Hitachi 7K400 Specifications - Page 121
DMA commands
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UPC - 000053412935
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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 associated 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. Deskstar 7K400 Hard Disk Drive Specification 107
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