[usb] Doubt on Keep Alive

["R Rajaganapathy" <rajachola@tataelxsi.co.in>]

Hi everybody,

     From section 11.8.4.1 of USB Spec

The hub can generate the keep-alive on any valid full-speed token packet. The following rules

for generation of a low-speed keep-alive must be adhered to:

A) A keep-alive must minimally be derived from each SOF. It is recommended that a keep-alive be generated on any valid full-speed token.

B)  The keep-alive must start by the eighth bit after the PID of the full-speed token.

questions:

 

As per  point B " The keep-alive must start by the eighth bit after the PID of the full-speed token"

1. why this timing is needed only for "keep alive" ?

2. What happens if above timing is not met i.e Keep alive sent imediately after decoding  full speed token ?

 

 

Thanks in advance

 

regards

Rajaganapathy