I'm not sure you and I have the same concept of "embedded." I have an 
O'Reilly book, "Designing Embedded Hardware," by John Catsoulis 2003 
(and a few more) so I'm still learning old stuff, you are adventuring 
into new stuff.

I just don't see Linux for embedded systems when Raspberry Pi etc. have 
miniaturized Linux so extensively. Perhaps my ancient neurophysiology 
blocks my thinking, but I see a hyperfast multitasking high storage 
system like Linux as the brain. And small specialized microcontrollers 
as dedicated peripherals linked via a central nervous system to the brain.

Right now all I'm doing is exploring serial port "nerve" connections to 
distant peripherals. The basic 3 wire connection of transmit, receive, 
ground certainly works well with simple terminal ASCII commands over the 
Atmel integrated UART. But further, DTR, RTS, DSR, CTS, DCD, RI are also 
available on the Linux driver as switched interrupt events that can wake 
a waiting process. That's a powerful connection at respectable speeds 
and proven line properties for multiple serial port device "nerve" 
channels to a Linux brain.

No doubt I2C, USB and what ever else might be great. My point with this 
post was how similar old DOS hardware access was to modern Atmel AVR 
assembly language ROM programming. A $5 MHz microcontroller is very 
interesting to a guy who spent many hours hacking steel on a Bridgeport 
mill with a caliper in hand. Robotics can have that job.

One interesting recent discovery is some RS232 line drivers/receivers 
now include chip enable/disable so addressable serial port buses are 
suggested (eg. Murata NM232DDC).

Perhaps the Linux "network server" concept is closer to a "robot server" 
than the robot itself.



Iznogoud wrote:
> Speaking of embedded, and in relation to what I had posted (asking for info on
> building an embedded system), I have done a lot of searching and found all the
> usual sources of info. It is not exactly what I am looking for, and the texts
> cited are scattered. One text that is almost mandatory reading is this O'Reily
> book: "Building Embedded Linux Systems - Yaghmour et al." The text does not
> read how I would write it, but it is good.
>
> I found that a lot of experimentation with VMs is excellent geeking out and a
> great practical learning tool. I think I'll get to what I want pretty quickly
> with some more individual effort.
>
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