[time-nuts] XRPU hardware on the current marketplace

[Bo Granlund]

Hal Murray kirjoitti:
>> Has anyone built this kind of device from something else than the VCC
>> HOT1 FPGA board? Is there some directly competing product that I
>> should know about, or something like that?
>>     
>
> I'm very interested in this area, but haven't actually done anything beyond 
> surf the web looking for something that fits my budget and interests.
>
> I think a major part of the problem is that bleeding edge silicon technology 
> as used by up-to-date FPGAs doesn't fit with 5V PCI.  (The specs call for 11V 
> spikes when the reflections are out to get you.)
>
> Most PCs have 5V PCI slots because most PCI add in cards are keyed for 5V 
> slots.  I haven't seen any motherboards with 3V only PCI slots, but maybe I'm 
> not looking in the right place.  In any case, I haven't seen any Xilinx 
> development boards setup for 3V only.
>   
I'm not entirely familiar with the power consumption characteristics of 
a FPGA, the ones I've dealt with have an power supply, and I haven't 
even cared to look at them more deeply to find out what they eat in 
essence. I'm not terribly experienced in the area of HDL 
implementations, or even using the system as sone kind of time source. 
I've found a company http://www.digilentinc.com/, that sells for a very 
decent price FPGA development boards. You get just about everything but 
the kitchen and sick with one of their products, for a very lucrative 
price, but I'm quite unsure howto connect the development board to a PC. 
They have somekind of bus architecture as far as I can tell, but I have 
no idea howto use it, my HDL skills are not that developed yet. And to 
interface with the PCI bus is maybe a little bit out of the scope of my 
personal knowledge, and the scope of this project I want to undertake. 
The board PHK used seemed to be ok, and I would be thrilled if I could 
aquire one of them, since they seemed to be quite ok for the task ahead. 
It's not a matter of building your own soft core, a counter for the 
frequency normal and a latch, and a interface to the PCI bus which can 
be memory mapped so that any processor can, and probably will fetch the 
time in a manner that doesn't require any kind of locking for the 
resource in kernel. If I understand correctly, this is exactly how 
FreeBSD does things, and there is even the, or rather, there was even 
the xrpu.c driver in the source code, as late as 7-STABLE, according to 
the cross reference setup by Robert Watson it seems as if they've 
removed it in 8-CURRENT, which is sad. I don't know about the way things 
are done in Linux land, and to be honest, I don't care. It's not that it 
wouldn't be a great operating system, it's simply that FreeBSD is much 
nicer.

> My straw man is to find an inexpensive board with FPGA and not much else that 
> will plug into a PCI slot.  I'm expecting to have to build a small daughter 
> card with a few coax connectors, level converters and whatever.
>
> Maybe the right answer is to wait until cheap PC motherboards have 
> PCI-express slots.  (Servers have already switched to PCI-Express.)
>
> The best I've found so far is a Spartan 3 on Raggedstone1 
>   http://www.enterpoint.co.uk/moelbryn/raggedstone1.html
> But the connectors don't have any ground pins and there aren't any mounting 
> holes.
>   
That seems very intresting, maybe it could be utilized to work for your 
application. What comes to daughterboards and such of your own design is 
rather scaring to me. I've done PCB design for something like a decade 
ago, and I didn't like it, it's just not my thing. But, if you ever do 
create an solution that I could etch myself and solder a bit of things 
on to the board, then why not, please do share your inventions with us. :-)

A Spartan-3 is perhaps a little bit too complicated for the particular 
project I'm looking at. If I'm to understand correctly, PHK did his 
thing on a much smaller FPGA. But I can't find the specifications of the 
HOT-I board anywhere. I kindof hope that some of the wizards comes 
around and enlightens us with his foresight.

I'm sorry for just babbling about things in general, but even a newbie 
has to start somewhere and learn the ropes.

warm regards, and have a happy new year,
Bo Granlund