Dma Commands - Hitachi 7K400 - Deskstar Hard Drive Specifications

11.4 DMA commands

The following are DMA commands:
• Read DMA
• Read DMA Ext
• Read Stream DMA
• Write DMA
• Write DMA
• Write Stream DMA
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 multisector commands.
Initiation of the DMA transfer commands is identical to the Read Sector(s) or Write Sector(s) commands with one
exception: the host initializes the Slave DMA channel prior to issuing the command.
The interrupt handler for DMA transfers differs in two ways:
• No intermediate sector interrupts are issued on multisector commands.
• The host resets the DMA channel prior to reading status from the device
The DMA protocol allows high performance multitasking operating systems to eliminate processor overhead asso-
ciated with PIO transfers.
• Host write any required parameters to the Features, Sector Count, Sector Number, Cylinder and
Device/Head registers.
• The host initializes the Slave DMA channel.
• The host writes any required parameters to the Features, Sector Count, Sector Number, Cylinder, and
Device/Head registers.
• The host writes command code to the Command Register.
• The device sets DMARQ when it is ready to transfer any part of the data.
• The host transfers the data using the DMA transfer protocol currently in effect.
• When all of the data has been transferred, the device generates an interrupt to the host.
• The host resets the Slave DMA channel.
• The host reads the Status Register and, optionally, the Error Register.
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