[Info-vax] USB based serial ports, was: Re: Useless Serial Bus

[Simon Clubley]

On 2011-10-31, Jose Baars <peutbaars at googlemail.com> wrote:
> On Oct 31, 11:49 pm, Simon Clubley <clubley at remove_me.eisner.decus.org-
> Earth.UFP> wrote:
>> On 2011-10-29, JF Mezei <jfmezei.spam... at vaxination.ca> wrote:
>>
>> That should be "brain dead under Windows". All the reports I've seen say
>> that the Linux USB CDC driver works just fine.
>>
> You might be right, but from where I am looking at least the FTDI
> drivers have been
> incorporated in the Linux kernel.  Also the driver is GPL'ed and
> downloadable from
> the FTDI website. Some or part of these drivers have been reverse
> engineered from the
> Windows dll provided bij FTDI, though.
> Why the drivers would work better under Linux than under Windows, or
> OS/X, seems
> unlikely to be caused by the drivers.

I think there may be some misunderstanding about what I (and JF) were saying.

The USB specification includes a Communications Device Class (or CDC)
specification for connecting serial type devices.

This is a fully open standard and in any sane world, there would be little
need for a vendor to supply their own serial drivers as any extensions
could be handled, for example, as a HID type device (just as the MCP2200
does) or implemented in another way (for example, CTS based flow control
appears to be handled internally by the MCP2200 when activated).

However, the CDC driver supplied by Microsoft as part of it's Windows USB
stack is reported to be so bad that vendors have had to implement their own
vendor specific API (which they promptly went and closed) and hence use it
on all operating systems; even the ones for which the functionality could be
implemented using open USB standards.

BTW, knowledge gained from looking at the driver source is quite fragile as
it only tells you how something works under one specific set of circumstances.
It does not tell you _why_ something is done in that way and what additional
steps may be required of something changes. For that, you need a full
specification.

Simon.

-- 
Simon Clubley, clubley at remove_me.eisner.decus.org-Earth.UFP
Microsoft: Bringing you 1980s technology to a 21st century world