>> > /*lowaddr*/BUS_SPACE_MAXADDR_32BIT,
>> > /*highaddr*/BUS_SPACE_MAXADDR,
>>
>> low and high address of the region that the DMA engine cannot access.
>
>Meaning e.g. the 16Mbyte barrier that ISA DMA has?
>For PCI this would be a 4Gb range(?).
The range could be much larger than 4GB. Remember this is a range the
device *cannot* access, not a range it can access. So, the beginning
of the range for an ISA device would be BUS_SPACE_MAXADDR_24BIT and the
hight address would be BUS_SPACE_MAXADDR. Depending on the platform
or configuration of the machine, the high address could be larger than
a 32bit quantity.
>> > /*maxsize*/MAXBSIZE,
>>
>> Maximum DMA transfer size.
>>
>> > /*nsegments*/AHC_NSEG,
>>
>> Maximum number of discontinuities in the mapped region.
>
>Eh.. ?
>
>> > /*maxsegsz*/AHC_MAXTRANSFER_SIZE,
>>
>> Maximum size of a segment. maxsize <= nsegments * maxsegsz.
>
>Eh.. ?
Many DMA engines have S/G capability and so can perform a single DMA that
spans multiple segments of "bus space contiguous" data. By setting these
parameters, the bus_dmamap_load function can determine how best to map
your transfer into bus space and will return to you an array of segments
to program into your DMA hardware.
>> You should use the new API if possible.
>
>That is what I'm planning to do. The amount of sample code in the various
>drivers is rather limited as most drivers use the old code.
It seems that its mostly confined to the SCSI code, but hopefully that will
change over time.
>So I hope you don't mind me asking some more questions,
Not a problem.
--
Justin
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