Re: DLT_ request

[Scott Deandrea <sdeandrea () apple com>]

Yes, if there are fewer tiers of hubs, the unused nibbles will be zero.

Correct, the padding is only added if frameLength isn’t a multiple of 4.  This should be considered the final version.  
The timestamps are in Mach Absolute Time Units (https://developer.apple.com/library/content/qa/qa1398/_index.html 
<https://developer.apple.com/library/content/qa/qa1398/_index.html>).

—scott

> On Dec 12, 2016, at 9:49 PM, Guy Harris <guy () alum mit edu> wrote:
>
> On Dec 12, 2016, at 6:11 PM, Scott Deandrea <sdeandrea () apple com> wrote:
>
> > The bus number is 0 based and the port numbers are 1 based.
>
> So if there are fewer than 6 ports in the route, the unused nibbles will be zero.
>
> > I decided to implement isochronous transfers today and changed the structure slightly:
> > struct
> > {
> >   // Control information
> >   uint32_t frameHeaderLength;  // 28
> >
> >   // Frame information
> >   uint32_t frameLength;   // Amount of data sent/received this frame
> >   uint32_t frameStatus;    // IOReturn result of the I/O this frame 
> >   uint64_t frameNumber; // Frame number on which this was scheduled/executed by the controller
> >   uint64_t ioTimestamp;  // Time in which the frame completed
> > } __attribute__((packed, aligned (sizeof(uint32_t))));   
> >
> > Therefore, the isochronous format for a request with type kAppleUSBHostPacketFilterRequestComplete is as follows:
> > Link Header
> > padding, if required to force 4-byte alignment
> > Isochronous Frame[0] Header (frameHeaderLength bytes in length)
> > Isochronous Frame[0] Data (frameLength bytes)
> > …
> > padding, if required to force 4-byte alignment
> > Isochronous Frame[linkHeader.ioFrameCount - 1] Header (aligned to 4 bytes, frameHeaderLength bytes in length)
> > Isochronous Frame[linkHeader.ioFrameCount - 1] Data (frameLength bytes)
>
> So the headers and data are interleaved; the padding would presumably be needed only if frameLength isn't a multiple 
> of 4.
>
> Is this the final version, or should the format of a payload of a packet for an isochronous endpoint be left 
> unspecified for now until it's finalized?
>
> Also, what are the formats of the time stamps?  What are the units, and is there a specified origin or are they just 
> relative to an unspecified base time?

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