On Mon, 18 Aug 2003, Matthias Bruestle wrote:

> Somewhere inside a program run, when waiting for the interrupt data:
> 
> HC status
>   usbcmd    =     00c1   Maxp64 CF RS
>   usbstat   =     0000
>   usbint    =     000f
>   usbfrnum  =   (0)194
>   flbaseadd = 03848194
>   sof       =       40
>   stat1     =     0095   PortEnabled PortConnected
>   stat2     =     0095   PortEnabled PortConnected
> Frame List
> Skeleton QH's
> - skel_int4_qh
>     [c3858240] link (03858122) element (03859030)
>       0: [c3859030] link (00000001) e3 SPD IOC Active NAK Length=7ff MaxLen=f DT0 
> EndPt=1 Dev=5, PID=69(IN) (buf=05a5f520)
> 
> In the second program run, the Active for Int IN is always set when an
> interrupt occures.

The NAK flag above means that the HC issued the Intr IN request and the 
device replied with a NAK.  That would explain the packets you see going 
across the wire.  But why would the device NAK?  For some reason, it must 
not have any interrupt data available.  Or maybe there's a problem with 
the maxpacket size? -- the request is asking to transfer a 16-byte packet.

My guess would be that in your unsuccessful run, something isn't getting 
initialized correctly and as a result the device doesn't queue any 
interrupt data.

Alan Stern



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