----- Original Message -----
From:
Thierry LEROUX
Sent: Tuesday, February 26, 2002 3:27
PM
Subject: RE: [usb] Regarding Frames and
Microframes
Hi,
These frames are "token only" transactions. They do not need any ACK or
NAK to be handled.
There is a 8 bits PID + 11 bits of frame # + 5 bits CRC (= 3
Bytes).
The
Frame # is a 11 bits system wide time frame. Use of it is function dependent.
You can imagine to use it to maintain a common system wide time frame (For
example to synchronise audio equipments ...).
The
"tick" time is 1 ms.
In
addition, there is µ-frame ticks (125 µs) if the function is 2.0 compatible.
In that case you need some local computation to create a 15 bits
counter.
We
found this SOF very useful for synchronization over the whole bus and between
connected devices.
I
hope this help.
Thierry
Hi all,
I am Veeresh newly
joined this mailing list. While going through the USB Spec. 2.0, I got some
doubts in Start Of Frame (SOF). As these frames are token only transactions,
what is the significance of these frames? What the 11-bit frame
indicates?
Thanks and
regards,
Veeresh
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