[sdiy] Daft Idea, LINUX SYNTH

[Byron G. Jacquot]

>Haven't seen single USB *host* controllers on mobos, AFAIK they usually
>are integrated into one of the bridges. The chips you get here and there
>are pure slaves which is fine for any attached module but not for the
>beast who needs to drive the USB bus.

There are some standalone USB host controller chips out there.  I can't
recall the maker, but there was an "11" in the model number of the one I
almost used.

>Finally, at least UHCI controllers need quite some software overhead (see
>the Linux UHCI drivers) that you certainly don't want to implement this
>mess into a DIY synth. In that case, one could just use an ordinary PC as
>the main controller and put some OS of choice on it - probably not the way
>most people would like it.

The HUGE software overhead of a USB host actually led me away from using USB
in a commercial product recently.  We only wanted to be able to add
something akin to a floppy drive, so it initially seemed like an OK
technology.  The fact that the subordinate devices can be really simple is
deceptive...a USB host controller requires quite a bit of software, and
needs many layers of protocol, even if you only want to support a single
class of device.  There's also a realtime impact, as the host has to do bus
administration every millisecond.  We wound up using NAND flash cards
instead of disks, with relatively trivial software to control it.

If the host were a PC or Mac, then USB might be OK, but building a USB host
around a microcontroller would not be trivial.

Anyone for a 3-wire bus?