Date: Wed, 21 Sep 2005 02:38:11 -0500 (CDT)
Subject: moderate progress this evening
X-UID: 91
Content-Type: IMAGE/JPEG; NAME="img1842.jpg"

All of the gremlins have been chased out of my compact flash Linux 
distribution. It boots clean and does what I want. I had a small mystery 
yesterday with the dropbear sshd (Australian joke - nonexistent mammal - 
it is a bear that falls out of trees on prey). It was hanging on boot 
while generating RSA keys. Like other crypto applications, it relies on 
random number generation. Unfortunately, embedded systems often lack 
enough entropy for this. One solution is to use pseudorandom number 
generation which is of course cryptographically weaker. I'm not worried 
about it as this is a developmental system, not something that will ever 
be deployed in a production environment.

The motor control board is now wired for both SPI (Motorola invention) and 
I2C (what Atmel refers to as TWI, two wire interface, to avoid infringing 
on Philips trademark). The kernel patch I'm using for the GPIO pins was 
only done about two months ago. So it is too new and immature. The only 
sample code I've seen is for I2C. One advantage of SPI is that it is 
possible to reflash the microcontroller. So conceivably, I could remotely 
upload new firmware over the radio to the robot and reflash the 
microcontroller. I think this would be pretty risky.

Given how far behind I am and the difficulty I've encountered with this 
project, I've decided against safe modes. If a computer board resets, 
that's it. I may be able to login remotely and get things going again. But 
I'm not going to address the issues of redundancy, safe modes and security 
beyond what is easy to do. I don't expect to deal with hackers. One thing 
I might do though is strap a small ABC fire extinguisher on the robot. I'm 
not likely to remember to carry a fire extinguisher with me all the time. 
By having it on the robot, it will always be available in case of an 
electrical fire.

I'm not going to put the electronics back into the aluminum enclosure 
until I'm sure it works. I've learned my lesson from all of the missteps 
the past few weeks. Now that I have the DSO, there's no excuse not to 
check out everything. Also, I need to diagram the electronics. It's been 
maybe just two weeks since I've done anything with the motor control 
board. Looking at it tonight, it was challenging. I was intimidated. I 
didn't know where things were. It was one big mass of spaghetti. So I need 
to document everything while I still remember.