Re: [usb] Zero length data packet?

["Vikas T Rao " <vikasraot@myw.ltindia.com>]

** Proprietary **

NAK will be sent by device

1. only if some data is available on the device side but unable to send it at present moment.
2. when the device is unable to process the IN token immediately after it was received, though no further data needs to be sent by the device(since it doesn't have any data left out). probably in this case, device(h/w) will send a NAK to the IN token presently. during the next IN, the device(firmware) might have processed the previous IN such that it sets a bit(s). h/w will now see this bit(s) and sends a zero-length data packet now.

the 2nd reason might seem confusing but it happens where-in lot of other tasks have to be executed by the device apart from USB communication.

....vikas.

>>> vsn@yahoo.com 12/27/02 12:32PM >>>
Hi
Will not the device send NAK packet when it doesnt have data to send?
vsn

----- Original Message ----- 
From: "Vikas T Rao " <vikasraot@m... > 
To: <usb@o... > 
Date: Tue, 24 Dec 2002 14:39:23 +0530 
Subject: Re: [usb] Zero length data packet? 

> 
> 
> ** Proprietary ** 
> 
> hi, 
> 
> the device's endpoint can send zero-length packets for 
> bulk/interrupt In transcations during any of the following 
> conditions. 
> 
> 1. if the last packet is equal to max. packet size and there is no 
> further data to be sent. 
> 2. if the host sends an IN (due to some reasons) even though the 
> device has sent the last packet less than the max. packet size. 
> 3. if there is no data available on the device side at all. 
> 
> in the last 2 reasons, why host is sending IN and why device has no 
> data at all, depends on the implementations aspects of host or 
> device. 
> 
> ...vikas. 
> 
> >>> skashyap@t...  12/24/02 11:20AM >>> 
> 
--
To unsubscribe from usb mailing list please visit http://www.opencores.org/mailinglists.shtml

--
To unsubscribe from usb mailing list please visit http://www.opencores.org/mailinglists.shtml