Re: [usb] Info Reqd

[Rudolf Usselmann <rudi@asics.ws>]

On Thu, 2002-12-26 at 13:34, Vikas T Rao wrote:
> ** Proprietary **
> 
> hi,
> 
> ACK has to be sent when any of the following condition occurs.

I think you meant "... when *all* of the ..."

> 1. when there is no CRC error
> 2. when there is no bit stuff error
> 3. when the received message(token and data packets) is appropriate for the endpoint under consideration
> 
> sending ACK depends on one's own implementation aspects. ideally firmware(f/w) has to interact with h/w. one option in such case could be, f/w should set a bit(or a group of bits) in the register such that h/w will send ACK if this bit is set(active). then h/w will make this bit inactive immediately after sending.

I think you don't have enough time to make this decision by
software. My impression was it had to be done in hardware.
Check the usb spec to see how long of a latency is allowed
and then decide if you can do it in software or not.

I think Vikas suggestion is excellent.

rudi

> ....vikas
> 
> >>> sinax_usb@yahoo.com 12/26/02 10:50AM >>>
> 
> Hi,
> I am currently working on developing a USB device stack.My question is:
>    What is the condition for ACK to be sent frm the device: Is it just CRC pass in which case the hardware sends the ACK or is it the endpoint successfully receiving the message?To send an ACK does the s/w interact with the h/w?
> 
>
-- 
rudi
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