Which embedded system would you use?

On 2011-05-17, linnix <me@linnix.info-for.us> wrote:
> On May 17, 4:32&#4294967295;pm, "Sink0" <sink00@n_o_s_p_a_m.gmail.com> wrote:
>> The reason to use fiber would be noise imunity. But a shilded twisted pair
>> for now is ok for now. But i could not get.. You say to use a hub for node
>> groups.. but they are aligned.. imagin an pearson's arm and nodes
>> distribuited over the arm. So if we use a hub... there are on cable from
>> each nod going to the hub.. thats a lot.. and finally.. you told me it is
>> possible to send 64B with a 20us time with USB. That would be ok if i could
>> address many nodes with one message. But 20us for each node for the request
>> and answer would be something like 120us of lattency for 3 nodes on a
>> channel for data transmission. WHat is the reliability on this number? And
>> are you including the Linux response time?
>
> No, just raw USB data transfer.
>
> 12,000,000 bits per sec
>= 4,000,000 bytes per sec
>= 80 bytes per 20 uSec
>
> But USB frames are limited to 64 bytes, perhaps a little bit less.

What is the minimum USB polling interval these days ?

In the UHCI days, it used to be 1ms, then it dropped to 125us for USB 2.0.

Since people here are talking about 20us been achievable, it's obviously
dropped further but a quick search online only found the EHCI era 125us
specs.

Simon.

-- 
Simon Clubley, clubley@remove_me.eisner.decus.org-Earth.UFP
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