[Cryptech Tech] Alpha layout done (not a joke)

[Jacob]

On 4/1/2016 10:28 PM, Pavel Shatov wrote:
> On 01.04.2016 19:57, Jacob wrote:
>>
>> What's the purpose of J2/J3?
>>
>> Jacob
>>
>
> Sorry, forgot to answer this one.
>
> We currently have two USB-to-UART transceivers by FTDI onboard. There
> was a heated discussion on the list (FTDI is notorious for their driver
> issues, etc), I'm not going to reproduce all the details, but it all
> boiled down to the fact, that we eventually decided to try replacing
> them with some small general-purpose USB-capable ARM processor.
>
> We decided to add these headers, so that this custom transceiver could
> be designed independently. They will enable us to unsolder the FTDIs and
> test the transceiver with Alpha board. If it works out with Alpha, we'll
> use it for Alpha2 or Beta board instead of FTDIs.

So if those headers are for a dev option and not for the end-user, I'd 
recommend to change them to 0 Ohm resistors (preferably 0402 or, if you 
wish for ease of "basement soldering", 0603).
The reason is that USB signalling requires special care - differential 
routing with controlled impedance and away from other noisy lines - and 
the big header pads break that path.
If you leave it as it is now, the USB interface will still work, albeit 
at reduced speed due to re-negotiation of lost packets.