[rescue] USB port card for sBus?

der Mouse mouse at Rodents-Montreal.ORG
Sun Aug 24 00:45:19 CDT 2008

> If you can find an off-the-shelf USB-to-EIA232 adapter

...I'll be slightly surprised.  (Lots of them are electrically
moderately close, at least for the signals they bother to implement,
but ignore the mechanical portion of the spec, typically using a DE9
instead of a DB25.)

> that will magically sense which role it's supposed to play [...], and
> will make that determination and a complete USB device tree by merely
> swapping the gender of the USB side and receiving power from
> elsewhere, [...].

> The bus Does Not work that way.

It could.  It would be quite easy to make that determination based
purely on where power is coming from, I daresay.

> But, yes, if you wanted to create a USB controller, presumably
> mastering the bus at a nominal 11Mb/s or 480Mb/s, that talked back to
> the host system over a SPARCstation's Z8530-powered serial ports at a
> blazing 230Kb/s,

The fastest they can reliably go is 76800 (at least in the ones I know,
which basically means pre-Ultra - do any sparc64s use 8530s?).  If you
use the chip's w1 mode, you can go as fast as 1228800, but then you're
just _asking_ for input corruption due to bit edge misalignment.

Where'd you get 230Kbps?

> that would probably be an excellent investment of some engineer's
> time--much better than an SBus or PCMCIA implementation.

Sarcasm aside, it certainly would be in some respects.  For starters,
it would not be tied to SBus- or PCMCIA-capable hardware.

The speed mismatch would be painful for many applications, but I
certainly know that often enough I have a device that speaks interface
A and want to connect it to a machine with interface B and don't really
care much about performance - working like a pig moves bits faster than
not working at all.

And, for all that they're disappearing, I think serial ports are still
the closest thing around to a universally-available interface -
certainly so in view of what list this is.

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