ATAPISCSI(4) BSD Kernel Interfaces Manual ATAPISCSI(4)
atapiscsi -- ATAPI<->SCSI adapter
atapiscsi* at wdc? flags 0x0000
atapiscsi* at pciide? flags 0x0000
The atapiscsi driver supports ATAPI (also called IDE) devices such as CD-
ROMs, ZIP drives, LS-120 floppy drives, and tape drives. All ATAPI
devices talk a subset of the SCSI protocol.
The atapiscsi driver acts like a SCSI adapter. Thus, the ATAPI devices
connected to the system will appear as SCSI devices. ATAPI CD-ROMs will
appear as cd(4) devices, ATAPI tape drives as st(4) devices, and ATAPI
floppies as sd(4) devices.
For performance reasons, one should avoid putting an ATAPI device and a
hard disk on the same cable. The driver does not support bus release
and, even if it did, many ATAPI devices do not support it. There is only
one command outstanding on a cable at a time. For example, if a hard
disk and a CD drive are placed on the same cable, the hard disk requests
may get queued behind slower CD operations.
The flags are used only with controllers that support DMA operations and
mode settings (like some pciide(4) controllers). The lowest order
(rightmost) nibble of the flags define the PIO mode to use. The next
four bits indicate the DMA mode and the third nibble the UltraDMA mode.
For each set of four bits, the 3 lower bits define the mode to use and
the last bit must be set to 1 for this setting to be used. For DMA and
UltraDMA, 0xf (1111) means ``disable''. For example, a flags value of
0x0fac (1111 1010 1100) means ``use PIO mode 4, DMA mode 2, disable
UltraDMA''. The special setting 0x0000 means ``use whatever the drive
claims to support''.
cd(4), intro(4), pciide(4), scsi(4), sd(4), st(4), wdc(4)
Slow devices, like tape drives, could do a better job of sharing the
channel. For now, we recommend you put the tape device on its own chan-
BSD August 14, 2012 BSD