Re: USB "null modem" cables and related Linux driver questions
- Date: Fri, 1 Jun 2018 13:34:00 -0400
- From: Gene Heskett <gheskett@xxxxxxxxxxx>
- Subject: Re: USB "null modem" cables and related Linux driver questions
On Friday 01 June 2018 06:20:59 Richard Owlett wrote:
> On 05/31/2018 10:07 PM, Stefan Monnier wrote:
> >> I have two computers with USB ports.
> >> I wish them to communicate as simply as mid-20th-century computers
> >> did.
> > What kind of "communicate" do you need there?
> Essentially any ;/
> In fact one of the thought experiments I was pursuing was how to do
> file copying/sharing over RS232 - even I would not actually attempt to
Other than speed of the copy while the error correction verify's it
sector by sector, why not. Both rsync and rzsz are quite capable of
sending a file halfway around the planet with the last 17 miles on a
barbed wire fence. And getting identical crc's in the final check.
For a circuit that was actually that dirty, I think I'd choose rzsz as
its default packet size is 256 bytes. If the crc of that packet fails,
it requests a resend until it gets it right. So does rsync, but rsync's
default packet is 64k, demanding a far cleaner path. rzsz unforch has
several cousins 3x removed, so there is less than 100% compatibility.
And the linux version is one of the worse compatibility violators.
> > The "way back machine" to simulate a "null modem" serial cable
> > exists, as you've seen, but it's rarely the best solution for
> > nowadays's needs,
> "Best" is not an invariant absolute.
> > since nowadays connecting two computers is something completely
> > normal, supported by a deluge of tools, but they all expect a
> > "network" connection rather than a serial cable.
> > In most cases those two computers also have ethernet or wifi "ports"
> > so you can connect them via such a network (which usually offers
> > faster transmission than a serial cable, lets you seamlessly
> > multiplex several connections, and lets you use the many tools
> > working over the network to connect computers).
> An explicit requirement is a wired, NOT WiFi, connection.
> I that seriously. My internet access is a WiFi hotspot with its WiFi
> capability disabled.
> > In some cases one of the two computers's USB port is an "OTG" port,
> > meaning that it can act either as "master" or not, in which case you
> > can just use a regular USB cable (and usually you then configure the
> > OTG side to pretend it's a network card, so it ends up looking to
> > the software like you've connected the two machines via an ethernet
> > cable. That's what I use between my BananaPi "router" and my office
> > desktop).
> I saw it and it meets most (all?) my requirements except my reading
> 1. obsolete
> 2. available only for Windows/Mac
> 3. no way to determine if any of machines were equipped
> > If none of that are options, you can resort to using an "ethernet
> > dongle" on both sides and an ethernet cable between the two.
> That's a 1 versus 3 items required per connection.
> > All of those things will typically work "out of the box" on a
> > vanilla Linux kernel (the usbnet drivers have been incorporated
> > years ago).
> > Oh, and in case those computers are somewhat old, they may also come
> > with Firewire ports, and those (contrary to USB) don't have the
> > "slave/master" distinction so you can connect your computers this
> > way with a plain normal Firewire cable (and make it appear to the
> > software, again, as some kind of ethernet-like connection).
> > Stefan
Cheers, Gene Heskett
"There are four boxes to be used in defense of liberty:
soap, ballot, jury, and ammo. Please use in that order."
-Ed Howdershelt (Author)
Genes Web page <http://geneslinuxbox.net:6309/gene>