Dma Commands; Dma Queued Commands - IBM IC35L020 - Deskstar 20 GB Hard Drive Specifications

14.4 DMA commands

DMA commands are:
O
Read DMA
O
Write DMA
Data transfers using DMA commands differ in two ways from PIO transfers:
O
data transfers are performed using the slave DMA channel
O
no intermediate sector interrupts are issued on multisector 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 for the following reasons:
O
no intermediate sector interrupts are issued on multisector commands
O
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.
1. Host initializes the slave DMA channel
2. Host writes any required parameters to the Features, Sector Count, Sector Number, Cylinder and
Device/Head registers.
3. Host writes command code to the Command Register
4. The device sets DMARQ when it is ready to transfer any part of the data.
5. Host transfers the data using the DMA transfer protocol currently in effect.
6. When all of the data has been transferred, the device generates an interrupt to the host.
7. Host resets the slave DMA channel.
Host reads the Status Register and, optionally, the Error Register.

14.5 DMA queued commands

These commands are:
O
Read DMA Queued
O
Service
O
Write DMA Queued
1. Command Issue
a. The host writes any required parameters to the Features, Sector Count, Sector Number, Cylinder,
and Device/Head registers.
b. The host writes command code to the Command Register.
c. The device sets BSY.
d. The device clears or sets REL.
Deskstar 60 GXP Hard disk drive specification
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