Dma Queued Commands - IBM DTTA-351010 - Deskstar 10.1 GB Hard Drive Specifications

data transfers are performed using the slave-DMA channel
no intermediate sector interrupts are issued on multi-sector commands
Initiation of the D M A 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 D M A transfers is different in that:
no intermediate sector interrupts are issued on multi-sector commands
the host resets the D M A channel prior to reading status from the device.
The D M A protocol allows high performance multi-tasking operating systems to eliminate processor over-
head 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 D M A R Q when it is ready to transfer any part of the data.
5. Host transfers the data using the D M A 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
8. Host reads the Status Register and, optionally, the Error Register

11.5 DMA Queued Commands

These commands are:
Read D M A Queued
Service
Write D M A 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.
e. The device clears BSY.
2. Data Transfer and Command Completion
If the device is ready for data transfer (REL is cleared),
a. The host transfers the data for the command identified by the Tag number using the D M A transfer
protocol currently in effect.
b. When all of the data has been transferred, the device generates an interrupt to the host.
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Command Protocol