How hard is to build a processor?

TTman wrote:

>

... and there's the rub! :>
I designed a processor some years ago. A friend was responsible for writing the code for it.
*Nothing* worked! :< This was completely unexpected as we were both very competent in our individual responsibilities.
We soon realized that I had designed the instruction set expecting "word" addresses (memory was 16b wide and only accessible *as* 16-bit words -- hence it seemed *obvious* that addresses would be of "words") whereas he had assumed *byte* addresses. :< Simple fix. Took all of the drama out of the event! ;-)
I've seen other silly issues like this confound the initial startup of custom processors: e.g., confusion over which way the stack grows, whether the SP points to the last *used* location on the stack or the next *available*, etc. They are almost always "fun" problems to solve as they usually are easy to find and have dramatic consequences once found!
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Don McKenzie wrote:

In the early 80's it was common to build "custom" processors out of 2900 bit-slice components. There was an excellent text (and some good AMD appnotes) devoted entirely to this (Mick 'n' Brick? yellow dust jacket).
In grade school, I build a combination (burglar) alarm using (bistable?) inter-latching relays for the code store. With a fire department klaxon as the annunciator (you *really* didn't want to get the combination wrong! :> )
In high school, I built a two-player (offense + defense) football (left-pondian football, that is :> ) game out of analog computers (integrators, adders), DTL and VOM's (to display: "down", field position, yards gained/lost on the play and yards 'til first down) but that just ran at "DC". It was also quite large (4' x 8' sheet of plywood to hold all the bits) and, thus, impractical to preserve.
Many years ago, I built a "digital clock" out of relays. But, it was very noisey and cost a fortune to keep replacing the incandescent lamps used in the "7 segment" displays.
Now, I am much more fascinated by electro-mechanical *mechanisms*. I have been working on a kinetic "sculpture" to act as a timepiece in the back yard. A tribute to Rube Goldberg -- with the exception that it must run *continuously* (most of his contraptions were "one-shot" devices). But, in order to keep *good* time, I need to "close the loop". Doing so without being noticed means using some "non-discrete" device that you can control. I.e., something like a liquid whose rate of flow can be varied without a critical observer being able to *easily* determine that this is happening. Living in the DSw poses a problem using water as it evaporates too fast (replenishing it from the domestic water supply would be "cheating" :< ). I also need to locate some larger solar panels so the device has no connection to the electric utility.
I would also like to build a "Jetson's" style doorbell (though programmable) to replace the electronic version I made some years ago. But, apparently, the design of tubular bells is more art than science (and, mistakes can be costly). So, I have a lot more research to do. :<
"Toys" <grin>
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Yes, Mick and Brick. An absolutely outstanding book on datapaths. and microprogramming; it was all based on 2900-series, but the concepts mapped to everything.
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Yup! I read Mick and Brick cover to cover and learned a lot from it. I never built anything with bit slice other than on paper. But I have a lot of respect for those who did. I even used a "high end" workstation once that was a suped up 68000 made out of bit slice. I think it had a marketing window of 15 minutes before Moto came out with a 680xx or something much faster than the 68000.

I have thought about how to make a time piece that is actually regulated by the flow of water. It would be hard to get this to be accurate, but I havae some ideas on how to make it fairly good. I am in the mid-east US, so we normally have lots of rain. I have thought about ways to make it "self-winding". One is to simply catch rain from the roof and keep the top reservoir full. Another would be to use wind power to pump water from the lower reservoir to the top. That would be doubly cool. It might even allow the clock hands to be in front of the windmill blades!
But this project is way off in the distance. I have many other things to do first.
Rick
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The clock/calendar I hope to build over the next year or so will be solar. The shadow of a post uniquely determines both date and time, if you look at both angle and length....
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Hi Joe,
Joe Pfeiffer wrote:

Hmmm... is that (really) true? Or, don't you end up with *two* date,times for each angle,length? E.g., won't the angle,length be the same for HH:MM on the day before and after the Summer Solstice? Or, close enough to make it near impossible to differentiate? (dunno, I find thinking in 3D on astronomical scales difficult :> )
Like me, at least you'll have plenty of Sun to play with! (NM)
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Yes, I should have said "just about unique." I wouldn't be at all surprised to find out the variation with date won't be possible to distinguish more accurately than a couple of days, too.

I like living down here!
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I'm not sure where I got this image in my mind, but I seem to recall that the motion of the end of the shadow at a given time each day moves in a figure eight over the course of the year. Ok, I got over my laziness and googled it. This is called the "analemma" and is caused by the tilt of the Earth's axis and the elliptical orbit around the sun. This still does not make the position at all times and days unique, but it does help a bit (and hurt since it becomes a lot more complex to label).
Rick
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On Fri, 26 Feb 2010 23:06:50 -0700, D Yuniskis

