On 21/07/18 16:00, Gene Heskett wrote:
On Saturday 21 July 2018 10:20:02 Mark Morgan Lloyd wrote:
I'd been comparing the performance of a Rockchip-based board's LAN and
USB against an RPi3B+, results were satisfactory. There's a modicum of
muttering that the 3B+ has broken something relating to the LAN or
USB.
I'm convinced its the internal usb2 hub that all i/o except the radio
and spi has to go thru. It has a rather annoying tendency to throw away
its own mouse and keyboard events. Thats not at all a pleasant
occurrance when the tossed event is a keyup, and it left 1500 lbs of
machinery moving with no stop except crashing into something. OTOH, once
code has been coaxed into a file, that file can run that same machinery
to do micron accurate work. The machine control is thru spi, writing 32
bit packets at 41 megabaud, and reading the responses 32 bits at a pop
at 25 megabaud.
The focus of people's ire ATM appears to be the RPi3B+, where the design
has changed the chip that implements LAN and USB hub functionality. Over
the last few days I've put a lot of time into this as the culmination of
a ridiculous amount of routing/firewalling testing, and while I'd quite
like to be able to accumulate more results what I can say so far is that
while a TinkerBoard can receive a data stream over 1GBit/sec Ethernet
and farm it out to at least three USB-connected 100MBit adapters before
performance starts degrading, an RPi3B+ can only handle one and when a
second is added performance is distributed unevenly... don't even dream
of adding a third.
The RPi range is good for what it was initially designed for, but that
LAN/USB chip appears to be its weakness. I've not sought out a datasheet
or worked my way through the kernel yet, but it looks as though there's
some sort of prioritisation in there that can get out of kilter.
Gene, is it one of these
https://www.pine64.org/?product=rock64-media-board-computer that you're
currently running to good effect?
Remainder noted with interest.
--
Mark Morgan Lloyd
markMLl .AT. telemetry.co .DOT. uk
[Opinions above are the author's, not those of his employers or colleagues]
