On Tue, 9 Oct 2012 10:12:13 +0100
John <[email protected]> wrote:
> I was under the impression that anyone wanting (*) a USB COM port would
> buy the cheapest device going. Which I thought would not have an FTDI.
>
Not necessarily. If your uC has a USB port (most do these days),
then you can implement your own USB stack and use that as a COM
port.. or something more suited to your application.
And yes, we did exactly that.
> I tend to agree but USB seems to suffer a communication problem, by
> which I mean communication to people, i.e. failing to explain simply and
> usefully how it works, how to use it and why. There seem to be big
> barriers to entry i.e. it is hard to get a quick overview and get on
> using it as a packet transport (or any other usage). People give up and
> go back to virtual COM port, which is easy to grasp and already well
> known plus has lots of existing software that "works" (very suboptimally
> in this case).
Actually, USB is not that hard, and more importantly it's open and
well documented free of charge. Just go to usb.org and download the
USB standards zip. You get everything you need. Try the same with
SD Card or PCI or ethernet or ...
Yes, the standard can be overwhelming (same as every other non-trivial
standard i know), but there are good books around that help you getting
started, [1] might be a good example.
Oh, and a little hint: if you start developing your own USB stack,
use linux as a test host. Windows will crash at every opportunity
if even one byte in a descriptor is wrong. And watch out for bugs
in USB hardware implementations and their documentation. You'd be
surprised how many companies get even the most basic things wrong
(like Atmel's SAM7 allowing to send 65 byte packets in FullSpeed,
when the standard sets an upper limit of 64... and no way to recover
from that condition but a reset).
And don't forget to use the standard conformance test applications[2]
on your device.
Attila Kinali
[1] USB Complete, by Jan Axelson
[2] http://www.usb.org/developers/tools/
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