I fully agree that ASIC is the long-term way to go, but this UART token ring thing seems to be rubbish to me. There are well-suited protocols for this, like for example I²C.
There are two possibilities:
- Build a PCIe mining accelerator card, with some PCIe to I²C (or whatever) bridge, possibly on a CPLD.
- Slap an ARM SoC and an ethernet adapter on the board as well and make it run autonomously.
Let's say each manufactured chip would yield 100 MHash/s. We daisy chain 20 per boards (a board with 20 chips on it is not a big deal) That's 2 GHash/s right there. PCB design and manufacturing would be pretty straight forward. I volunteer for that.
Good to know, as I have never dealt with this area before. Could you provide an estimate for the non-ASIC cost? (PCB design, prototyping, manufacturing and assembly, voltage regulators, clock generation, ...)
Assuming a 4"x6" board 4-layer board, the PCB itself would cost about 25$ a piece in low volume (100 pieces...that's from pcbexpress.com). If there's not too much routing, we could go for a 2-layer board which would be half the price. Cut that in half if we make 1000's.
Assuming there is less than 100 parts on the board, assembly of 100 boards is about 50$ per board (that's from aapcb.com). I usually assemble the first prototype(s) myself. Again, cut that in half if we make 1000's.
We really need to wait how the ASIC shapes up before making wild guesses on the required additional components on the board (regulators, oscillator, interface, etc.). However, I would be really surprise if this turns out to be more than 10-20$ per board depending how "stand-alone" is the board.
PCB design is free, I have all the tools.