Implement ATA DMA and fix DBDMA resCount calculation#191
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Edit: should work now - there was a "magic" timeout needed for assert_dmareq - added a TODO since the more correct fix is invasive. |
Handle ATA DMA reads and writes for hard disks. Reads prepare data from the backing image and writes accept pushed data from the DBDMA channel until the programmed sector count is exhausted. The `data_ptr` in `AtaBaseDevice` needs to be advanced after each DMA pull so one request can be split across multiple DBDMA descriptors.
We were treating resCount as a "result" count, but it's actually a "residual" count that reports how many bytes from a descriptor were not transferred when processing a command. We now correctly handle partial descriptors. This ended up being necessary for the 10.0 public beta bringup too (the `AppleUltra66ATA::stopDma` implementation in xnu-103 computes the number of bytes transferred by subtracting `resCount` from `reqCount`).
Mac OS X Public Beta commonly drives one ATA DMA transfer through multiple DBDMA descriptors, so a single ATA pull can be smaller or larger than the current descriptor request without indicating an error. Reduce the logging level to avoid logspam during boot.
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Three commits, see the individual commit messages for details (should not be squashed when merging):
resCountto return the "residual" value, which matches the CHRP spec and xnu implementationFixes #154