daddylonglegs

Useful systems have huge positive externalities that can't be captured by charging passengers at a rate that reflects those benefits (I'm not sure if this is due to a free-loader effect, irrationality on the passengers part or something else).

I think the only systems that have profited on scale commensurate with their benefits are those that were a real estate play, eg.: the Metropolitan Line[1] in London, Los Angeles trams, Hong Kong subways. I might be wrong about these examples, either due to misremembering or to falling to a just-so story.

I think the XC7A100T is supported by the free (and limited) edition of Vivado [1]. Of course, the confusion about what you can and can't do with the HDL is in itself a barrier to open source and hobby work. This is true even when the work is theoretically possible and everyone has the best of intentions. <sigh>

However, I think they've used code from NetTimeLogic under a licence [1][2] that precludes distributing the source:

> 3.2 Distribution Rights. LICENSEE may reproduce and distribute the Licensed Materials, solely in binary form that operates in LICENSEE’s system-level hardware products.

This is a perfectly reasonable way of developing a system but it is sadly incompatible with sharing your work as open source.

I've seen plenty of projects described as open source when the firmware is open source and the hardware is closed but this is the first time I've seen one where the schematics and board layout are open but the firmware is closed. Note that the hardware itself is quite simple, the smart stuff happens in three modules: GNSS receiver, precision clock and FPGA. To me, the contents of the FPGA source code are the only interesting part of this project. Additionally, you won't be able to meaningfully modify or reuse this project without editing the source code.

The hardware module these FPGA binaries seem to be compiled for is described as an AC7100B, the source given for these is a defunct ebay link [3] [4] :-O This project uses two and half grand's worth of atomic clock and the heart of it runs on a module that fell off the back of a lorry!?

I don't think this is right. GPS explicitly uses a timebase that does not include leap seconds [1].

On the subject of the article: my modest and very reasonable proposal is that we apply a leap second every six months without fail, dithering between positive and negative leap seconds so as to remain close to sidereal time. That way we would flush out bugs every six months and wouldn't have them accumulate and hit us all at once.

Or we could be boring and use TAI or GPS time as the system clock every where and apply leap second corrections when we go from the system clock (currently UTC) to local time.