Picture 5.png

Perfect. The serial line is no longer needed. This thing now boots up and lets me in via SSH without further tweaking.

Power consumption @ 3.3V is about 250 mA idle and 350 mA when running the CPU at full load. Here are some more system specs:

Picture 6.png

All is well. Onwards!