15 Jun
2013
15 Jun
'13
1:04 p.m.
On Sat, 15 Jun 2013, Josh Dersch wrote:
For suitable values of 'everything;. OK, most machines can easily become
USB slaves (e.g. by the FTDI USB to async serial chips) but only one
machine I own can be a USB host (the Rpi). That is NOT universal.
And the 'ability to chain it' is hardly unique to USB. HPIB (GPIB
IEEE-488), HPIL, HP-HIL, etc coulds all support multiple periperhals on
one interface.
Let's see...
I *think* that based on prior history (and correct me if I'm wrong) that
the next subject should be about how USB is not, infact, a "bus" and is
stupid and awful and can't be interfaced to a ZX Spectrum and therefore
is a failure oh God make it stop make it stop make it stop.
It's a commercial success, and it is extremely versatile...it DOES work on
everything. The ability to chain it is nice, too.
However...it's too low-current and low-speed for some stuff (at least
in USB 2.0). There's also no DMA...is there? (I could be wrong)
There is no reason =why a USB interface device can't do DMA into the host
computer's memory. What is really missing (IMHO) are interrupts (service
requests, whatever) on the USB link iteslf.
However...the connectors are a failure. There are too many nonstandard
ones, and too many to choose from that are JUST EVER SO SLIGHTLY
MECHANICALLY DIFFERENT but are electrically identical. It's ridiculous.
And to think that one moan about RS232 was that there were different
connectors used.
-tony