From: Marko Mäkelä (msmakela_at_gmail.com)
Date: 2008-03-05 15:21:23
On Thu, Mar 06, 2008 at 12:45:53AM +1100, Mark McDougall wrote:
> Your mouse, OTOH, sends regular updates to the host via the USB slave
> chip, which buffers data and send to the host at most every (IIRC) 10ms -
> the USB HID interrupt packet rate. It can choose to send less regularly,
> especially if you're not moving the mouse.
I may be wrong, but doesn't the USB "interrupt" transfer mode mean that
the host must be polling the devices every x milliseconds?
In any case, I believe that the only way to implement a USB host is to
use an interface chip for that. Or a chip that embeds the USB
controller on the processor core. Depending on how the chip is
impelmented and what the USB specification says about the interrupt mode,
even then the implementation on a C64 could violate the specification,
for example, when accessing other peripherals.
On a somewhat related note, there is a USB charging specification that
says that a special charger (5 V, 500..1500 mA) must identify by
shorting the data lines. This means that it is impossible to implement
a USB device (such as a sensor in the USB HID class) that at the same
time acts as a compliant charger for USB on-the-go hosts. It would be
much easier to implement a USB device than a USB host.
Marko
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