Accounts on my bastion host for test farm access

[Hal Murray]

esr at thyrsus.com said:
> * an Anker 10-port powered USB hub, because Mark turned out to be
>   unsurpringly right that el cheapo unpowered hubs aren't stable
>   enough (ordered) 

I'm missing something.  What is that hub for?  Are you using it to power all 
the Pi-s?

USB provides 100 mA by default.  A device can ask for up to 500 mA.  It's 
supposed to ask/negotiate before it uses more than 100.  It's supposed to be 
able to ask while only using 100 mA.

If you have a 4 port hub, it can get 500 mA from the host, use up to 100 mA 
itself, and pass on 100 mA to each of the 4 downstream slots.

You can get tiny meters that plug into a USB chain to measure the current.  
Beware, they will reduce the voltage slightly, maybe enough to make a Pi 
unhappy.  My Pi 3 with HAT and GR-701W is taking 350 mA.  lsusb on the PC 
it's plugged into doesn't see any new USB devices so it didn't negotiate.

If I fill up 1 CPU with NTP requests, it takes 430 mA.

If I do a big memcpy, it takes 530 mA.

memcpy and NTP take 560 mA.

Without the 701W, it's only using 280 mA.  That's when idle.


-- 
These are my opinions.  I hate spam.