[time-nuts] clock-block any need ?

Bob Camp lists at rtty.us
Fri Dec 28 15:56:36 UTC 2012


Everything I've seen on the Adruino are "single chip wonders". They encapsulate the entire TCP/IP stack on the external chip. That will make getting at anything pretty tough. 


On Dec 28, 2012, at 10:21 AM, Jim Lux <jimlux at earthlink.net> wrote:

> On 12/27/12 11:48 AM, Attila Kinali wrote:
>> On Thu, 27 Dec 2012 11:30:37 -0800
>> Jim Lux <jimlux at earthlink.net> wrote:
>>> So, what about the USB-Ethernet dongles?  (I use them a lot at work to
>>> add a second interface for a laptop in test equipment setups, talking to
>>> a Prologix, for instance)
>> A lot worse! One thing is that USB has a polled protocol (ie the host
>> has to ask whether the device has any data) and the slot when an USB
>> device can signal that a packet came in repeates it self at most a couple
>> of times per 1ms frame for FS (don't know from the top of my head for HS).
>> The bigger issue though is that drivers for ethernet dongles are usally
>> of quite bad quality (ie it takes them a long time to do anything), and
>> they try to queue as much as possible to increase troughput (which adds
>> unpredictable delay).
> OK, so throw out the USB version..
> Just thinking out loud here: are these $20 wonders potentially a way to get "better" time transfer via Ethernet?
> I can see that a PC interface version might not be very good (because of the need to build a low jitter driver for the PC for SPI or RS232).
> But what about connected to some purpose built widget.. That is, rather than invest in a IEEE 1588 interface, could one cobble together something that does somewhere in between the vanilla mobo Ethernet & network driver that came with the OS on the "high jitter" end and some IEEE 1588 rev2 on the "low jitter" end.
> After all, there's no real "driver" when you're hooking it up to an Arduino.
> There might be some significant uncertainty in the microcontroller inside the interface chip: it does quite a lot.  But maybe not.. I haven't looked at it, and I was just curious.
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