Oh, boy, did I stir up a hornet's nest.
My open letter generated some serious anger responses. I won't take those public, and I hope the authors won't either, because it is counterproductive to do that stuff.
Some things have been mentioned, though, that are substantive in nature.
In a private discussion, Dan Sexton, from GE, one of the Committee Chairs of SP100, suggested to me that while he was initially in favor of testing, he's thought better of it, primarily because of two reasons: first, it would, in his opinion, delay the standard unduly; and second, because he isn't sure that we'd learn anything substantive at this point from testing.
Dan's points are both valid and arguable.
However, I think that some consideration should be given to the following:
1. The standard itself is larger and more complex than the PHY layer, and work on the rest of the standard should not be delayed by testing. If we structured the testing in parallel with the rest of the work on the whole standard, I am not sure we'd be introducing any substantive delay.
2. I am not sure that Dan is right about not learning anything new. I suspect that's a matter for discussion by the committee. We certainly could discuss the implementation of the IEEE compatibility and coexistence model, and whether we could use that procedure as our own testing modality.
Pat Kinney, also one of the committee chairs, brought up a point in a private email that made me stop and think...he suggested that the standard could require a chipset with a dual PHY, such as 802.11x has done.
That actually sounds quite reasonable. If it is practical, it is a way out of our dilemma.
Here's where the rubber hits the road, however. I am seriously in doubt as to whether the economies of scale can produce a piece of highly customized silicon cheaply enough to permit S100 equipment to be made at a reasonable cost.
I'd like to hear from somebody with a silicon foundry on this point.
The other issue on which I have questions regarding a dual PHY on a single chipset is that it was my understanding that a frequency hopping system is not capable of coexistence with an 802.15.4 system on the same chip. Here again, this is outside my area of expertise. Where I've instrumented many silicon foundries I've never run one, and never designed a chip...so it would be nice if somebody stepped up and answered this one for me.
Here's the bottom line, friends. The end user community that is the target market for S100 hardware is exceptionally risk-averse. And they OUGHT to be! They aren't going to implement anything and see if it works...they are going to wait until somebody else does it.
Unless we can give them a standardized PHY so that they can pull ANY manufacturer's device out of the box and have it start up and run, and we can show them data that proves that there is a significantly less than 0.0001% chance of interference and problems with coexistence, THEY AREN'T GOING TO BUY IN DROVES...JUST LIKE THEY HAVEN'T BOUGHT ANY FIELDBUS BUT HART IN DROVES FOR THE LAST TEN YEARS.
I want to go on record that I'm not carrying water for any supplier here. I am speaking as the voice of the end user community. I cannot imagine any other outcome of a multiple, incompatible PHY than rejection of the standard by end users voting with their feet.
Now, look at this.
At least 12 vendors (okay so I am letting the cat out of the bag a couple of days early) will be displaying working and interoperable HART Wireless prototypes in the HART booth at ISA on Tuesday, Wednesday and Thursday. Included in this list are Yokogawa, MACtec, Honeywell and Emerson, and eight more vendors.
Here's a hard question for you:
If those people can produce a common PHY for HART wireless and bring it to market in a reasonable time, what is to keep SP100 from doing the same thing?
As far as my suggestion that ISA take a hand in at least funding the testing is concerned, things have radically changed since my open letter.
ISA's announcement yesterday that they had established a compliance testing arm indicates that ISA and the Standards and Practices Board are intervening in the compliance testing arena for after-issue standards compliance testing.
It can't be much of a stretch for us to suggest to ISA that this new entity also be in charge of pre-issue standards testing, such as I have advocated. The arguments made recently that ISA has never done testing and shouldn't be doing testing are pretty much swept away.
And we needn't wait for ISA to staff up this new entity either. We have the ability to use existing members of SP100, as I said in my open letter, such as ORNL, INL and Sandia Laboratories, to contract the testing work necessary.
So, fellow members of SP100, think about these things as you prepare for next week.
Walt
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