Re: DLT_ request

[Guy Harris <guy () alum mit edu>]

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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