We may be transferring less data than can fit in a chunk, so we need
to ensure that xfer_cnt is clamped to 0 when transferring the last
chunk (otherwise it remains negative, and has_data() will return true).
It's also possible that the transfer size is bigger than a chunk but not
an even multiple of the chunk size, so we need to ensure that we don't
try to transfer a whole chunk in the last iteration.
More correctly initialize the device identification struct, to report
the maximum (word 47) and current (word 59) number of blocks that can be
transferred with READ_MULTIPLE and WRITE_MULTIPLE commands.
Fix post_xfer_action to write the actual data size that was written,
as opposed to an entire chunk (which may be larger).
1f2256ec81a/7ee8b9b2 were referencing a multiple_sector_count field,
but it was never set. This was resulting in an error being returned
(`READ MULTIPLE with SET MULTIPLE==0`).` We actually should use
`sec_per_block``, which bd16b7c69e introduced.
Although being optional in ATA-3 and absent in >= ATA-4,
RECALIBRATE is issued by Open Firmware 3.1.1 during device
initialization. If it fails, the drive is considered non-bootable.
The total size needs to have 3 factors cylinders, heads, & sectors. Imagine a disk having a total size with 3 prime factors 3 x 5 x 11. 15 cannot be assigned to heads because that would only leave 11 for sectors and cylinders. Therefore, test all heads and sectors combinations. If the third factor for cylinders is not found, then choose 16 heads, then the minimum number of sectors, and finally the maximum number of cylinders. The loop could be changed to skip values of heads that are not a factor, but it doesn't take any time to try them all.
Allows different implementations for different platforms (the JS
build relies on browser APIs to stream disk images over the network).
Setting aside the JS build, this also reduces some code duplication.
