TODO revision 1.12 
1Some things that need to be done in no particular order:
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4Add lots of bus_dmamap_sync().
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6Implement isochronous transfer mode.
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8Implement audio driver.
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10Do bandwidth accounting.
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12Use lock manager locks.
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14Use the pool allocator for TDs et al.
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16Throw out more USBDI gunk.
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18Make hub driver note transition between self and bus powered state.
19Handle overcurrent conditions.
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21Make it possible to preallocate DMA buffers to avoid calling the
22memory allocator from an interrupt context.
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24Move memory allocation and copying to HC independent code.
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26Use a TD chain in ohci.c to allow transfers > 8K.
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28Document device driver API.
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30Document HC driver API.
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