It's not QUITE this bad but it is pretty bad.
I use USB external hard disk docs and disks for backup. Once you get a
COMPATIBLE device then backup over USB is reliable.
But there are many dock models out there that won't work with different
motherboards or will work a few times then stop working.
And it's the same thing whether you are running Linux or Windows on the systems.
I have also tried using USB-to-serial dongles for industrial control of PLCs
and such, it did not work. The dongles will drop characters and the market is
full of counterfeit dongles anyway. The rs232 port pcie cards generally work.
Ted
-----Original Message-----
From: PLUG <plug-boun...@lists.pdxlinux.org> On Behalf Of Ben Koenig
Sent: Friday, October 27, 2023 12:46 PM
To: Portland Linux/Unix Group <plug@lists.pdxlinux.org>
Subject: Re: [PLUG] Simultaneously horrifying and amazing!
------- Original Message -------
On Friday, October 27th, 2023 at 10:20 AM, Bill Barry <b...@billbarry.org>
wrote:
> On Fri, Oct 27, 2023 at 12:15 PM Russell Senior
> russ...@personaltelco.net
>
> wrote:
>
> > It wasn't the RS-232 that surprised me, it was the combination of
> > RS-232 and PCI-E, when I expected that modern RS-232 interfaces to
> > just use a USB converter. It is kind of like finding someone putting
> > a Pratt and Whitney turbo fan on a Sopwith Camel.
> >
> > And here I was just about to reply and ask what would be the
> > advantage of
>
> a PCI-E card over the much cheaper USB converters :)
>
> Bill
USB is designed as a user-friendly Plug 'n Play connection. There is a lot of
variety in how it is implemented and it tends to do weird things when used for
long term connectivity.
I encountered this in the storage world. People who use USB for backup storage
typically leave the external HDD connected indefinitely, which eventually
causes problems. At some point the USB host controller will reset the port.
There are also issues with power management where host controllers will put a
port to "sleep" and issues with the amount of power delivered to the port not
being consistent.
PCIe on the other hand, is a much more robust interface. Once you plug it in
and power it on, it stays that way until the rapture. Less variance in how
vendors implement it.
In Linux, the USB host controller drivers include a system of "quirks" which
are enabled/disabled based on the make/model of the chip. For example, here's a
bit of code from the latest stable kernel where they describe enabling one of
these quirks for Intel hosts.
<code>
/* Existing Intel xHCI controllers require a delay of 1 mS,
* after setting the CMD_RESET bit, and before accessing any
* HC registers. This allows the HC to complete the
* reset operation and be ready for HC register access.
* Without this delay, the subsequent HC register access,
* may result in a system hang very rarely.
*/
if (xhci->quirks & XHCI_INTEL_HOST)
udelay(1000);
</code>
Note how this specifically calls out Intel. As if other vendors don't implement
this same 1ms delay?
-Ben
