IOMemoryCursor segment size issue

13 Jun 2002

      Hi,

I am creating an IOMemoryCursor using:

    CursP = IOMemoryCursor::withSpecification ( SegFn, UINT_MAX, UINT_MAX,

1 );

which gives me a valid MemoryCursor.

I then call CursP->genPhysicalSegments(    MemDescP,

                                           start,

                                           Segments,

                                           NumSegments,

                                           MaxTransferSize,

                                           &BytesToTransfer );

    to create the DMA address/len pairs I require in 'Segments'.

When I debug SegFn, the Segment.length field is ALWAYS 4096 regardless of

the values passed to the withSpecification function above. This gives me a

max transfer size of 0.5Mb (128 entries), which is way too small for my

requirements.

Questions:

1. Why does my segment function ONLY get 4k segments? What am I doing wrong?

2. When 'wiring' the User buffer, do I just need to 'prepare' the

MemoryDescriptor,

   or do I need to 'map' it as well?

Thanks in advance,

Peter Young

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