[SGVLUG] The tangential flogging continues (was: bit order (was Linux based web-server appliance))

[Jeff Keys]

On 5/24/06, TOM EMERSOM <Tom.Emerson at wbconsultant.com> wrote:
>
> But, in the ever obscure way in which google returns search results,
> this page was a good trip down memory lane...
>
> http://wwwcsif.cs.ucdavis.edu/~csclub/museum/cpu.html
>
> [and now I'm late for an appointment...]
>
>

I have a small quibble with the above-mentioned site,
http://wwwcsif.cs.ucdavis.edu/~csclub/museum/cpu.html, where it says,

    "The RCA 1802 was an odd beast, extremely simple and fabricated in
CMOS, which allowed it to run at 6.4 MHz (at 10V, but very fast for
1974) or suspended with the clock stopped. It was an 8 bit processor,
with 16 bit addressing, ...

... Apart from the COSMAC microcomputer kit, the 1802 saw action in
some video games from RCA and Radio Shack, and the chip is the heart
of the Voyager, Viking and Galileo probes. One reason for this is that
the
1802 was also fabricated mounted on sapphire, which leads to radiation
and static resistance, ideal for space operation."

Galileo's Command Data System had 6 1802s, and of the 19 total
microprocessors onboard, I think 17 of them were 1802s, one running
code written in Forth. Viking and Voyager have no 1802s; rather the
Command Computer System was a hand-wired 18 bit machine with no
operating system and about 4K memory. How handy it was to be able to
write FORTRAN arrays packing 18 bit CCS code on the Univac's 36 bit
architecture...

Interestingly, Google turns up a number of sites claiming that Viking
and Voyager had 1802s, some claiming they ran at 6.4MHz, the number
mentioned by the above author, though he is saying the 1802 can do it,
not that the spacecraft implementation did. A Wikipedia article,

   http://en.wikipedia.org/wiki/Galileo_spacecraft
says in part,

"The spacecraft was controlled by a RCA 1802 Cosmac microprocessor
CPU, clocked at about 1.6 MHz, and fabricated on sapphire (Silicon on
Sapphire) which is a radiation-and static-hardened material ideal for
spacecraft operation. This microprocessor was the first low-power CMOS
processor chip, quite on a par with the 8-bit 6502 that was being
built into the Apple II desktop computer at that time. Galileo's
attitude control system software was written in the HAL/S programming
language, also used in the Space Shuttle program. The 1802 CPU had
previously been used onboard the Voyager and Viking spacecraft."


I have to wonder where these numbers came from. I remember them being
a bit slower, maybe 200 KHz for the 1802s in the Galileo CDS, the
Voyager CCS was faster, if my memory is any good.

Another correction: that paragraph sort of implies that the attitude
control system was an 1802. Not so; it was an ATAC built from four
rad-hardened 4 bit Itek 2901s. It had an RTOS and an FPU, and ended up
being the only subsystem on Galileo written in HAL/S in spite of a
project policy early on that all flight and ground software would be
written in HAL/S. The AACS guys liked it for its matrix functions;
everyone else found technical reasons not to use it, such as no
adequate compiler available.

Jeff