The elevation of the sun varies very little close to the solstice, about the solar diameter (0.5 degrees) at +/-8 days from solstice and only about 12 arc secs at +/- 1 day from the solstice.
Various tropospheric refractions can alter the apparent elevation. The refraction is worst close to horizon, so the winter solstice will be worse. Trying to determine sunrise and sun set times is even worse, since average refraction is just slightly less than one degree and can vary quite a bit from day to day (even mirages).
The solar elevation changes rapidly close to the equinoxes (about the solar diameter/day), so this is the best time to determine the date.
Determining the local solar time is easy, just determine when the sun transmits the meridian (i.e is directly in the South in Northern hemisphere). Some local clocks are required to divide the time until the next solar transit into 24 hours. The time between two transits is not usually 86400 (atomic) seconds, but varies slightly according to the equation of time (which is due to the elliptical orbit of the Earth).
Averaging these variation over the year, you can calculate the mean solar time, in which the day is exactly 86400 seconds long.
Waiting for a year to determine the mean solar time or using a sufficient accurate local frequency standard, you can determine, if the actual solar day is longer or shorter than 24 hours, which may help some ambiguity problems in the elevation measurements. Determining the date is much harder due to the refractions, but averaging over a sufficient number of measurements (days), this should give relative accurate results at the equinoxes.
Once you know the mean solar time and know your longitude, you know the time at the zone meridian (0, 15, 30, 45 ... degrees E/W). Knowing your latitude, you can determine in which country you are in and hence which time zone is actually used at that area. Finally by knowing your date, will allow you to calculate, if daylight saving time should be used :-).
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yes.
that may happen for some dates of some years :)
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Actually, it happens for every day of every year other than the solstices. The two solstices (actually a day or two on either side depending of the season) has the lowest or highest path across the sky, so no other day will have quite in that same path. But every time of every other day (excluding a few seconds at the start and end of the day when one day has sunshine and the other does not) will match a time of two days, between spring to fall and one between fall to spring. The path of the sun may not be the same on those two days, but each point will map to two different times and days.
Rick
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rickman wrote:

So (thinking in terms of a *truly* unique hack), if you *watched* the motion over the course of a particular day (e.g., 'yesterday'), could you *uniquely* determine that day?
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Given lattitude and longitude (or equivalent) and sufficiently good instruments, and the right data and skills, yes.
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Jasen Betts wrote:

So, a *device* that watched these things could deduce date/time (?) How much more would it have to do to deduce location (or, at least, latitude)? Probably just watch for a longer period of time?
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I can't say this for certain, but I believe the combination of length of day and elevation of the sun at the zenith is a unique combination for each day of the year and latitude. So I think you can get your latitude the same day. But I'm not sure you don't have the same two day ambiguity. Otherwise I think the combination is unique. Even the North-South issue can be resolved because of the eccentricity of the Earth's orbit making things a little different in the two hemispheres. But you may also be foiled beyond the artic/anartic circles where the sun never sets. Then you only get one parameter, the elevation at the zenith. But you might be able to make up for that by measuring the time between the sun at due east and due west... other than at the poles where there is no east or west... ;^)
Rick
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rickman wrote:

It is close but not exact. The earth's orbit is not an exact number of days. For the calendar's purpose we accumulate errors and adjust the calendar. These adjustments are every 4 years and sometimes on the century. There are other errors that have an impact on the observations depending on the required accuracy.
I saw a sundial on a beach near Kobe Japan that had elaborate error correcting instructions that was probably good to a second after ten minutes of calculations. There were a lot of factors involved it accounted for earths orbital period

Above the arctic circle the sun 24 hour path is tilted but there are other factors that are significant. For a couple weeks around June 21 the sun never sets as far as 80 miles or so south of the arctic circle. Most of this is due to the optic effects of the atmosphere. Even above the arctic circle actual and observed position of the sun has significant differences.
Regards,
w.. -- Walter Banks Byte Craft Limited http://www.bytecraft.com
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Hi Walter,
Walter Banks wrote:

I always thought a cool hack would be a motorized sundial. (i.e., the motorization being a cleverly hidden aspect) E.g., with nice, evenly spaced markings -- and a motor to rotate the whole assembly such that the shadow fell "where it should" (on this nicely marked indicator).
It;s the sort of thing that would elicit comment *only* from someone who *knew* it was "quite impossible" to work as it *suggests* it works...
(obviously, I like things that mess with people's heads :> )
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The fish-hook here is in the careful wording of "and sufficiently good instruments, and the right data and skills, yes"
So a smarter question, could be what is practical ? - and using what measurement systems ?
I found this revealing page, which has real datapoints, and a practical location (ie less than ideal)
http://www.austintek.com/astro/analemma/analemma.html
Most revealing are the nice dots-on-the-door
http://www.austintek.com/astro/analemma/images/4215.door_from_inside_rotate.jpg
and the red arcs, are snapshots of the actual path, ~4wks - note they include a dot on alternating sides of the analemma, as the 12 arcs interlace.
This site below shows the analemma actually moves yr-yr, so that's more data to track ;)
http://myweb.tiscali.co.uk/moonkmft/Articles/EquationOfTime.html
-jg
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On Tue, 09 Mar 2010 10:20:08 -0700, D Yuniskis

By observing when the sum passes the meridian, one cloud free week in the spring and one in the autumn should give a quite good resolution for the latitude, provided that some internal time reference is capable of measuring the number of days between the measuring periods with at least +/-12 hour accuracy. During one week long period the sun moves south and on he other it moves north.
Of course, there is the north/south hemisphere ambiguity, but with additional sensors to the left and right of the meridian line should help solve this ambiguity. After all, in order to detect meridian passing you would have to align the device towards true north.
A camera with at least 150 degree field of view pointing directly upwards towards zenith, should be able to detect the orientation, latitude, date and local solar time within a year of observations.
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The hardware for this is in the current issue of Circuit Cellar. Different programming needed....
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