On Dec 12, 2016, at 6:11 PM, Scott Deandrea <sdeand...@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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