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DISK DRIVE OPERATION
SpinPoint V40 Product Manual
87
6.6.4 DMA Data Transfer Commands
This class comprises:
•
Read DMA (C8h)
•
Write DMA (C9h)
Data transfers using DMA commands differ in two ways from PIO transfers:
•
Data transfers are performed using the slave-DMA channel,
•
No intermediate sector interrupts are issued on multi-sector commands.
Initiation of the DMA transfer commands is identical to the Read Sector or Write Sector commands except
that the host initializes the slave-DMA channel prior to issuing the command.
The interrupt handler for DMA transfers is different in that:
•
No intermediate sector interrupts are issued on multi-sector commands,
•
The host resets the DMA channel prior to reading status from the drive.
The DMA protocol allows a high performance, multi-tasking operating system to eliminate processor
overhead associated with PIO transfers.
a) Command phase
1) Host initializes the slave-DMA channel.
2) Host updates the Command Block registers.
3) Host writes command code to the Command register.
2) Host updates the Command Block registers.
3) Host writes command code to the Command register.
b) Data phase. The register contents are not valid during a DMA data Phase.
1) The slave-DMA channel qualifies data transfers to and from the drive with DMARQ.
c) Status phase
1) Drive generates the interrupt to the host.
2) Host resets the slave-DMA channel.
3) Host reads the Status register and Error register.
2) Host resets the slave-DMA channel.
3) Host reads the Status register and Error register.