gEDA-user: update on furnace board

[DJ Delorie <dj@xxxxxxxxxxx>]

I've been working my way through the subsystems, testing everything
and writing software as I go.  So far, pretty much everything works as
designed, with only a few minor ECOs.  Most of the changes are tweaks
to resistor values to adjust edge times and LED brightness.  The only
design "flaw" so far is that one of the comparators I'm using is open
collector, and I thought it was push-pull (the other one *is*
push-pull), so I need to add some pullup resistors.  (yes, Dan, I'll
be using that grid of pads you suggested ;)

As an amusing aside, the five MCUs have serial consoles :-)

The gumstix talks to the MCUs using i2c.  However, the in circuit
programming using some GPIOs and a multiplexed serial port.  So, I can
have the programmer (which runs on the gumstix) stay connected to the
serial port after programming, and the MCU can print to it.  I can
only monitor one at a time, but it's handy to have printf() when
debugging.

I'll probably add pull-ups to the /RESET lines on the MCUs so they can
run without the gumstix even present.  I imagine one could write a
functional furnace controller just using the five MCUs talking to each
other over i2c (the R8Cs can be i2c masters or slaves), as the R8C-26
has 32k of flash and 1.5k of ram, enough to run a supervisor (the four
R8C-1Bs have 16k of flash and 1k of ram).


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