Re: raw1394_start_iso_write ?

[Dan D. <dde...@co...>]

From: "Ken Offer"
> Hi Andreas (et. al),
>
> I'm looking for an explanation of the parameters for this routine:
>
> int raw1394_start_iso_write(struct raw1394_handle *handle,
>                             unsigned int channel,
>                             unsigned int tag,
>                             unsigned int sy,
>                             unsigned int speed,
>                             size_t length,
>                             quadlet_t *data,
>                             unsigned long rawtag);
>
> Please correct me if I'm wrong in these assertions:
>
> The "handle" parameter is returned from
> raw1394_get_handle().

Yes

> The "channel" parameter is the isochronous channel to use
> during transmission.  It ranges from 0 to 63?

Yes

> The tag parameter should be either:
>
> a. some register offset from CSR_REGISTER_BASE
>    (perhaps CSR_REGISTER_BASE+CSR_FCP_COMMAND?)

No

> b. some value which distinguishes the packet type from
>    other packet types?
>
> c. something else?

Specific to the protocol. It can indicate the inclusion of CIP headers in
the iso data packet.

> The "sy" parameter is a complete mystery to me.  Is it the
> "Z" parameter that the 1394 Open Host Controller Interface
> Specification references?

No, the Z field is part of the DMA command descriptor.
The Sy is specific to the protocol too. For example, DV does not use it; it
always 0. Uncompressed video via Digital Camera sets this to 1 to indicate
the start of a new frame.

> The "speed" parameter should be 1 for 100Mbits/sec, 2 for
> 200Mbits/sec and 3 for 400Mbits/sec (this I gleaned from the
> 1394 Open Host Controller Interface Specification referenced
> from the links page).

Yes

> The "length" parameter is the size of whatever data points to.

Yes

> The "data" parameter is:
>
> a. A pointer to a buffer of raw data to send

Yes

> b. A pointer to some "DMA data-structure/program" that is described
>    in the 1394 Open Host Controller Interface Specification.

No

> c. Something altogether different.
>
> d. An android serving on a starship in the 24th century. :)
>
> The "rawtag" parameter is another mystery.  Is it the same value as
> tag?

Hmm... I don't recall that parameter. It is a full quadlet, so perhaps it
allows one to completely format the iso header and access some reserved
areas?

> Any pointers you could offer would be greatly appreciated.
>
> --
> ______________________________________________________________
> Kenneth Ray Offer, II
> Sr. Systems Analyst
> Applied Research Laboratories/SDD
> University of Texas at Austin
> Office (512) 835-3859   FAX (512) 835-3259
>
> Any opinions expressed above are mine and not necessarily
> those of my employer.
>
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