Samsung 3.5" hard disk drives, spinpoint v40 manual DMA Data Transfer Commands

DISK DRIVE OPERATION

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.

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.

SpinPoint V40 Product Manual 87