TODO revision 1.5 
1Some things that need to be done in no particular order:
2
3Implement request timeout and abort in ohci.c.
4
5Implement isochronous transfer mode.
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7Implement audio driver.
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9Do bandwidth accounting.
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11Use lock manager locks.
12
13Implement a modem driver for the Abstract Control Model.
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15Use the pool allocator for TDs et al.
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17Merge soft_td and td in uhci.c.
18