TODO revision 1.7 
1Some things that need to be done in no particular order:
2--------------------------------------------------------
3
4Implement isochronous transfer mode.
5
6Implement audio driver.
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8Do bandwidth accounting.
9
10Use lock manager locks.
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12Use the pool allocator for TDs et al.
13
14Merge soft_td and td in uhci.c.
15      soft_qh and qh
16      soft_ed and ed in ohci.c
17      soft_td and td
18
19Tidy up transfer completion.
20
21Throw out more USBDI gunk.
22
23Port FreeBSD umass driver.
24
25Make hub driver note transition between self and bus powered state.
26Handle overcurrent conditions.
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